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Date:   Tue, 12 May 2020 23:10:56 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
To:     Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Cc:     linux-renesas-soc@vger.kernel.org, linux-media@vger.kernel.org,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        Kieran Bingham <kieran.bingham@ideasonboard.com>,
        Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        Jacopo Mondi <jacopo@jmondi.org>,
        Niklas =?iso-8859-1?Q?S=F6derlund?= 
        <niklas.soderlund@ragnatech.se>, sakari.ailus@iki.fi,
        Hans Verkuil <hverkuil@xs4all.nl>,
        Hyun Kwon <hyunk@xilinx.com>, Rob Herring <robh+dt@kernel.org>,
        Jacopo Mondi <jacopo+renesas@jmondi.org>,
        Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>,
        Niklas =?iso-8859-1?Q?S=F6derlund?= 
        <niklas.soderlund+renesas@ragnatech.se>
Subject: Re: [PATCH v9 2/4] media: i2c: Add MAX9286 driver
Message-ID: <20200512174056.GH5526@Mani-XPS-13-9360>
References: <20200512155105.1068064-1-kieran.bingham+renesas@ideasonboard.com>
 <20200512155105.1068064-3-kieran.bingham+renesas@ideasonboard.com>
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In-Reply-To: <20200512155105.1068064-3-kieran.bingham+renesas@ideasonboard.com>
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Hi Kieran,

On Tue, May 12, 2020 at 04:51:03PM +0100, Kieran Bingham wrote:
> The MAX9286 is a 4-channel GMSL deserializer with coax or STP input and
> CSI-2 output. The device supports multicamera streaming applications,
> and features the ability to synchronise the attached cameras.
> 
> CSI-2 output can be configured with 1 to 4 lanes, and a control channel
> is supported over I2C, which implements an I2C mux to facilitate
> communications with connected cameras across the reverse control
> channel.
> 
> Signed-off-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
> Signed-off-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
> Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
> Signed-off-by: Niklas S?derlund <niklas.soderlund+renesas@ragnatech.se>
> 
> --
> v2:
>  - Fix MAINTAINERS entry
> 
> This posting is released with the following modifications to work
> without Sakari's VC developments:
>  - max9286_g_mbus_config() re-instated
>  - max9286_get_frame_desc() is not bus/csi aware
>  - max9286_{get,set}_routing() removed
> 
> v3:
>  - Initialise notifier with v4l2_async_notifier_init
>  - Update for new mbus csi2 format V4L2_MBUS_CSI2_DPHY
> 
> v4: - Re-introduce required code to function with the VC series.
> 
>  - Implement max9286_get_routing, max9286_set_routing
>  - Remove max9286_g_mbus_config
> 
> v5: (internal release)
>  - Fix printk formatting for hex value
>  - max9286->sd.flags |= V4L2_SUBDEV_FL_HAS_DEVNODE (add |)
>  - MEDIA_ENT_F_PROC_VIDEO_PIXEL_FORMATTER -> MEDIA_ENT_F_VID_IF_BRIDGE
>  - Remove 'device is bound' workaround
> 
> v6:
>  - v4l2_subdev_krouting instead of v4l2_subdev_routing separated
>    to allow integration without the VC/V4L2-Mux series.
>  - convert sd_to_max9286 to inline function
>  - rename max9286_device to max9286_priv
>  - Cleanup the v4l2_async_notifier
>  - Extend MODULE_AUTHOR
>  - Replace of_graph_get_endpoint_by_regs with fwnode_graph_get_endpoint_by_id
>  - Pass default bus type when parsing fwnode endpoint (Manivannan Sadhasivam)
>  - Use new YAML file reference in MAINTAINERS
>  - Parse new i2c-mux node in max9286_get_i2c_by_id
>    (This could/should be refactored to parse these separately first)
>  - Spelling and calculation fixes in the FSYNC_LOCKED check comments
>  - Identify each enabled i2c-mux channel in a single pass
>  - max9286: Improve mux-state readbility [v2]
>  - Fix frame sync lock durations
>  - Add comment to describe /why/ we must open the mux in s_stream
>  - use -EXDEV as return code for failed link synchronisation.
>  - Fix reference counting of the dt nodeS
>  - Convert to probe_new for I2C
>  - Remove redundant max9286_i2c_mux_state
>  - Provide optional enable-gpio (max9286-pwdn)
> 
> v7:
>  [Kieran]
>  - Ensure powerdown lines are optional
>  - Add a 4ms power-up delay
>  - Add max9286_check_config_link() to core
>  - Add GPIO chip controller for GPIO0OUT and GPIO1OUT
>  - Fix GPIO registration
>  - max9286: Split out async registration
>    (fixes regulator -EPROBE_DEFERs failures)
>  - Collect all V4L2 registrations
>  - balance v4l2_async refcnting
>  - Rename max9286_v4l2_async_ => max9286_v4l2_notifier_
> 
>  [Jacopo]
>  - Remove redundanct MAXIM_I2C_SPEED macros
>  - Move notifiers operations
>  - Add delay after reverse channel reconfiguration
>  - Move link setup to completion
>  - Fix up max9286_check_config_link() implementation
>  - Remove redundant dual configuration of reverse channel
> 
> v8:
> 
> [Kieran]
>  - Update the bound_sources mask on unbind
>  - Convert probe kzalloc usage to devm_ variant
>  - Fix up cleanup path from GPIO PowerDown registration
>  - cleanup GPIO device registration fail path
>  - Convert to use devm_regulator_get()
>  - Fit max9286_parse_dt print on one line
>  - Move multi-device workarounds out of upstream driver
>  - Remove I2C mod-table
>  - Lock format changes
>  - Describe pad index usage
>  - Remove poc_enabled workaround
>  - Rename the max9286_gpio to be more explicit on it's actions.
>  - Move max9286_init_format call
>  - Rework probe sequence and simplify error paths.
>  - Simplify i2c comments
>  - Implement Pixelrate control
>  - Disable overlap window
> 
> [Jacopo]
>  - Adapt Kconfig to latest upstream changes
>  - Put of node on error
>  - Calculate pixel rate
>  - Simplify overlap window disablement
> 
> v9:
> 
> [Kieran]
>  - Kconfig: Depend on OF
>  - Re-sort addition to Makefile
> ---
>  MAINTAINERS                 |   10 +
>  drivers/media/i2c/Kconfig   |   13 +
>  drivers/media/i2c/Makefile  |    1 +
>  drivers/media/i2c/max9286.c | 1332 +++++++++++++++++++++++++++++++++++
>  4 files changed, 1356 insertions(+)
>  create mode 100644 drivers/media/i2c/max9286.c
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index a7bb6e22d5da..99e3bf7760fd 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -10274,6 +10274,16 @@ F:	Documentation/hwmon/max6697.rst
>  F:	drivers/hwmon/max6697.c
>  F:	include/linux/platform_data/max6697.h
>  
> +MAX9286 QUAD GMSL DESERIALIZER DRIVER
> +M:	Jacopo Mondi <jacopo+renesas@jmondi.org>
> +M:	Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
> +M:	Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
> +M:	Niklas S?derlund <niklas.soderlund+renesas@ragnatech.se>
> +L:	linux-media@vger.kernel.org
> +S:	Maintained
> +F:	Documentation/devicetree/bindings/media/i2c/maxim,max9286.yaml
> +F:	drivers/media/i2c/max9286.c
> +
>  MAX9860 MONO AUDIO VOICE CODEC DRIVER
>  M:	Peter Rosin <peda@axentia.se>
>  L:	alsa-devel@alsa-project.org (moderated for non-subscribers)
> diff --git a/drivers/media/i2c/Kconfig b/drivers/media/i2c/Kconfig
> index 3abc80373ec0..2e390f41f6da 100644
> --- a/drivers/media/i2c/Kconfig
> +++ b/drivers/media/i2c/Kconfig
> @@ -464,6 +464,19 @@ config VIDEO_VPX3220
>  	  To compile this driver as a module, choose M here: the
>  	  module will be called vpx3220.
>  
> +config VIDEO_MAX9286
> +	tristate "Maxim MAX9286 GMSL deserializer support"
> +	depends on I2C && I2C_MUX
> +	depends on OF
> +	select V4L2_FWNODE
> +	select VIDEO_V4L2_SUBDEV_API
> +	select MEDIA_CONTROLLER
> +	help
> +	  This driver supports the Maxim MAX9286 GMSL deserializer.
> +
> +	  To compile this driver as a module, choose M here: the
> +	  module will be called max9286.
> +
>  comment "Video and audio decoders"
>  
>  config VIDEO_SAA717X
> diff --git a/drivers/media/i2c/Makefile b/drivers/media/i2c/Makefile
> index 77bf7d0b691f..f0b001ee4b05 100644
> --- a/drivers/media/i2c/Makefile
> +++ b/drivers/media/i2c/Makefile
> @@ -117,6 +117,7 @@ obj-$(CONFIG_VIDEO_IMX274)	+= imx274.o
>  obj-$(CONFIG_VIDEO_IMX290)	+= imx290.o
>  obj-$(CONFIG_VIDEO_IMX319)	+= imx319.o
>  obj-$(CONFIG_VIDEO_IMX355)	+= imx355.o
> +obj-$(CONFIG_VIDEO_MAX9286)	+= max9286.o
>  obj-$(CONFIG_VIDEO_ST_MIPID02) += st-mipid02.o
>  
>  obj-$(CONFIG_SDR_MAX2175) += max2175.o
> diff --git a/drivers/media/i2c/max9286.c b/drivers/media/i2c/max9286.c
> new file mode 100644
> index 000000000000..481d65f2b51d
> --- /dev/null
> +++ b/drivers/media/i2c/max9286.c
> @@ -0,0 +1,1332 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +/*
> + * Maxim MAX9286 GMSL Deserializer Driver
> + *
> + * Copyright (C) 2017-2019 Jacopo Mondi
> + * Copyright (C) 2017-2019 Kieran Bingham
> + * Copyright (C) 2017-2019 Laurent Pinchart
> + * Copyright (C) 2017-2019 Niklas S?derlund
> + * Copyright (C) 2016 Renesas Electronics Corporation
> + * Copyright (C) 2015 Cogent Embedded, Inc.
> + */
> +
> +#include <linux/delay.h>
> +#include <linux/device.h>
> +#include <linux/fwnode.h>
> +#include <linux/gpio/consumer.h>
> +#include <linux/gpio/driver.h>
> +#include <linux/i2c.h>
> +#include <linux/i2c-mux.h>
> +#include <linux/module.h>
> +#include <linux/mutex.h>
> +#include <linux/of_graph.h>
> +#include <linux/regulator/consumer.h>
> +#include <linux/slab.h>
> +
> +#include <media/v4l2-async.h>
> +#include <media/v4l2-ctrls.h>
> +#include <media/v4l2-device.h>
> +#include <media/v4l2-fwnode.h>
> +#include <media/v4l2-subdev.h>
> +
> +/* Register 0x00 */
> +#define MAX9286_MSTLINKSEL_AUTO		(7 << 5)
> +#define MAX9286_MSTLINKSEL(n)		((n) << 5)
> +#define MAX9286_EN_VS_GEN		BIT(4)
> +#define MAX9286_LINKEN(n)		(1 << (n))
> +/* Register 0x01 */
> +#define MAX9286_FSYNCMODE_ECU		(3 << 6)
> +#define MAX9286_FSYNCMODE_EXT		(2 << 6)
> +#define MAX9286_FSYNCMODE_INT_OUT	(1 << 6)
> +#define MAX9286_FSYNCMODE_INT_HIZ	(0 << 6)
> +#define MAX9286_GPIEN			BIT(5)
> +#define MAX9286_ENLMO_RSTFSYNC		BIT(2)
> +#define MAX9286_FSYNCMETH_AUTO		(2 << 0)
> +#define MAX9286_FSYNCMETH_SEMI_AUTO	(1 << 0)
> +#define MAX9286_FSYNCMETH_MANUAL	(0 << 0)
> +#define MAX9286_REG_FSYNC_PERIOD_L	0x06
> +#define MAX9286_REG_FSYNC_PERIOD_M	0x07
> +#define MAX9286_REG_FSYNC_PERIOD_H	0x08
> +/* Register 0x0a */
> +#define MAX9286_FWDCCEN(n)		(1 << ((n) + 4))
> +#define MAX9286_REVCCEN(n)		(1 << (n))
> +/* Register 0x0c */
> +#define MAX9286_HVEN			BIT(7)
> +#define MAX9286_EDC_6BIT_HAMMING	(2 << 5)
> +#define MAX9286_EDC_6BIT_CRC		(1 << 5)
> +#define MAX9286_EDC_1BIT_PARITY		(0 << 5)
> +#define MAX9286_DESEL			BIT(4)
> +#define MAX9286_INVVS			BIT(3)
> +#define MAX9286_INVHS			BIT(2)
> +#define MAX9286_HVSRC_D0		(2 << 0)
> +#define MAX9286_HVSRC_D14		(1 << 0)
> +#define MAX9286_HVSRC_D18		(0 << 0)
> +/* Register 0x0f */
> +#define MAX9286_0X0F_RESERVED		BIT(3)
> +/* Register 0x12 */
> +#define MAX9286_CSILANECNT(n)		(((n) - 1) << 6)
> +#define MAX9286_CSIDBL			BIT(5)
> +#define MAX9286_DBL			BIT(4)
> +#define MAX9286_DATATYPE_USER_8BIT	(11 << 0)
> +#define MAX9286_DATATYPE_USER_YUV_12BIT	(10 << 0)
> +#define MAX9286_DATATYPE_USER_24BIT	(9 << 0)
> +#define MAX9286_DATATYPE_RAW14		(8 << 0)
> +#define MAX9286_DATATYPE_RAW11		(7 << 0)
> +#define MAX9286_DATATYPE_RAW10		(6 << 0)
> +#define MAX9286_DATATYPE_RAW8		(5 << 0)
> +#define MAX9286_DATATYPE_YUV422_10BIT	(4 << 0)
> +#define MAX9286_DATATYPE_YUV422_8BIT	(3 << 0)
> +#define MAX9286_DATATYPE_RGB555		(2 << 0)
> +#define MAX9286_DATATYPE_RGB565		(1 << 0)
> +#define MAX9286_DATATYPE_RGB888		(0 << 0)
> +/* Register 0x15 */
> +#define MAX9286_VC(n)			((n) << 5)
> +#define MAX9286_VCTYPE			BIT(4)
> +#define MAX9286_CSIOUTEN		BIT(3)
> +#define MAX9286_0X15_RESV		(3 << 0)
> +/* Register 0x1b */
> +#define MAX9286_SWITCHIN(n)		(1 << ((n) + 4))
> +#define MAX9286_ENEQ(n)			(1 << (n))
> +/* Register 0x27 */
> +#define MAX9286_LOCKED			BIT(7)
> +/* Register 0x31 */
> +#define MAX9286_FSYNC_LOCKED		BIT(6)
> +/* Register 0x34 */
> +#define MAX9286_I2CLOCACK		BIT(7)
> +#define MAX9286_I2CSLVSH_1046NS_469NS	(3 << 5)
> +#define MAX9286_I2CSLVSH_938NS_352NS	(2 << 5)
> +#define MAX9286_I2CSLVSH_469NS_234NS	(1 << 5)
> +#define MAX9286_I2CSLVSH_352NS_117NS	(0 << 5)
> +#define MAX9286_I2CMSTBT_837KBPS	(7 << 2)
> +#define MAX9286_I2CMSTBT_533KBPS	(6 << 2)
> +#define MAX9286_I2CMSTBT_339KBPS	(5 << 2)
> +#define MAX9286_I2CMSTBT_173KBPS	(4 << 2)
> +#define MAX9286_I2CMSTBT_105KBPS	(3 << 2)
> +#define MAX9286_I2CMSTBT_84KBPS		(2 << 2)
> +#define MAX9286_I2CMSTBT_28KBPS		(1 << 2)
> +#define MAX9286_I2CMSTBT_8KBPS		(0 << 2)
> +#define MAX9286_I2CSLVTO_NONE		(3 << 0)
> +#define MAX9286_I2CSLVTO_1024US		(2 << 0)
> +#define MAX9286_I2CSLVTO_256US		(1 << 0)
> +#define MAX9286_I2CSLVTO_64US		(0 << 0)
> +/* Register 0x3b */
> +#define MAX9286_REV_TRF(n)		((n) << 4)
> +#define MAX9286_REV_AMP(n)		((((n) - 30) / 10) << 1) /* in mV */
> +#define MAX9286_REV_AMP_X		BIT(0)
> +/* Register 0x3f */
> +#define MAX9286_EN_REV_CFG		BIT(6)
> +#define MAX9286_REV_FLEN(n)		((n) - 20)
> +/* Register 0x49 */
> +#define MAX9286_VIDEO_DETECT_MASK	0x0f
> +/* Register 0x69 */
> +#define MAX9286_LFLTBMONMASKED		BIT(7)
> +#define MAX9286_LOCKMONMASKED		BIT(6)
> +#define MAX9286_AUTOCOMBACKEN		BIT(5)
> +#define MAX9286_AUTOMASKEN		BIT(4)
> +#define MAX9286_MASKLINK(n)		((n) << 0)
> +
> +/*
> + * The sink and source pads are created to match the OF graph port numbers so
> + * that their indexes can be used interchangeably.
