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Date:   Thu, 9 May 2019 09:20:18 +0200
From:   Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= 
        <u.kleine-koenig@pengutronix.de>
To:     Anson Huang <anson.huang@nxp.com>
Cc:     "thierry.reding@gmail.com" <thierry.reding@gmail.com>,
        "robh+dt@kernel.org" <robh+dt@kernel.org>,
        "mark.rutland@arm.com" <mark.rutland@arm.com>,
        "shawnguo@kernel.org" <shawnguo@kernel.org>,
        "s.hauer@pengutronix.de" <s.hauer@pengutronix.de>,
        "kernel@pengutronix.de" <kernel@pengutronix.de>,
        "festevam@gmail.com" <festevam@gmail.com>,
        "linux@armlinux.org.uk" <linux@armlinux.org.uk>,
        "stefan@agner.ch" <stefan@agner.ch>,
        "otavio@ossystems.com.br" <otavio@ossystems.com.br>,
        Leonard Crestez <leonard.crestez@nxp.com>,
        Robin Gong <yibin.gong@nxp.com>,
        "linux-pwm@vger.kernel.org" <linux-pwm@vger.kernel.org>,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        dl-linux-imx <linux-imx@nxp.com>
Subject: Re: [PATCH V11 2/5] pwm: Add i.MX TPM PWM driver support
Message-ID: <20190509072018.cenumkgbysfba57l@pengutronix.de>
References: <1554860547-18237-1-git-send-email-Anson.Huang@nxp.com>
 <1554860547-18237-3-git-send-email-Anson.Huang@nxp.com>
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Hello,

On Wed, Apr 10, 2019 at 01:47:40AM +0000, Anson Huang wrote:
> i.MX7ULP has TPM(Low Power Timer/Pulse Width Modulation Module)
> inside, it can support multiple PWM channels, all the channels
> share same counter and period setting, but each channel can
> configure its duty and polarity independently.
> 
> There are several TPM modules in i.MX7ULP, the number of channels
> in TPM modules are different, it can be read from each TPM module's
> PARAM register.
> 
> Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
> ---
> Changes since V10:
> 	- remove channel private data which is ONLY for storing polarity, just read it from HW register;
> 	- improve pwm_imx_tpm_round_state() and pwm_imx_tpm_apply_hw() parameters sequence;
> 	- improve comments for polarity setting;
> 	- refuse polarity change if PWM is active.
> ---
>  drivers/pwm/Kconfig       |  11 ++
>  drivers/pwm/Makefile      |   1 +
>  drivers/pwm/pwm-imx-tpm.c | 442 ++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 454 insertions(+)
>  create mode 100644 drivers/pwm/pwm-imx-tpm.c
> 
> diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
> index c054bd1..1311b540 100644
> --- a/drivers/pwm/Kconfig
> +++ b/drivers/pwm/Kconfig
> @@ -210,6 +210,17 @@ config PWM_IMX27
>  	  To compile this driver as a module, choose M here: the module
>  	  will be called pwm-imx27.
>  
> +config PWM_IMX_TPM
> +	tristate "i.MX TPM PWM support"
> +	depends on ARCH_MXC || COMPILE_TEST
> +	depends on HAVE_CLK && HAS_IOMEM
> +	help
> +	  Generic PWM framework driver for i.MX7ULP TPM module, TPM's full
> +	  name is Low Power Timer/Pulse Width Modulation Module.
> +
> +	  To compile this driver as a module, choose M here: the module
> +	  will be called pwm-imx-tpm.
> +
>  config PWM_JZ4740
>  	tristate "Ingenic JZ47xx PWM support"
>  	depends on MACH_INGENIC
> diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile
> index 448825e..c368599 100644
> --- a/drivers/pwm/Makefile
> +++ b/drivers/pwm/Makefile
> @@ -19,6 +19,7 @@ obj-$(CONFIG_PWM_HIBVT)		+= pwm-hibvt.o
>  obj-$(CONFIG_PWM_IMG)		+= pwm-img.o
>  obj-$(CONFIG_PWM_IMX1)		+= pwm-imx1.o
>  obj-$(CONFIG_PWM_IMX27)		+= pwm-imx27.o
> +obj-$(CONFIG_PWM_IMX_TPM)	+= pwm-imx-tpm.o
>  obj-$(CONFIG_PWM_JZ4740)	+= pwm-jz4740.o
>  obj-$(CONFIG_PWM_LP3943)	+= pwm-lp3943.o
>  obj-$(CONFIG_PWM_LPC18XX_SCT)	+= pwm-lpc18xx-sct.o
> diff --git a/drivers/pwm/pwm-imx-tpm.c b/drivers/pwm/pwm-imx-tpm.c
> new file mode 100644
> index 0000000..9349f4f
> --- /dev/null
> +++ b/drivers/pwm/pwm-imx-tpm.c
> @@ -0,0 +1,442 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright 2018-2019 NXP.
> + *
> + * Limitations:
> + * - The TPM counter and period counter are shared between
> + *   multiple channels, so all channels should use same period
> + *   settings.
> + * - Changes to polarity cannot be latched at the time of the
> + *   next period start.
> + * - Changing period and duty cycle together isn't atomic,
> + *   with the wrong timing it might happen that a period is
> + *   produced with old duty cycle but new period settings.
> + */
> +
> +#include <linux/bitfield.h>
> +#include <linux/bitops.h>
> +#include <linux/clk.h>
> +#include <linux/err.h>
> +#include <linux/io.h>
> +#include <linux/log2.h>
> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/of_address.h>
> +#include <linux/platform_device.h>
> +#include <linux/pwm.h>
> +#include <linux/slab.h>
> +
> +#define PWM_IMX_TPM_PARAM	0x4
> +#define PWM_IMX_TPM_GLOBAL	0x8
> +#define PWM_IMX_TPM_SC		0x10
> +#define PWM_IMX_TPM_CNT		0x14
> +#define PWM_IMX_TPM_MOD		0x18
> +#define PWM_IMX_TPM_CnSC(n)	(0x20 + (n) * 0x8)
> +#define PWM_IMX_TPM_CnV(n)	(0x24 + (n) * 0x8)
> +
> +#define PWM_IMX_TPM_PARAM_CHAN			GENMASK(7, 0)
> +
> +#define PWM_IMX_TPM_SC_PS			GENMASK(2, 0)
> +#define PWM_IMX_TPM_SC_CMOD			GENMASK(4, 3)
> +#define PWM_IMX_TPM_SC_CMOD_INC_EVERY_CLK	FIELD_PREP(PWM_IMX_TPM_SC_CMOD, 1)
> +#define PWM_IMX_TPM_SC_CPWMS			BIT(5)
> +
> +#define PWM_IMX_TPM_CnSC_CHF	BIT(7)
> +#define PWM_IMX_TPM_CnSC_MSB	BIT(5)
> +#define PWM_IMX_TPM_CnSC_MSA	BIT(4)
> +
> +/*
> + * The reference manual describes this field as two separate bits. The
> + * semantic of the two bits isn't orthogonal though, so they are treated
> + * together as a 2-bit field here.
> + */
> +#define PWM_IMX_TPM_CnSC_ELS	GENMASK(3, 2)
> +#define PWM_IMX_TPM_CnSC_ELS_INVERSED	FIELD_PREP(PWM_IMX_TPM_CnSC_ELS, 1)
> +#define PWM_IMX_TPM_CnSC_ELS_NORMAL	FIELD_PREP(PWM_IMX_TPM_CnSC_ELS, 2)
> +
> +
> +#define PWM_IMX_TPM_MOD_WIDTH	16
> +#define PWM_IMX_TPM_MOD_MOD	GENMASK(PWM_IMX_TPM_MOD_WIDTH - 1, 0)
> +
> +struct imx_tpm_pwm_chip {
> +	struct pwm_chip chip;
> +	struct clk *clk;
> +	void __iomem *base;
> +	struct mutex lock;
> +	u32 user_count;
> +	u32 enable_count;
> +	u32 real_period;
> +};
> +
> +struct imx_tpm_pwm_param {
> +	u8 prescale;
> +	u32 mod;
> +	u32 val;
> +};
> +
> +static inline struct imx_tpm_pwm_chip *to_imx_tpm_pwm_chip(struct pwm_chip *chip)
> +{
> +	return container_of(chip, struct imx_tpm_pwm_chip, chip);
> +}
> +

