Subject: [PATCH v4 1/4] pwm: add CSR SiRFSoC PWM driver

From: [email-masked] (Thierry Reding)
Date: Tue, 18 Mar 2014 22:03:17 +0100

On Wed, Mar 05, 2014 at 05:58:26PM +0800, Barry Song wrote:
> From: Huayi Li <[email-masked]>
> 
> PWM controller of CSR SiRFSoC can generate 7 independent outputs. Each output
> duty cycle can be adjusted by setting the corresponding wait & hold registers.
> There are 6 external channels (0 to 5) and 1 internal channel (6).
> Supports a wide frequency range: the source clock divider can be from 2
> up to 65536*2.

This commit message is too wide. Please always wrap the commit message
at 72 characters. See this for reference[0].

[0]: http://tbaggery.com/2008/04/19/a-note-about-git-commit-messages.html

> diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
[...]
> +config PWM_SIRF
> +	tristate "SiRF PWM support"
> +	depends on (ARCH_SIRF || COMPILE_TEST) && COMMON_CLK && OF

I'd prefer these to be split into more lines for readability, like so:

	depends on ARCH_SIRF || COMPILE_TEST
	depends on COMMON_CLK
	depends on OF

> diff --git a/drivers/pwm/pwm-sirf.c b/drivers/pwm/pwm-sirf.c
[...]
> + * Licensed under GPLv2.
> + */
> +#include <linux/kernel.h>

Could use a blank line between the above two, visually separating the
header comment from the list of include files.

> +#include <linux/init.h>
> +#include <linux/module.h>
> +#include <linux/device.h>
> +#include <linux/platform_device.h>
> +#include <linux/clk.h>
> +#include <linux/delay.h>
> +#include <linux/pwm.h>
> +#include <linux/of.h>
> +#include <linux/io.h>

Also please keep these sorted alphabetically.

> +struct sirf_pwm {
> +	struct pwm_chip	chip;

There's a tab between pwm_chip and chip here. It should be a space.

> +	struct mutex mutex;
> +	void __iomem *base;
> +	struct clk *pwmc_clk;
> +	/*  select OSC(26MHz) as clock source to generate PWM signals */
> +	struct clk *sigsrc_clk;

Maybe I'm missing something, but what in this driver is selecting the
OSC as clock source?

> +	unsigned long sigsrc_clk_rate;

Why do you cache this value? Can't you simply query the clock framework
for it when you need it?

> +static u32 sirf_pwm_ns_to_cycles(struct pwm_chip *chip, u32 time_ns)
> +{
> +	struct sirf_pwm *spwm = to_sirf_pwm_chip(chip);
> +	u64 dividend;
> +	u32 cycle;
> +
> +	dividend = (u64)spwm->sigsrc_clk_rate * time_ns + NSEC_PER_SEC / 2;
> +	do_div(dividend, NSEC_PER_SEC);
> +
> +	cycle = dividend;
> +
> +	return cycle > 1 ? cycle : 1;
> +}

I think you can do without the cycle variable here.

> +static int sirf_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
> +			int duty_ns, int period_ns)

Please always align the first argument on subsequent lines with the
first argument on the first line.

> +{
> +	u32 period_cycles, high_cycles, low_cycles;
> +	struct sirf_pwm *spwm = to_sirf_pwm_chip(chip);
> +
> +	/* use OSC to generate PWM signals */
> +	period_cycles = sirf_pwm_ns_to_cycles(chip, period_ns);

Again, how is this OSC specific?

> +	if (period_cycles == 1)
> +		return -EINVAL;
> +
> +	high_cycles = sirf_pwm_ns_to_cycles(chip, duty_ns);
> +	low_cycles = period_cycles - high_cycles;
> +
> +	mutex_lock(&spwm->mutex);
> +
> +	if (high_cycles == period_cycles) {
> +		high_cycles--;
> +		low_cycles = 1;
> +	}

This perhaps could use a comment. Why is it that the hardware can't be
programmed to high_cycles == period_cycles?

Also since you're only accessing local variables here you can safely
move this block out of the lock.