> + */
> +#define MAX9286_NUM_GMSL		4
> +#define MAX9286_N_SINKS			4
> +#define MAX9286_N_PADS			5
> +#define MAX9286_SRC_PAD			4
> +
> +struct max9286_source {
> +	struct v4l2_async_subdev asd;
> +	struct v4l2_subdev *sd;
> +	struct fwnode_handle *fwnode;
> +};
> +
> +#define asd_to_max9286_source(_asd) \
> +	container_of(_asd, struct max9286_source, asd)
> +
> +struct max9286_priv {
> +	struct i2c_client *client;
> +	struct gpio_desc *gpiod_pwdn;
> +	struct v4l2_subdev sd;
> +	struct media_pad pads[MAX9286_N_PADS];
> +	struct regulator *regulator;
> +
> +	struct gpio_chip gpio;
> +	u8 gpio_state;
> +
> +	struct i2c_mux_core *mux;
> +	unsigned int mux_channel;
> +	bool mux_open;
> +
> +	struct v4l2_ctrl_handler ctrls;
> +	struct v4l2_ctrl *pixelrate;
> +
> +	struct v4l2_mbus_framefmt fmt[MAX9286_N_SINKS];
> +
> +	/* Protects controls and fmt structures */
> +	struct mutex mutex;
> +
> +	unsigned int nsources;
> +	unsigned int source_mask;
> +	unsigned int route_mask;
> +	unsigned int bound_sources;
> +	unsigned int csi2_data_lanes;
> +	struct max9286_source sources[MAX9286_NUM_GMSL];
> +	struct v4l2_async_notifier notifier;
> +};
> +
> +static struct max9286_source *next_source(struct max9286_priv *priv,
> +					  struct max9286_source *source)
> +{
> +	if (!source)
> +		source = &priv->sources[0];
> +	else
> +		source++;
> +
> +	for (; source < &priv->sources[MAX9286_NUM_GMSL]; source++) {
> +		if (source->fwnode)
> +			return source;
> +	}
> +
> +	return NULL;
> +}
> +
> +#define for_each_source(priv, source) \
> +	for ((source) = NULL; ((source) = next_source((priv), (source))); )
> +
> +#define to_index(priv, source) ((source) - &(priv)->sources[0])
> +
> +static inline struct max9286_priv *sd_to_max9286(struct v4l2_subdev *sd)
> +{
> +	return container_of(sd, struct max9286_priv, sd);
> +}
> +
> +/* -----------------------------------------------------------------------------
> + * I2C IO
> + */
> +
> +static int max9286_read(struct max9286_priv *priv, u8 reg)
> +{
> +	int ret;
> +
> +	ret = i2c_smbus_read_byte_data(priv->client, reg);
> +	if (ret < 0)
> +		dev_err(&priv->client->dev,
> +			"%s: register 0x%02x read failed (%d)\n",
> +			__func__, reg, ret);
> +
> +	return ret;
> +}
> +
> +static int max9286_write(struct max9286_priv *priv, u8 reg, u8 val)
> +{
> +	int ret;
> +
> +	ret = i2c_smbus_write_byte_data(priv->client, reg, val);
> +	if (ret < 0)
> +		dev_err(&priv->client->dev,
> +			"%s: register 0x%02x write failed (%d)\n",
> +			__func__, reg, ret);
> +
> +	return ret;
> +}
> +
> +/* -----------------------------------------------------------------------------
> + * I2C Multiplexer
> + */
> +
> +static void max9286_i2c_mux_configure(struct max9286_priv *priv, u8 conf)
> +{
> +	max9286_write(priv, 0x0a, conf);
> +
> +	/*
> +	 * We must sleep after any change to the forward or reverse channel
> +	 * configuration.
> +	 */
> +	usleep_range(3000, 5000);
> +}
> +
> +static void max9286_i2c_mux_open(struct max9286_priv *priv)
> +{
> +	/* Open all channels on the MAX9286 */
> +	max9286_i2c_mux_configure(priv, 0xff);
> +
> +	priv->mux_open = true;
> +}
> +
> +static void max9286_i2c_mux_close(struct max9286_priv *priv)
> +{
> +	/*
> +	 * Ensure that both the forward and reverse channel are disabled on the
> +	 * mux, and that the channel ID is invalidated to ensure we reconfigure
> +	 * on the next max9286_i2c_mux_select() call.
> +	 */
> +	max9286_i2c_mux_configure(priv, 0x00);
> +
> +	priv->mux_open = false;
> +	priv->mux_channel = -1;
> +}
> +
> +static int max9286_i2c_mux_select(struct i2c_mux_core *muxc, u32 chan)
> +{
> +	struct max9286_priv *priv = i2c_mux_priv(muxc);
> +
> +	/* Channel select is disabled when configured in the opened state. */
> +	if (priv->mux_open)
> +		return 0;
> +
> +	if (priv->mux_channel == chan)
> +		return 0;
> +
> +	priv->mux_channel = chan;
> +
> +	max9286_i2c_mux_configure(priv,
> +				  MAX9286_FWDCCEN(chan) |
> +				  MAX9286_REVCCEN(chan));
> +
> +	return 0;
> +}
> +
> +static int max9286_i2c_mux_init(struct max9286_priv *priv)
> +{
> +	struct max9286_source *source;
> +	int ret;
> +
> +	if (!i2c_check_functionality(priv->client->adapter,
> +				     I2C_FUNC_SMBUS_WRITE_BYTE_DATA))
> +		return -ENODEV;
> +
> +	priv->mux = i2c_mux_alloc(priv->client->adapter, &priv->client->dev,
> +				  priv->nsources, 0, I2C_MUX_LOCKED,
> +				  max9286_i2c_mux_select, NULL);
> +	if (!priv->mux)
> +		return -ENOMEM;
> +
> +	priv->mux->priv = priv;
> +
> +	for_each_source(priv, source) {
> +		unsigned int index = to_index(priv, source);
> +
> +		ret = i2c_mux_add_adapter(priv->mux, 0, index, 0);
> +		if (ret < 0)
> +			goto error;
> +	}
> +
> +	return 0;
> +
> +error:
> +	i2c_mux_del_adapters(priv->mux);
> +	return ret;
> +}
> +
> +static void max9286_configure_i2c(struct max9286_priv *priv, bool localack)
> +{
> +	u8 config = MAX9286_I2CSLVSH_469NS_234NS | MAX9286_I2CSLVTO_1024US |
> +		    MAX9286_I2CMSTBT_105KBPS;
> +
> +	if (localack)
> +		config |= MAX9286_I2CLOCACK;
> +
> +	max9286_write(priv, 0x34, config);
> +	usleep_range(3000, 5000);
> +}
> +
> +/*
> + * max9286_check_video_links() - Make sure video links are detected and locked
> + *
> + * Performs safety checks on video link status. Make sure they are detected
> + * and all enabled links are locked.
