Message-ID: <20150506121455.GB9421@ulmo>
Date:	Wed, 6 May 2015 14:14:56 +0200
From:	Thierry Reding <thierry.reding@...il.com>
To:	Shobhit Kumar <shobhit.kumar@...el.com>
Cc:	intel-gfx <intel-gfx@...ts.freedesktop.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-gpio <linux-gpio@...r.kernel.org>,
	linux-pwm <linux-pwm@...r.kernel.org>,
	dri-devel <dri-devel@...ts.freedesktop.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Alexandre Courbot <gnurou@...il.com>,
	Daniel Vetter <daniel.vetter@...el.com>,
	David Airlie <airlied@...ux.ie>,
	Samuel Ortiz <sameo@...ux.intel.com>,
	Jani Nikula <jani.nikula@...el.com>,
	Lee Jones <lee.jones@...aro.org>,
	Povilas Staniulis <wdmonster@...il.com>,
	Chih-Wei Huang <cwhuang@...roid-x86.org>
Subject: Re: [PATCH 6/8] pwm: crc: Add Crystalcove (CRC) PWM driver

On Tue, May 05, 2015 at 03:08:36PM +0530, Shobhit Kumar wrote:
> The Crystalcove PMIC controls PWM signals and this driver exports that

You say signal_s_ here, but you only expose a single PWM device. Does
the PMIC really control more than one? If it isn't, this should probably
become: "controls a PWM output and this driver...".

> capability as a PWM chip driver. This is platform device implementtaion

"implementation"

> of the drivers/mfd cell device for CRC PMIC

Sentences should end with a full stop.

> diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
> index b1541f4..954da3e 100644
> --- a/drivers/pwm/Kconfig
> +++ b/drivers/pwm/Kconfig
> @@ -183,6 +183,13 @@ config PWM_LPC32XX
>  	  To compile this driver as a module, choose M here: the module
>  	  will be called pwm-lpc32xx.
>  
> +config PWM_CRC
> +	bool "Intel Crystalcove (CRC) PWM support"
> +	depends on X86 && INTEL_SOC_PMIC
> +	help
> +	  Generic PWM framework driver for Crystalcove (CRC) PMIC based PWM
> +	  control.
> +

This is badly sorted. Please keep the list sorted alphabetically.

>  config PWM_LPSS
>  	tristate "Intel LPSS PWM support"
>  	depends on X86
> diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile
> index ec50eb5..3d38fed 100644
> --- a/drivers/pwm/Makefile
> +++ b/drivers/pwm/Makefile
> @@ -35,3 +35,4 @@ obj-$(CONFIG_PWM_TIPWMSS)	+= pwm-tipwmss.o
>  obj-$(CONFIG_PWM_TWL)		+= pwm-twl.o
>  obj-$(CONFIG_PWM_TWL_LED)	+= pwm-twl-led.o
>  obj-$(CONFIG_PWM_VT8500)	+= pwm-vt8500.o
> +obj-$(CONFIG_PWM_CRC)		+= pwm-crc.o

This too.

> diff --git a/drivers/pwm/pwm-crc.c b/drivers/pwm/pwm-crc.c
> new file mode 100644
> index 0000000..987f3b4
> --- /dev/null
> +++ b/drivers/pwm/pwm-crc.c
> @@ -0,0 +1,171 @@
> +/*
> + * pwm-crc.c - Intel Crystal Cove PWM Driver

I think you can safely remove this line. You already know what file it
is when you open it in your editor, and the description is in the
MODULE_DESCRIPTION string already.

> + *
> + * Copyright (C) 2015 Intel Corporation. All rights reserved.
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public License version
> + * 2 as published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + *
> + * Author: Shobhit Kumar <shobhit.kumar@...el.com>
> + */
> +
> +#include <linux/module.h>
> +#include <linux/platform_device.h>
> +#include <linux/regmap.h>
> +#include <linux/mfd/intel_soc_pmic.h>
> +#include <linux/pwm.h>
> +
> +#define PWM0_CLK_DIV		0x4B
> +#define  PWM_OUTPUT_ENABLE	(1<<7)

Should have spaces around <<.

> +#define  PWM_DIV_CLK_0		0x00 /* DIVIDECLK = BASECLK */
> +#define  PWM_DIV_CLK_100	0x63 /* DIVIDECLK = BASECLK/100 */
> +#define  PWM_DIV_CLK_128	0x7F /* DIVIDECLK = BASECLK/128 */
> +
> +#define PWM0_DUTY_CYCLE		0x4E
> +#define BACKLIGHT_EN		0x51
> +
> +#define PWM_MAX_LEVEL		0xFF
> +
> +#define PWM_BASE_CLK		6000	/* 6 MHz */

This number is actually 6 KHz. I think it'd be better if you stuck with
one unit here. Or perhaps there's some other reason why you can't use
6000000 here instead?

> +#define PWM_MAX_PERIOD_NS	21333 /* 46.875KHz */
> +
> +/**
> + * struct crystalcove_pwm - Crystal Cove PWM controller
> + * @chip: the abstract pwm_chip structure.
> + * @regmap: the regmap from the parent device.
> + */
> +struct crystalcove_pwm {
> +	struct pwm_chip chip;
> +	struct platform_device *pdev;

I think I had at some point requested that you get rid of this and use
the chip.dev member instead. There's no kerneldoc for it and it isn't
(well, almost, see below) used anywhere else, so perhaps you forgot to
remove it here?

