Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Sat, 14 Dec 2019 00:38:16 +0200
From:   Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To:     Hsin-Yi Wang <hsinyi@chromium.org>
Cc:     dri-devel@lists.freedesktop.org, David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Nicolas Boichat <drinkcat@chromium.org>,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
        Andrzej Hajda <a.hajda@samsung.com>,
        Neil Armstrong <narmstrong@baylibre.com>,
        Jonas Karlman <jonas@kwiboo.se>,
        Jernej Skrabec <jernej.skrabec@siol.net>,
        p.zabel@pengutronix.de,
        Enric Balletbo i Serra <enric.balletbo@collabora.com>,
        Matthias Brugger <mbrugger@suse.com>,
        Russell King <rmk+kernel@arm.linux.org.uk>
Subject: Re: [PATCH RESEND 2/4] drm: bridge: anx7688: Add anx7688 bridge
 driver support.
Message-ID: <20191213223816.GS4860@pendragon.ideasonboard.com>
References: <20191211061911.238393-1-hsinyi@chromium.org>
 <20191211061911.238393-3-hsinyi@chromium.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <20191211061911.238393-3-hsinyi@chromium.org>
User-Agent: Mutt/1.10.1 (2018-07-13)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Hi Hsin-Yi and Nicolas,

Thank you for the patch.

On Wed, Dec 11, 2019 at 02:19:09PM +0800, Hsin-Yi Wang wrote:
> From: Nicolas Boichat <drinkcat@chromium.org>
> 
> ANX7688 is a HDMI to DP converter (as well as USB-C port controller),
> that has an internal microcontroller.
> 
> The only reason a Linux kernel driver is necessary is to reject
> resolutions that require more bandwidth than what is available on
> the DP side. DP bandwidth and lane count are reported by the bridge
> via 2 registers on I2C.

How about power, doesn't this chip have power supplies that potentially
need to be controlled ?

> Signed-off-by: Nicolas Boichat <drinkcat@chromium.org>
> Signed-off-by: Hsin-Yi Wang <hsinyi@chromium.org>
> ---
>  drivers/gpu/drm/bridge/Kconfig            |   9 +
>  drivers/gpu/drm/bridge/Makefile           |   1 +
>  drivers/gpu/drm/bridge/analogix-anx7688.c | 202 ++++++++++++++++++++++
>  3 files changed, 212 insertions(+)
>  create mode 100644 drivers/gpu/drm/bridge/analogix-anx7688.c
> 
> diff --git a/drivers/gpu/drm/bridge/Kconfig b/drivers/gpu/drm/bridge/Kconfig
> index 34362976cd6f..1f3fc6bec842 100644
> --- a/drivers/gpu/drm/bridge/Kconfig
> +++ b/drivers/gpu/drm/bridge/Kconfig
> @@ -16,6 +16,15 @@ config DRM_PANEL_BRIDGE
>  menu "Display Interface Bridges"
>  	depends on DRM && DRM_BRIDGE
>  
> +config DRM_ANALOGIX_ANX7688
> +	tristate "Analogix ANX7688 bridge"
> +	select DRM_KMS_HELPER
> +	select REGMAP_I2C
> +	---help---
> +	  ANX7688 is a transmitter to support DisplayPort over USB-C for
> +	  smartphone and tablets.
> +	  This driver only supports the HDMI to DP component of the chip.
> +
>  config DRM_ANALOGIX_ANX78XX
>  	tristate "Analogix ANX78XX bridge"
>  	select DRM_KMS_HELPER
> diff --git a/drivers/gpu/drm/bridge/Makefile b/drivers/gpu/drm/bridge/Makefile
> index 4934fcf5a6f8..7a1e0ec032e6 100644
> --- a/drivers/gpu/drm/bridge/Makefile
> +++ b/drivers/gpu/drm/bridge/Makefile
> @@ -1,4 +1,5 @@
>  # SPDX-License-Identifier: GPL-2.0
> +obj-$(CONFIG_DRM_ANALOGIX_ANX7688) += analogix-anx7688.o
>  obj-$(CONFIG_DRM_ANALOGIX_ANX78XX) += analogix-anx78xx.o
>  obj-$(CONFIG_DRM_CDNS_DSI) += cdns-dsi.o
>  obj-$(CONFIG_DRM_DUMB_VGA_DAC) += dumb-vga-dac.o
> diff --git a/drivers/gpu/drm/bridge/analogix-anx7688.c b/drivers/gpu/drm/bridge/analogix-anx7688.c
> new file mode 100644
> index 000000000000..baaed48d6201
> --- /dev/null
> +++ b/drivers/gpu/drm/bridge/analogix-anx7688.c
> @@ -0,0 +1,202 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * ANX7688 HDMI->DP bridge driver
> + *
> + * Copyright 2016 Google LLC
> + */
> +
> +#include <linux/i2c.h>
> +#include <linux/module.h>
> +#include <linux/regmap.h>
> +#include <drm/drm_bridge.h>
> +
> +/* Register addresses */
> +#define VENDOR_ID_REG 0x00
> +#define DEVICE_ID_REG 0x02
> +
> +#define FW_VERSION_REG 0x80
> +
> +#define DP_BANDWIDTH_REG 0x85
> +#define DP_LANE_COUNT_REG 0x86