Maybe add a comment here describing the purpose of this function.
Something like:

/* 
 * This function determines for a given pwm_state *state that a consumer
 * might request the pwm_state *realstate that eventually is implemented
 * by the hardware and the necessary register values (in *p) to achive
 * this.
 */

I didn't revalidate all the maths in this driver but assume they are
still right from the previous rounds. If you add the comment I suggested
above, feel free to also add

	Reviewed-by: Uwe Kleine-K?nig <u.kleine-koenig@pengutronix.de>

> +static int pwm_imx_tpm_round_state(struct pwm_chip *chip,
> +				   struct imx_tpm_pwm_param *p,
> +				   struct pwm_state *real_state,
> +				   struct pwm_state *state)
> +{
> +	struct imx_tpm_pwm_chip *tpm = to_imx_tpm_pwm_chip(chip);
> +	u32 rate, prescale, period_count, clock_unit;
> +	u64 tmp;
> +
> +	rate = clk_get_rate(tpm->clk);
> +	tmp = (u64)state->period * rate;
> +	clock_unit = DIV_ROUND_CLOSEST_ULL(tmp, NSEC_PER_SEC);
> +	if (clock_unit <= PWM_IMX_TPM_MOD_MOD)
> +		prescale = 0;
> +	else
> +		prescale = ilog2(clock_unit) + 1 - PWM_IMX_TPM_MOD_WIDTH;
> +
> +	if ((!FIELD_FIT(PWM_IMX_TPM_SC_PS, prescale)))
> +		return -ERANGE;

It's a bit sad that my ideas for the core concerning a round_rate
callback don't go down particularly well on Thierry's side. 

With the way I suggested we'd continue with prescale = 7 in this case.

As of now there is no rule which kind of deviation to accept and which
not. :-| (Nothing this patch can change of course.)

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-K?nig            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |