Re: [Intel-gfx] [PATCH 6/8] pwm: crc: Add Crystalcove (CRC) PWM driver

[Shobhit Kumar <kumar@xxxxxxxxxxxx>]

On Wed, May 6, 2015 at 5:44 PM, Thierry Reding <thierry.reding@xxxxxxxxx> wrote:
> 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...".

Actually it does support 3 of them but on the platform only one is
being used and I exported only that as of now. Probably I should
expand a little in the commit message indicating this. will re-post
after fixing based on your other comments.

Regards
Shobhit

>
>> 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@xxxxxxxxx>
>> + */
>> +
>> +#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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>
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