Are these registers defined by the ANX7688 hardware, or by the firmware
running on the chip (and, I assume, developed by Google) ?

> +
> +#define VENDOR_ID 0x1f29
> +#define DEVICE_ID 0x7688
> +
> +/* First supported firmware version (0.85) */
> +#define MINIMUM_FW_VERSION 0x0085
> +
> +struct anx7688 {
> +	struct drm_bridge bridge;
> +	struct i2c_client *client;
> +	struct regmap *regmap;
> +
> +	bool filter;
> +};
> +
> +static inline struct anx7688 *bridge_to_anx7688(struct drm_bridge *bridge)
> +{
> +	return container_of(bridge, struct anx7688, bridge);
> +}
> +
> +static bool anx7688_bridge_mode_fixup(struct drm_bridge *bridge,
> +				      const struct drm_display_mode *mode,
> +				      struct drm_display_mode *adjusted_mode)
> +{
> +	struct anx7688 *anx7688 = bridge_to_anx7688(bridge);
> +	u8 regs[2];
> +	u8 dpbw, lanecount;
> +	int totalbw, requiredbw;
> +	int ret;
> +
> +	if (!anx7688->filter)
> +		return true;
> +
> +	/* Read both regs 0x85 (bandwidth) and 0x86 (lane count). */
> +	ret = regmap_bulk_read(anx7688->regmap, DP_BANDWIDTH_REG, regs, 2);
> +	if (ret < 0) {
> +		dev_err(&anx7688->client->dev,
> +			"Failed to read bandwidth/lane count\n");
> +		return false;
> +	}
> +	dpbw = regs[0];
> +	lanecount = regs[1];
> +
> +	/* Maximum 0x19 bandwidth (6.75 Gbps Turbo mode), 2 lanes */
> +	if (dpbw > 0x19 || lanecount > 2) {
> +		dev_err(&anx7688->client->dev,
> +			"Invalid bandwidth/lane count (%02x/%d)\n",
> +			dpbw, lanecount);
> +		return false;
> +	}
> +
> +	/* Compute available bandwidth (kHz) */
> +	totalbw = dpbw * lanecount * 270000 * 8 / 10;
> +
> +	/* Required bandwidth (8 bpc, kHz) */
> +	requiredbw = mode->clock * 8 * 3;
> +
> +	dev_dbg(&anx7688->client->dev,
> +		"DP bandwidth: %d kHz (%02x/%d); mode requires %d Khz\n",
> +		totalbw, dpbw, lanecount, requiredbw);
> +
> +	if (totalbw == 0) {
> +		dev_warn(&anx7688->client->dev,
> +			 "Bandwidth/lane count are 0, not rejecting modes\n");
> +		return true;
> +	}
> +
> +	return totalbw >= requiredbw;
> +}
> +
> +static const struct drm_bridge_funcs anx7688_bridge_funcs = {
> +	.mode_fixup	= anx7688_bridge_mode_fixup,
> +};
> +
> +static const struct regmap_config anx7688_regmap_config = {
> +	.reg_bits = 8,
> +	.val_bits = 8,
> +};
> +
> +static int anx7688_i2c_probe(struct i2c_client *client,
> +			     const struct i2c_device_id *id)
> +{
> +	struct anx7688 *anx7688;
> +	struct device *dev = &client->dev;
> +	int ret;
> +	u8 buffer[4];
> +	u16 vendor, device, fwversion;
> +
> +	anx7688 = devm_kzalloc(dev, sizeof(*anx7688), GFP_KERNEL);
> +	if (!anx7688)
> +		return -ENOMEM;