> + *
> + * Returns 0 for success, -EIO for errors.
> + */
> +static int max9286_check_video_links(struct max9286_priv *priv)
> +{
> +	unsigned int i;
> +	int ret;
> +
> +	/*
> +	 * Make sure valid video links are detected.
> +	 * The delay is not characterized in de-serializer manual, wait up
> +	 * to 5 ms.
> +	 */
> +	for (i = 0; i < 10; i++) {
> +		ret = max9286_read(priv, 0x49);
> +		if (ret < 0)
> +			return -EIO;
> +
> +		if ((ret & MAX9286_VIDEO_DETECT_MASK) == priv->source_mask)
> +			break;
> +
> +		usleep_range(350, 500);
> +	}
> +
> +	if (i == 10) {
> +		dev_err(&priv->client->dev,
> +			"Unable to detect video links: 0x%02x\n", ret);
> +		return -EIO;
> +	}
> +
> +	/* Make sure all enabled links are locked (4ms max). */
> +	for (i = 0; i < 10; i++) {
> +		ret = max9286_read(priv, 0x27);
> +		if (ret < 0)
> +			return -EIO;
> +
> +		if (ret & MAX9286_LOCKED)
> +			break;
> +
> +		usleep_range(350, 450);
> +	}
> +
> +	if (i == 10) {
> +		dev_err(&priv->client->dev, "Not all enabled links locked\n");
> +		return -EIO;
> +	}
> +
> +	return 0;
> +}
> +
> +/*
> + * max9286_check_config_link() - Detect and wait for configuration links
> + *
> + * Determine if the configuration channel is up and settled for a link.
> + *
> + * Returns 0 for success, -EIO for errors.
> + */
> +static int max9286_check_config_link(struct max9286_priv *priv,
> +				     unsigned int source_mask)
> +{
> +	unsigned int conflink_mask = (source_mask & 0x0f) << 4;
> +	unsigned int i;
> +	int ret;
> +
> +	/*
> +	 * Make sure requested configuration links are detected.
> +	 * The delay is not characterized in the chip manual: wait up
> +	 * to 5 milliseconds.
> +	 */
> +	for (i = 0; i < 10; i++) {
> +		ret = max9286_read(priv, 0x49) & 0xf0;
> +		if (ret < 0)
> +			return -EIO;
> +
> +		if (ret == conflink_mask)
> +			break;
> +
> +		usleep_range(350, 500);
> +	}
> +
> +	if (ret != conflink_mask) {
> +		dev_err(&priv->client->dev,
> +			"Unable to detect configuration links: 0x%02x expected 0x%02x\n",
> +			ret, conflink_mask);
> +		return -EIO;
> +	}
> +
> +	dev_info(&priv->client->dev,
> +		 "Successfully detected configuration links after %u loops: 0x%02x\n",
> +		 i, conflink_mask);
> +
> +	return 0;
> +}
> +
> +/* -----------------------------------------------------------------------------
> + * V4L2 Subdev
> + */
> +
> +static int max9286_set_pixelrate(struct max9286_priv *priv)
> +{
> +	struct max9286_source *source = NULL;
> +	u64 pixelrate = 0;
> +
> +	for_each_source(priv, source) {
> +		struct v4l2_ctrl *ctrl;
> +		u64 source_rate = 0;
> +
> +		/* Pixel rate is mandatory to be reported by sources. */
> +		ctrl = v4l2_ctrl_find(source->sd->ctrl_handler,
> +				      V4L2_CID_PIXEL_RATE);
> +		if (!ctrl) {
> +			pixelrate = 0;
> +			break;
> +		}
> +
> +		/* All source must report the same pixel rate. */
> +		source_rate = v4l2_ctrl_g_ctrl_int64(ctrl);
> +		if (!pixelrate) {
> +			pixelrate = source_rate;
> +		} else if (pixelrate != source_rate) {
> +			dev_err(&priv->client->dev,
> +				"Unable to calculate pixel rate\n");
> +			return -EINVAL;
> +		}
> +	}
> +
> +	if (!pixelrate) {
> +		dev_err(&priv->client->dev,
> +			"No pixel rate control available in sources\n");
> +		return -EINVAL;
> +	}
> +
> +	/*
> +	 * The CSI-2 transmitter pixel rate is the single source rate multiplied
> +	 * by the number of available sources.
> +	 */
> +	return v4l2_ctrl_s_ctrl_int64(priv->pixelrate,
> +				      pixelrate * priv->nsources);
> +}
> +
> +static int max9286_notify_bound(struct v4l2_async_notifier *notifier,
> +				struct v4l2_subdev *subdev,
> +				struct v4l2_async_subdev *asd)
> +{
> +	struct max9286_priv *priv = sd_to_max9286(notifier->sd);
> +	struct max9286_source *source = asd_to_max9286_source(asd);
> +	unsigned int index = to_index(priv, source);
> +	unsigned int src_pad;
> +	int ret;
> +
> +	ret = media_entity_get_fwnode_pad(&subdev->entity,
> +					  source->fwnode,
> +					  MEDIA_PAD_FL_SOURCE);
> +	if (ret < 0) {
> +		dev_err(&priv->client->dev,
> +			"Failed to find pad for %s\n", subdev->name);
> +		return ret;
> +	}
> +
> +	priv->bound_sources |= BIT(index);
> +	source->sd = subdev;
> +	src_pad = ret;
> +
> +	ret = media_create_pad_link(&source->sd->entity, src_pad,
> +				    &priv->sd.entity, index,
> +				    MEDIA_LNK_FL_ENABLED |
> +				    MEDIA_LNK_FL_IMMUTABLE);
> +	if (ret) {
> +		dev_err(&priv->client->dev,
> +			"Unable to link %s:%u -> %s:%u\n",
> +			source->sd->name, src_pad, priv->sd.name, index);
> +		return ret;
> +	}
> +
> +	dev_dbg(&priv->client->dev, "Bound %s pad: %u on index %u\n",
> +		subdev->name, src_pad, index);
> +
> +	/*
> +	 * We can only register v4l2_async_notifiers, which do not provide a
> +	 * means to register a complete callback. bound_sources allows us to
> +	 * identify when all remote serializers have completed their probe.
> +	 */
> +	if (priv->bound_sources != priv->source_mask)
> +		return 0;
> +
> +	/*
> +	 * All enabled sources have probed and enabled their reverse control
> +	 * channels:
> +	 *
> +	 * - Verify all configuration links are properly detected
> +	 * - Disable auto-ack as communication on the control channel are now
> +	 *   stable.
> +	 */
> +	max9286_check_config_link(priv, priv->source_mask);
> +
> +	/*
> +	 * Re-configure I2C with local acknowledge disabled after cameras have
> +	 * probed.
> +	 */
> +	max9286_configure_i2c(priv, false);
> +
> +	return max9286_set_pixelrate(priv);
> +}
> +
> +static void max9286_notify_unbind(struct v4l2_async_notifier *notifier,
> +				  struct v4l2_subdev *subdev,
> +				  struct v4l2_async_subdev *asd)
> +{
> +	struct max9286_priv *priv = sd_to_max9286(notifier->sd);
> +	struct max9286_source *source = asd_to_max9286_source(asd);
> +	unsigned int index = to_index(priv, source);
> +
> +	source->sd = NULL;
> +	priv->bound_sources &= ~BIT(index);
> +}
> +
> +static const struct v4l2_async_notifier_operations max9286_notify_ops = {
> +	.bound = max9286_notify_bound,
> +	.unbind = max9286_notify_unbind,
> +};
> +
> +static int max9286_v4l2_notifier_register(struct max9286_priv *priv)
> +{
> +	struct device *dev = &priv->client->dev;
> +	struct max9286_source *source = NULL;
> +	int ret;
> +
> +	if (!priv->nsources)
> +		return 0;
> +
> +	v4l2_async_notifier_init(&priv->notifier);
> +
> +	for_each_source(priv, source) {
> +		unsigned int i = to_index(priv, source);
> +
> +		source->asd.match_type = V4L2_ASYNC_MATCH_FWNODE;
> +		source->asd.match.fwnode = source->fwnode;
> +
> +		ret = v4l2_async_notifier_add_subdev(&priv->notifier,
> +						     &source->asd);
> +		if (ret) {
> +			dev_err(dev, "Failed to add subdev for source %d", i);
> +			v4l2_async_notifier_cleanup(&priv->notifier);
> +			return ret;
> +		}
> +
> +		/*
> +		 * Balance the reference counting handled through
> +		 * v4l2_async_notifier_cleanup()
> +		 */
> +		fwnode_handle_get(source->fwnode);
> +	}
> +
> +	priv->notifier.ops = &max9286_notify_ops;
> +
> +	ret = v4l2_async_subdev_notifier_register(&priv->sd, &priv->notifier);
> +	if (ret) {
> +		dev_err(dev, "Failed to register subdev_notifier");
> +		v4l2_async_notifier_cleanup(&priv->notifier);
> +		return ret;
> +	}
> +
> +	return 0;
> +}
> +
> +static void max9286_v4l2_notifier_unregister(struct max9286_priv *priv)
> +{
> +	if (!priv->nsources)
> +		return;
> +
> +	v4l2_async_notifier_unregister(&priv->notifier);
> +	v4l2_async_notifier_cleanup(&priv->notifier);
> +}
> +
> +static int max9286_s_stream(struct v4l2_subdev *sd, int enable)
> +{
> +	struct max9286_priv *priv = sd_to_max9286(sd);
> +	struct max9286_source *source;
> +	unsigned int i;
> +	bool sync = false;
> +	int ret;
> +
> +	if (enable) {
> +		/*
> +		 * The frame sync between cameras is transmitted across the
> +		 * reverse channel as GPIO. We must open all channels while
> +		 * streaming to allow this synchronisation signal to be shared.
> +		 */
> +		max9286_i2c_mux_open(priv);
> +
> +		/* Start all cameras. */
> +		for_each_source(priv, source) {
> +			ret = v4l2_subdev_call(source->sd, video, s_stream, 1);
> +			if (ret)
> +				return ret;
> +		}
> +
> +		ret = max9286_check_video_links(priv);
> +		if (ret)
> +			return ret;
> +
> +		/*
> +		 * Wait until frame synchronization is locked.
> +		 *
> +		 * Manual says frame sync locking should take ~6 VTS.
> +		 * From practical experience at least 8 are required. Give
> +		 * 12 complete frames time (~400ms at 30 fps) to achieve frame
> +		 * locking before returning error.
> +		 */
> +		for (i = 0; i < 40; i++) {
> +			if (max9286_read(priv, 0x31) & MAX9286_FSYNC_LOCKED) {
> +				sync = true;
> +				break;
> +			}
> +			usleep_range(9000, 11000);
> +		}
> +
> +		if (!sync) {
> +			dev_err(&priv->client->dev,
> +				"Failed to get frame synchronization\n");
> +			return -EXDEV; /* Invalid cross-device link */
> +		}
> +
> +		/*
> +		 * Enable CSI output, VC set according to link number.
> +		 * Bit 7 must be set (chip manual says it's 0 and reserved).
> +		 */
> +		max9286_write(priv, 0x15, 0x80 | MAX9286_VCTYPE |
> +			      MAX9286_CSIOUTEN | MAX9286_0X15_RESV);
> +	} else {
> +		max9286_write(priv, 0x15, MAX9286_VCTYPE | MAX9286_0X15_RESV);
> +
> +		/* Stop all cameras. */
> +		for_each_source(priv, source)
> +			v4l2_subdev_call(source->sd, video, s_stream, 0);
> +
> +		max9286_i2c_mux_close(priv);
> +	}
> +
> +	return 0;
> +}
> +
> +static int max9286_enum_mbus_code(struct v4l2_subdev *sd,
> +				  struct v4l2_subdev_pad_config *cfg,
> +				  struct v4l2_subdev_mbus_code_enum *code)
> +{
> +	if (code->pad || code->index > 0)
> +		return -EINVAL;
> +
> +	code->code = MEDIA_BUS_FMT_UYVY8_2X8;
> +
> +	return 0;
> +}
> +
> +static struct v4l2_mbus_framefmt *
> +max9286_get_pad_format(struct max9286_priv *priv,
> +		       struct v4l2_subdev_pad_config *cfg,
> +		       unsigned int pad, u32 which)
> +{
> +	switch (which) {
> +	case V4L2_SUBDEV_FORMAT_TRY:
> +		return v4l2_subdev_get_try_format(&priv->sd, cfg, pad);
> +	case V4L2_SUBDEV_FORMAT_ACTIVE:
> +		return &priv->fmt[pad];
> +	default:
> +		return NULL;
> +	}
> +}
> +
> +static int max9286_set_fmt(struct v4l2_subdev *sd,
> +			   struct v4l2_subdev_pad_config *cfg,
> +			   struct v4l2_subdev_format *format)
> +{
> +	struct max9286_priv *priv = sd_to_max9286(sd);
> +	struct v4l2_mbus_framefmt *cfg_fmt;
> +
> +	if (format->pad >= MAX9286_SRC_PAD)
> +		return -EINVAL;
> +
> +	/* Refuse non YUV422 formats as we hardcode DT to 8 bit YUV422 */
> +	switch (format->format.code) {
> +	case MEDIA_BUS_FMT_UYVY8_2X8:
> +	case MEDIA_BUS_FMT_VYUY8_2X8:
> +	case MEDIA_BUS_FMT_YUYV8_2X8:
> +	case MEDIA_BUS_FMT_YVYU8_2X8:
> +		break;
> +	default:
> +		format->format.code = MEDIA_BUS_FMT_YUYV8_2X8;

Is there any reason for not setting default format to MEDIA_BUS_FMT_UYVY8_2X8?

Thanks,
Mani

> +		break;
> +	}
> +
> +	cfg_fmt = max9286_get_pad_format(priv, cfg, format->pad, format->which);
> +	if (!cfg_fmt)
> +		return -EINVAL;
> +
> +	mutex_lock(&priv->mutex);
> +	*cfg_fmt = format->format;
> +	mutex_unlock(&priv->mutex);
> +
> +	return 0;
> +}
> +
> +static int max9286_get_fmt(struct v4l2_subdev *sd,
> +			   struct v4l2_subdev_pad_config *cfg,
> +			   struct v4l2_subdev_format *format)
> +{
> +	struct max9286_priv *priv = sd_to_max9286(sd);
> +	struct v4l2_mbus_framefmt *cfg_fmt;
> +
> +	if (format->pad >= MAX9286_SRC_PAD)
> +		return -EINVAL;
> +
> +	cfg_fmt = max9286_get_pad_format(priv, cfg, format->pad, format->which);
> +	if (!cfg_fmt)
> +		return -EINVAL;
> +
> +	mutex_lock(&priv->mutex);
> +	format->format = *cfg_fmt;
> +	mutex_unlock(&priv->mutex);
> +
> +	return 0;
> +}
> +
> +static const struct v4l2_subdev_video_ops max9286_video_ops = {
> +	.s_stream	= max9286_s_stream,
> +};
> +
> +static const struct v4l2_subdev_pad_ops max9286_pad_ops = {
> +	.enum_mbus_code = max9286_enum_mbus_code,
> +	.get_fmt	= max9286_get_fmt,
> +	.set_fmt	= max9286_set_fmt,
> +};
> +
> +static const struct v4l2_subdev_ops max9286_subdev_ops = {
> +	.video		= &max9286_video_ops,
> +	.pad		= &max9286_pad_ops,
> +};
> +
> +static void max9286_init_format(struct v4l2_mbus_framefmt *fmt)
> +{
> +	fmt->width		= 1280;
> +	fmt->height		= 800;
> +	fmt->code		= MEDIA_BUS_FMT_UYVY8_2X8;
> +	fmt->colorspace		= V4L2_COLORSPACE_SRGB;
> +	fmt->field		= V4L2_FIELD_NONE;
> +	fmt->ycbcr_enc		= V4L2_YCBCR_ENC_DEFAULT;
> +	fmt->quantization	= V4L2_QUANTIZATION_DEFAULT;
> +	fmt->xfer_func		= V4L2_XFER_FUNC_DEFAULT;
> +}
> +
> +static int max9286_open(struct v4l2_subdev *subdev, struct v4l2_subdev_fh *fh)
> +{
> +	struct v4l2_mbus_framefmt *format;
> +	unsigned int i;
> +
> +	for (i = 0; i < MAX9286_N_SINKS; i++) {
> +		format = v4l2_subdev_get_try_format(subdev, fh->pad, i);
> +		max9286_init_format(format);
> +	}
> +
> +	return 0;
> +}
> +
> +static const struct v4l2_subdev_internal_ops max9286_subdev_internal_ops = {
> +	.open = max9286_open,
> +};
> +
> +static int max9286_s_ctrl(struct v4l2_ctrl *ctrl)
> +{
> +	switch (ctrl->id) {
> +	case V4L2_CID_PIXEL_RATE:
> +		return 0;
> +	default:
> +		return -EINVAL;
> +	}
> +}
> +
> +static const struct v4l2_ctrl_ops max9286_ctrl_ops = {
> +	.s_ctrl	= max9286_s_ctrl,
> +};
> +
> +static int max9286_v4l2_register(struct max9286_priv *priv)
> +{
> +	struct device *dev = &priv->client->dev;
> +	struct fwnode_handle *ep;
> +	int ret;
> +	int i;
> +
> +	/* Register v4l2 async notifiers for connected Camera subdevices */
> +	ret = max9286_v4l2_notifier_register(priv);
> +	if (ret) {
> +		dev_err(dev, "Unable to register V4L2 async notifiers\n");
> +		return ret;
> +	}
> +
> +	/* Configure V4L2 for the MAX9286 itself */
> +
> +	for (i = 0; i < MAX9286_N_SINKS; i++)
> +		max9286_init_format(&priv->fmt[i]);
> +
> +	v4l2_i2c_subdev_init(&priv->sd, priv->client, &max9286_subdev_ops);
> +	priv->sd.internal_ops = &max9286_subdev_internal_ops;
> +	priv->sd.flags |= V4L2_SUBDEV_FL_HAS_DEVNODE;
> +
> +	v4l2_ctrl_handler_init(&priv->ctrls, 1);
> +	priv->pixelrate = v4l2_ctrl_new_std(&priv->ctrls,
> +					    &max9286_ctrl_ops,
> +					    V4L2_CID_PIXEL_RATE,
> +					    1, INT_MAX, 1, 50000000);
> +
> +	priv->sd.ctrl_handler = &priv->ctrls;
> +	ret = priv->ctrls.error;
> +	if (ret)
> +		goto err_async;
> +
> +	priv->sd.entity.function = MEDIA_ENT_F_VID_IF_BRIDGE;
> +
> +	priv->pads[MAX9286_SRC_PAD].flags = MEDIA_PAD_FL_SOURCE;
> +	for (i = 0; i < MAX9286_SRC_PAD; i++)
> +		priv->pads[i].flags = MEDIA_PAD_FL_SINK;
> +	ret = media_entity_pads_init(&priv->sd.entity, MAX9286_N_PADS,
> +				     priv->pads);
> +	if (ret)
> +		goto err_async;
> +
> +	ep = fwnode_graph_get_endpoint_by_id(dev_fwnode(dev), MAX9286_SRC_PAD,
> +					     0, 0);
> +	if (!ep) {
> +		dev_err(dev, "Unable to retrieve endpoint on \"port@4\"\n");
> +		ret = -ENOENT;
> +		goto err_async;
> +	}
> +	priv->sd.fwnode = ep;
> +
> +	ret = v4l2_async_register_subdev(&priv->sd);
> +	if (ret < 0) {
> +		dev_err(dev, "Unable to register subdevice\n");
> +		goto err_put_node;
> +	}
> +
> +	return 0;
> +
> +err_put_node:
> +	fwnode_handle_put(ep);
> +err_async:
> +	max9286_v4l2_notifier_unregister(priv);
> +
> +	return ret;
> +}
> +
> +static void max9286_v4l2_unregister(struct max9286_priv *priv)
> +{
> +	fwnode_handle_put(priv->sd.fwnode);
> +	v4l2_async_unregister_subdev(&priv->sd);
> +	max9286_v4l2_notifier_unregister(priv);
> +}
> +
> +/* -----------------------------------------------------------------------------
> + * Probe/Remove
> + */
> +
> +static int max9286_setup(struct max9286_priv *priv)
> +{
> +	/*
> +	 * Link ordering values for all enabled links combinations. Orders must
> +	 * be assigned sequentially from 0 to the number of enabled links
> +	 * without leaving any hole for disabled links. We thus assign orders to
> +	 * enabled links first, and use the remaining order values for disabled
> +	 * links are all links must have a different order value;
> +	 */
> +	static const u8 link_order[] = {
> +		(3 << 6) | (2 << 4) | (1 << 2) | (0 << 0), /* xxxx */
> +		(3 << 6) | (2 << 4) | (1 << 2) | (0 << 0), /* xxx0 */
> +		(3 << 6) | (2 << 4) | (0 << 2) | (1 << 0), /* xx0x */
> +		(3 << 6) | (2 << 4) | (1 << 2) | (0 << 0), /* xx10 */
> +		(3 << 6) | (0 << 4) | (2 << 2) | (1 << 0), /* x0xx */
> +		(3 << 6) | (1 << 4) | (2 << 2) | (0 << 0), /* x1x0 */
> +		(3 << 6) | (1 << 4) | (0 << 2) | (2 << 0), /* x10x */
> +		(3 << 6) | (1 << 4) | (1 << 2) | (0 << 0), /* x210 */
> +		(0 << 6) | (3 << 4) | (2 << 2) | (1 << 0), /* 0xxx */
> +		(1 << 6) | (3 << 4) | (2 << 2) | (0 << 0), /* 1xx0 */
> +		(1 << 6) | (3 << 4) | (0 << 2) | (2 << 0), /* 1x0x */
> +		(2 << 6) | (3 << 4) | (1 << 2) | (0 << 0), /* 2x10 */
> +		(1 << 6) | (0 << 4) | (3 << 2) | (2 << 0), /* 10xx */
> +		(2 << 6) | (1 << 4) | (3 << 2) | (0 << 0), /* 21x0 */
> +		(2 << 6) | (1 << 4) | (0 << 2) | (3 << 0), /* 210x */
> +		(3 << 6) | (2 << 4) | (1 << 2) | (0 << 0), /* 3210 */
> +	};
> +
> +	/*
> +	 * Set the I2C bus speed.