> +	struct regmap *regmap;
> +};
> +
> +static inline struct crystalcove_pwm *to_crc_pwm(struct pwm_chip *pc)
> +{
> +	return container_of(pc, struct crystalcove_pwm, chip);
> +}
> +
> +static int crc_pwm_enable(struct pwm_chip *c, struct pwm_device *pwm)
> +{
> +	struct crystalcove_pwm *crc_pwm = to_crc_pwm(c);
> +
> +	regmap_write(crc_pwm->regmap, BACKLIGHT_EN, 1);
> +
> +	return 0;
> +}
> +
> +static void crc_pwm_disable(struct pwm_chip *c, struct pwm_device *pwm)
> +{
> +	struct crystalcove_pwm *crc_pwm = to_crc_pwm(c);
> +
> +	regmap_write(crc_pwm->regmap, BACKLIGHT_EN, 0);
> +}
> +
> +static int crc_pwm_config(struct pwm_chip *c, struct pwm_device *pwm,
> +				  int duty_ns, int period_ns)

Please align arguments on subsequent lines with the first argument of
the first line.

> +{
> +	struct crystalcove_pwm *crc_pwm = to_crc_pwm(c);
> +	struct device *dev = &crc_pwm->pdev->dev;

Did you test reconfiguring the PWM? I don't see crc_pwm->pdev getting
initialized anywhere, so this should crash trying to dereference a NULL
pointer.

Of course if you get rid of the pdev field as I suggested you can simply
get the struct device * from c->dev.

> +	int level, percent;
> +
> +	if (period_ns > PWM_MAX_PERIOD_NS) {
> +		dev_err(dev, "un-supported period_ns\n");
> +		return -1;

You should return -EINVAL here. Besides being a literal and therefore a
bad idea, -1 == -EPERM and doesn't match the error condition.

> +	}
> +
> +	if (pwm->period != period_ns) {
> +		int clk_div;
> +
> +		/* changing the clk divisor, need to disable fisrt */
> +		crc_pwm_disable(c, pwm);
> +		clk_div = PWM_BASE_CLK * period_ns / 1000000;

Similar to the above, this is confusing because you're mixing up
different scales here. period_ns is in nanoseconds, so it'd be natural
to divide by 1000000000 (though you should really be using NSEC_PER_SEC
instead). If you counterweight that by expressing PWM_BASE_CLK in Hz
(6000000) you get much nicer symmetry and make the code a lot easier to
understand.

> +
> +		regmap_write(crc_pwm->regmap, PWM0_CLK_DIV,
> +					clk_div | PWM_OUTPUT_ENABLE);
> +
> +		/* enable back */
> +		crc_pwm_enable(c, pwm);
> +	}
> +
> +	if (duty_ns > period_ns) {
> +		dev_err(dev, "duty cycle cannot be greater than cycle period\n");
> +		return -1;
> +	}

The PWM core already performs this check, so you'll never get here in
case this condition is true.

> +
> +	/* change the pwm duty cycle */
> +	percent = duty_ns * 100 / period_ns;
> +	level = percent * PWM_MAX_LEVEL / 100;

Why do you need to apply the rule of three twice here? Doesn't

	level = duty_ns * PWM_MAX_LEVEL / period_ns;

give you what you want?

> +	regmap_write(crc_pwm->regmap, PWM0_DUTY_CYCLE, level);
> +
> +	return 0;
> +}
> +
> +static const struct pwm_ops crc_pwm_ops = {
> +	.config = crc_pwm_config,
> +	.enable = crc_pwm_enable,
> +	.disable = crc_pwm_disable,
> +	.owner = THIS_MODULE,
> +};
> +
> +static int crystalcove_pwm_probe(struct platform_device *pdev)
> +{
> +	struct crystalcove_pwm *pwm;
> +	int retval;
> +	struct device *dev = pdev->dev.parent;
> +	struct intel_soc_pmic *pmic = dev_get_drvdata(dev);
> +
> +	pwm = devm_kzalloc(&pdev->dev, sizeof(*pwm), GFP_KERNEL);
> +	if (!pwm)
> +		return -ENOMEM;
> +
> +	pwm->chip.dev = &pdev->dev;
> +	pwm->chip.ops = &crc_pwm_ops;
> +	pwm->chip.base = -1;
> +	pwm->chip.npwm = 1;
> +
> +	/* get the PMIC regmap */
> +	pwm->regmap = pmic->regmap;
> +
> +	retval = pwmchip_add(&pwm->chip);
> +	if (retval < 0)
> +		return retval;
> +
> +	dev_dbg(&pdev->dev, "crc-pwm probe successful\n");

Do you really want this? The driver core will complain in any of the
above failures, so what use is there to be chatty when probing
succeeds?

> +static struct platform_driver crystalcove_pwm_driver = {
> +	.probe = crystalcove_pwm_probe,
> +	.remove = crystalcove_pwm_remove,
> +	.driver = {
> +		.name = "crystal_cove_pwm",

I'd prefer this to be "crystal-cove-pwm" for consistency with other
drivers, but since the MFD part already uses underscores in names it'd
introduce an inconsistency there. So I'm fine with this one as-is.

Thierry

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