> +
> +#if IS_ENABLED(CONFIG_OF)
> +	anx7688->bridge.of_node = client->dev.of_node;
> +#endif
> +
> +	anx7688->client = client;
> +	i2c_set_clientdata(client, anx7688);
> +
> +	anx7688->regmap =
> +		devm_regmap_init_i2c(client, &anx7688_regmap_config);
> +
> +	/* Read both vendor and device id (4 bytes). */
> +	ret = regmap_bulk_read(anx7688->regmap, VENDOR_ID_REG, buffer, 4);
> +	if (ret) {
> +		dev_err(dev, "Failed to read chip vendor/device id\n");
> +		return ret;
> +	}
> +
> +	vendor = (u16)buffer[1] << 8 | buffer[0];
> +	device = (u16)buffer[3] << 8 | buffer[2];
> +	if (vendor != VENDOR_ID || device != DEVICE_ID) {
> +		dev_err(dev, "Invalid vendor/device id %04x/%04x\n",
> +			vendor, device);
> +		return -ENODEV;
> +	}
> +
> +	ret = regmap_bulk_read(anx7688->regmap, FW_VERSION_REG, buffer, 2);
> +	if (ret) {
> +		dev_err(&client->dev, "Failed to read firmware version\n");
> +		return ret;
> +	}
> +
> +	fwversion = (u16)buffer[0] << 8 | buffer[1];
> +	dev_info(dev, "ANX7688 firwmare version %02x.%02x\n",
> +		 buffer[0], buffer[1]);
> +
> +	/* FW version >= 0.85 supports bandwidth/lane count registers */
> +	if (fwversion >= MINIMUM_FW_VERSION) {
> +		anx7688->filter = true;
> +	} else {
> +		/* Warn, but not fail, for backwards compatibility. */
> +		dev_warn(dev,
> +			 "Old ANX7688 FW version (%02x.%02x), not filtering\n",
> +			 buffer[0], buffer[1]);
> +	}
> +
> +	anx7688->bridge.funcs = &anx7688_bridge_funcs;
> +	drm_bridge_add(&anx7688->bridge);
> +
> +	return 0;
> +}
> +
> +static int anx7688_i2c_remove(struct i2c_client *client)
> +{
> +	struct anx7688 *anx7688 = i2c_get_clientdata(client);
> +
> +	drm_bridge_remove(&anx7688->bridge);
> +
> +	return 0;
> +}
> +
> +static const struct i2c_device_id anx7688_id[] = {
> +	{ "anx7688", 0 },
> +	{ /* sentinel */ }
> +};
> +
> +MODULE_DEVICE_TABLE(i2c, anx7688_id);
> +
> +#if IS_ENABLED(CONFIG_OF)
> +static const struct of_device_id anx7688_match_table[] = {
> +	{ .compatible = "analogix,anx7688", },
> +	{ /* sentinel */ },
> +};
> +MODULE_DEVICE_TABLE(of, anx7688_match_table);
> +#endif
> +
> +static struct i2c_driver anx7688_driver = {
> +	.driver = {
> +		   .name = "anx7688",
> +		   .of_match_table = of_match_ptr(anx7688_match_table),
> +		  },
> +	.probe = anx7688_i2c_probe,
> +	.remove = anx7688_i2c_remove,
> +	.id_table = anx7688_id,
> +};
> +
> +module_i2c_driver(anx7688_driver);
> +
> +MODULE_DESCRIPTION("ANX7688 SlimPort Transmitter driver");
> +MODULE_AUTHOR("Nicolas Boichat <drinkcat@chromium.org>");
> +MODULE_LICENSE("GPL v2");

-- 
Regards,

Laurent Pinchart