> +	 *
> +	 * Enable I2C Local Acknowledge during the probe sequences of the camera
> +	 * only. This should be disabled after the mux is initialised.
> +	 */
> +	max9286_configure_i2c(priv, true);
> +
> +	/*
> +	 * Reverse channel setup.
> +	 *
> +	 * - Enable custom reverse channel configuration (through register 0x3f)
> +	 *   and set the first pulse length to 35 clock cycles.
> +	 * - Increase the reverse channel amplitude to 170mV to accommodate the
> +	 *   high threshold enabled by the serializer driver.
> +	 */
> +	max9286_write(priv, 0x3f, MAX9286_EN_REV_CFG | MAX9286_REV_FLEN(35));
> +	max9286_write(priv, 0x3b, MAX9286_REV_TRF(1) | MAX9286_REV_AMP(70) |
> +		      MAX9286_REV_AMP_X);
> +	usleep_range(2000, 2500);
> +
> +	/*
> +	 * Enable GMSL links, mask unused ones and autodetect link
> +	 * used as CSI clock source.
> +	 */
> +	max9286_write(priv, 0x00, MAX9286_MSTLINKSEL_AUTO | priv->route_mask);
> +	max9286_write(priv, 0x0b, link_order[priv->route_mask]);
> +	max9286_write(priv, 0x69, (0xf & ~priv->route_mask));
> +
> +	/*
> +	 * Video format setup:
> +	 * Disable CSI output, VC is set according to Link number.
> +	 */
> +	max9286_write(priv, 0x15, MAX9286_VCTYPE | MAX9286_0X15_RESV);
> +
> +	/* Enable CSI-2 Lane D0-D3 only, DBL mode, YUV422 8-bit. */
> +	max9286_write(priv, 0x12, MAX9286_CSIDBL | MAX9286_DBL |
> +		      MAX9286_CSILANECNT(priv->csi2_data_lanes) |
> +		      MAX9286_DATATYPE_YUV422_8BIT);
> +
> +	/* Automatic: FRAMESYNC taken from the slowest Link. */
> +	max9286_write(priv, 0x01, MAX9286_FSYNCMODE_INT_HIZ |
> +		      MAX9286_FSYNCMETH_AUTO);
> +
> +	/* Enable HS/VS encoding, use D14/15 for HS/VS, invert VS. */
> +	max9286_write(priv, 0x0c, MAX9286_HVEN | MAX9286_INVVS |
> +		      MAX9286_HVSRC_D14);
> +
> +	/*
> +	 * The overlap window seems to provide additional validation by tracking
> +	 * the delay between vsync and frame sync, generating an error if the
> +	 * delay is bigger than the programmed window, though it's not yet clear
> +	 * what value should be set.
> +	 *
> +	 * As it's an optional value and can be disabled, we do so by setting
> +	 * a 0 overlap value.
> +	 */
> +	max9286_write(priv, 0x63, 0);
> +	max9286_write(priv, 0x64, 0);
> +
> +	/*
> +	 * Wait for 2ms to allow the link to resynchronize after the
> +	 * configuration change.
> +	 */
> +	usleep_range(2000, 5000);
> +
> +	return 0;
> +}
> +
> +static void max9286_gpio_set(struct gpio_chip *chip,
> +			     unsigned int offset, int value)
> +{
> +	struct max9286_priv *priv = gpiochip_get_data(chip);
> +
> +	if (value)
> +		priv->gpio_state |= BIT(offset);
> +	else
> +		priv->gpio_state &= ~BIT(offset);
> +
> +	max9286_write(priv, 0x0f, MAX9286_0X0F_RESERVED | priv->gpio_state);
> +}
> +
> +static int max9286_gpio_get(struct gpio_chip *chip, unsigned int offset)
> +{
> +	struct max9286_priv *priv = gpiochip_get_data(chip);
> +
> +	return priv->gpio_state & BIT(offset);
> +}
> +
> +static int max9286_register_gpio(struct max9286_priv *priv)
> +{
> +	struct device *dev = &priv->client->dev;
> +	struct gpio_chip *gpio = &priv->gpio;
> +	int ret;
> +
> +	static const char * const names[] = {
> +		"GPIO0OUT",
> +		"GPIO1OUT",
> +	};
> +
> +	/* Configure the GPIO */
> +	gpio->label = dev_name(dev);
> +	gpio->parent = dev;
> +	gpio->owner = THIS_MODULE;
> +	gpio->of_node = dev->of_node;
> +	gpio->ngpio = 2;
> +	gpio->base = -1;
> +	gpio->set = max9286_gpio_set;
> +	gpio->get = max9286_gpio_get;
> +	gpio->can_sleep = true;
> +	gpio->names = names;
> +
> +	/* GPIO values default to high */
> +	priv->gpio_state = BIT(0) | BIT(1);
> +
> +	ret = devm_gpiochip_add_data(dev, gpio, priv);
> +	if (ret)
> +		dev_err(dev, "Unable to create gpio_chip\n");
> +
> +	return ret;
> +}
> +
> +static int max9286_init(struct device *dev)
> +{
> +	struct max9286_priv *priv;
> +	struct i2c_client *client;
> +	int ret;
> +
> +	client = to_i2c_client(dev);
> +	priv = i2c_get_clientdata(client);
> +
> +	/* Enable the bus power. */
> +	ret = regulator_enable(priv->regulator);
> +	if (ret < 0) {
> +		dev_err(&client->dev, "Unable to turn PoC on\n");
> +		return ret;
> +	}
> +
> +	ret = max9286_setup(priv);
> +	if (ret) {
> +		dev_err(dev, "Unable to setup max9286\n");
> +		goto err_regulator;
> +	}
> +
> +	/*
> +	 * Register all V4L2 interactions for the MAX9286 and notifiers for
> +	 * any subdevices connected.
> +	 */
> +	ret = max9286_v4l2_register(priv);
> +	if (ret) {
> +		dev_err(dev, "Failed to register with V4L2\n");
> +		goto err_regulator;
> +	}
> +
> +	ret = max9286_i2c_mux_init(priv);
> +	if (ret) {
> +		dev_err(dev, "Unable to initialize I2C multiplexer\n");
> +		goto err_v4l2_register;
> +	}
> +
> +	/* Leave the mux channels disabled until they are selected. */
> +	max9286_i2c_mux_close(priv);
> +
> +	return 0;
> +
> +err_v4l2_register:
> +	max9286_v4l2_unregister(priv);
> +err_regulator:
> +	regulator_disable(priv->regulator);
> +
> +	return ret;
> +}
> +
> +static void max9286_cleanup_dt(struct max9286_priv *priv)
> +{
> +	struct max9286_source *source;
> +
> +	for_each_source(priv, source) {
> +		fwnode_handle_put(source->fwnode);
> +		source->fwnode = NULL;
> +	}
> +}
> +
> +static int max9286_parse_dt(struct max9286_priv *priv)
> +{
> +	struct device *dev = &priv->client->dev;
> +	struct device_node *i2c_mux;
> +	struct device_node *node = NULL;
> +	unsigned int i2c_mux_mask = 0;
> +
> +	of_node_get(dev->of_node);
> +	i2c_mux = of_find_node_by_name(dev->of_node, "i2c-mux");
> +	if (!i2c_mux) {
> +		dev_err(dev, "Failed to find i2c-mux node\n");
> +		of_node_put(dev->of_node);
> +		return -EINVAL;
> +	}
> +
> +	/* Identify which i2c-mux channels are enabled */
> +	for_each_child_of_node(i2c_mux, node) {
> +		u32 id = 0;
> +
> +		of_property_read_u32(node, "reg", &id);
> +		if (id >= MAX9286_NUM_GMSL)
> +			continue;
> +
> +		if (!of_device_is_available(node)) {
> +			dev_dbg(dev, "Skipping disabled I2C bus port %u\n", id);
> +			continue;
> +		}
> +
> +		i2c_mux_mask |= BIT(id);
> +	}
> +	of_node_put(node);
> +	of_node_put(i2c_mux);
> +
> +	/* Parse the endpoints */
> +	for_each_endpoint_of_node(dev->of_node, node) {
> +		struct max9286_source *source;
> +		struct of_endpoint ep;
> +
> +		of_graph_parse_endpoint(node, &ep);
> +		dev_dbg(dev, "Endpoint %pOF on port %d",
> +			ep.local_node, ep.port);
> +
> +		if (ep.port > MAX9286_NUM_GMSL) {
> +			dev_err(dev, "Invalid endpoint %s on port %d",
> +				of_node_full_name(ep.local_node), ep.port);
> +			continue;
> +		}
> +
> +		/* For the source endpoint just parse the bus configuration. */
> +		if (ep.port == MAX9286_SRC_PAD) {
> +			struct v4l2_fwnode_endpoint vep = {
> +				.bus_type = V4L2_MBUS_CSI2_DPHY
> +			};
> +			int ret;
> +
> +			ret = v4l2_fwnode_endpoint_parse(
> +					of_fwnode_handle(node), &vep);
> +			if (ret) {
> +				of_node_put(node);
> +				of_node_put(dev->of_node);
> +				return ret;
> +			}
> +
> +			if (vep.bus_type != V4L2_MBUS_CSI2_DPHY) {
> +				dev_err(dev,
> +					"Media bus %u type not supported\n",
> +					vep.bus_type);
> +				v4l2_fwnode_endpoint_free(&vep);
> +				of_node_put(node);
> +				of_node_put(dev->of_node);
> +				return -EINVAL;
> +			}
> +
> +			priv->csi2_data_lanes =
> +				vep.bus.mipi_csi2.num_data_lanes;
> +			v4l2_fwnode_endpoint_free(&vep);
> +
> +			continue;
> +		}
> +
> +		/* Skip if the corresponding GMSL link is unavailable. */
> +		if (!(i2c_mux_mask & BIT(ep.port)))
> +			continue;
> +
> +		if (priv->sources[ep.port].fwnode) {
> +			dev_err(dev,
> +				"Multiple port endpoints are not supported: %d",
> +				ep.port);
> +
> +			continue;
> +		}
> +
> +		source = &priv->sources[ep.port];
> +		source->fwnode = fwnode_graph_get_remote_endpoint(
> +						of_fwnode_handle(node));
> +		if (!source->fwnode) {
> +			dev_err(dev,
> +				"Endpoint %pOF has no remote endpoint connection\n",
> +				ep.local_node);
> +
> +			continue;
> +		}
> +
> +		priv->source_mask |= BIT(ep.port);
> +		priv->nsources++;
> +	}
> +	of_node_put(node);
> +	of_node_put(dev->of_node);
> +
> +	priv->route_mask = priv->source_mask;
> +
> +	return 0;
> +}
> +
> +static int max9286_probe(struct i2c_client *client)
> +{
> +	struct max9286_priv *priv;
> +	int ret;
> +
> +	priv = devm_kzalloc(&client->dev, sizeof(*priv), GFP_KERNEL);
> +	if (!priv)
> +		return -ENOMEM;
> +
> +	mutex_init(&priv->mutex);
> +
> +	priv->client = client;
> +	i2c_set_clientdata(client, priv);
> +
> +	priv->gpiod_pwdn = devm_gpiod_get_optional(&client->dev, "enable",
> +						   GPIOD_OUT_HIGH);
> +	if (IS_ERR(priv->gpiod_pwdn))
> +		return PTR_ERR(priv->gpiod_pwdn);
> +
> +	gpiod_set_consumer_name(priv->gpiod_pwdn, "max9286-pwdn");
> +	gpiod_set_value_cansleep(priv->gpiod_pwdn, 1);
> +
> +	/* Wait at least 4ms before the I2C lines latch to the address */
> +	if (priv->gpiod_pwdn)
> +		usleep_range(4000, 5000);
> +
> +	/*
> +	 * The MAX9286 starts by default with all ports enabled, we disable all
> +	 * ports early to ensure that all channels are disabled if we error out
> +	 * and keep the bus consistent.
> +	 */
> +	max9286_i2c_mux_close(priv);
> +
> +	/*
> +	 * The MAX9286 initialises with auto-acknowledge enabled by default.
> +	 * This can be invasive to other transactions on the same bus, so
> +	 * disable it early. It will be enabled only as and when needed.
> +	 */
> +	max9286_configure_i2c(priv, false);
> +
> +	ret = max9286_register_gpio(priv);
> +	if (ret)
> +		goto err_powerdown;
> +
> +	priv->regulator = devm_regulator_get(&client->dev, "poc");
> +	if (IS_ERR(priv->regulator)) {
> +		if (PTR_ERR(priv->regulator) != -EPROBE_DEFER)
> +			dev_err(&client->dev,
> +				"Unable to get PoC regulator (%ld)\n",
> +				PTR_ERR(priv->regulator));
> +		ret = PTR_ERR(priv->regulator);
> +		goto err_powerdown;
> +	}
> +
> +	ret = max9286_parse_dt(priv);
> +	if (ret)
> +		goto err_powerdown;
> +
> +	ret = max9286_init(&client->dev);
> +	if (ret < 0)
> +		goto err_cleanup_dt;
> +
> +	return 0;
> +
> +err_cleanup_dt:
> +	max9286_cleanup_dt(priv);
> +err_powerdown:
> +	gpiod_set_value_cansleep(priv->gpiod_pwdn, 0);
> +
> +	return ret;
> +}
> +
> +static int max9286_remove(struct i2c_client *client)
> +{
> +	struct max9286_priv *priv = i2c_get_clientdata(client);
> +
> +	i2c_mux_del_adapters(priv->mux);
> +
> +	max9286_v4l2_unregister(priv);
> +
> +	regulator_disable(priv->regulator);
> +
> +	gpiod_set_value_cansleep(priv->gpiod_pwdn, 0);
> +
> +	max9286_cleanup_dt(priv);
> +
> +	return 0;
> +}
> +
> +static const struct of_device_id max9286_dt_ids[] = {
> +	{ .compatible = "maxim,max9286" },
> +	{},
> +};
> +MODULE_DEVICE_TABLE(of, max9286_dt_ids);
> +
> +static struct i2c_driver max9286_i2c_driver = {
> +	.driver	= {
> +		.name		= "max9286",
> +		.of_match_table	= of_match_ptr(max9286_dt_ids),
> +	},
> +	.probe_new	= max9286_probe,
> +	.remove		= max9286_remove,
> +};
> +
> +module_i2c_driver(max9286_i2c_driver);
> +
> +MODULE_DESCRIPTION("Maxim MAX9286 GMSL Deserializer Driver");
> +MODULE_AUTHOR("Jacopo Mondi, Kieran Bingham, Laurent Pinchart, Niklas S?derlund, Vladimir Barinov");
> +MODULE_LICENSE("GPL");
> -- 
> 2.25.1
>