> +static int sirf_pwm_enable(struct pwm_chip *chip, struct pwm_device *pwm)
> +{
> +	struct sirf_pwm *spwm = to_sirf_pwm_chip(chip);
> +	u32 val;
> +
> +	mutex_lock(&spwm->mutex);
> +
> +	/* disable preclock */
> +	val = readl(spwm->base + SIRF_PWM_ENABLE_PRECLOCK);
> +	val &= ~(1 << pwm->hwpwm);
> +	writel(val, spwm->base + SIRF_PWM_ENABLE_PRECLOCK);
> +
> +	/* select preclock source must after disable preclk*/

Missing space between "preclk" and "*/".

> +	val = readl(spwm->base + SIRF_PWM_SELECT_PRECLK);
> +	val &= ~(0x1 << (BYPASS_MODE_BIT + pwm->hwpwm));
> +	val &= ~(0x7 << (SRC_FIELD_SIZE * pwm->hwpwm));

Perhaps the source field is used to configure which clock is used? In
that case I suggest you reshuffle the comments a bit. For example I
think it would be clearer if you stated in the file's header comment
that the driver currently only works if the OSC is used as the signal
source clock and make a comment here that this selects OSC.

One thing that worries me slightly is that there's no way we can
determine from a struct clk what clock it actually is. So it's
impossible to derive from a struct clk that it is indeed the OSC and
therefore this driver has no means to be extensible in the future.

But I have no idea how to solve this properly. Perhaps this would
somehow need to be modeled within the clock framework?

> +static int sirf_pwm_probe(struct platform_device *pdev)
> +{
> +	struct sirf_pwm *spwm;
> +	struct resource *mem_res;
> +	int ret;
> +
> +	spwm = devm_kzalloc(&pdev->dev, sizeof(*spwm), GFP_KERNEL);
> +	if (!spwm)
> +		return -ENOMEM;
> +
> +	platform_set_drvdata(pdev, spwm);
> +
> +	mem_res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> +	spwm->base = devm_ioremap_resource(&pdev->dev, mem_res);
> +	if (!spwm->base)
> +		return -ENOMEM;

devm_ioremap_resource() returns an ERR_PTR() encoded error on failure,
so the proper way to check for this is:

	if (IS_ERR(spwm->base))
		return PTR_ERR(spwm->base);

> +	/*
> +	 * clock for PWM controller
> +	 */
> +	spwm->pwmc_clk = devm_clk_get(&pdev->dev, "pwmc");

I think you could drop the pwmc_ prefix, but I don't feel too strongly
about that.

> +	if (IS_ERR(spwm->pwmc_clk)) {
> +		dev_err(&pdev->dev, "failed to get PWM controller clock\n");
> +		return PTR_ERR(spwm->pwmc_clk);
> +	}
> +
> +	ret = clk_prepare_enable(spwm->pwmc_clk);
> +	if (ret)
> +		return ret;
> +
> +	/*
> +	 * clocks to generate PWM signals, we use OSC with 26MHz
> +	 */

Only a single clock is requested here, so "clock to generate...". And
again there's a reference to OSC and 26 MHz here, but the code is
completely generic and it could in fact be any other clock.

> +	spwm->sigsrc_clk = devm_clk_get(&pdev->dev, "sigsrc0");
> +	if (IS_ERR(spwm->sigsrc_clk)) {
> +		dev_err(&pdev->dev, "failed to get PWM signal source clock0\n");
> +		ret = PTR_ERR(spwm->sigsrc_clk);
> +		goto err_src_clk;
> +	}

Why is this called "sigsrc0" if there's only one?

> +	spwm->sigsrc_clk_rate = clk_get_rate(spwm->sigsrc_clk);

I guess this could be no issue at all if sigsrc_clk indeed always is
OSC, but caching the rate of the source clock is bad because it gives
you no chance at all to adapt to clock rate changes later on (if that
even happens). So in order not to set a bad example, I'd rather see this
not cached, but queried when needed.

> +	spwm->chip.dev = &pdev->dev;
> +	spwm->chip.ops = &sirf_pwm_ops;
> +	spwm->chip.base = 0;

I think you should want to set this to -1.

> +		dev_err(&pdev->dev, "failed to register PWM\n");

"PWM chip", please.

> +static int sirf_pwm_remove(struct platform_device *pdev)
> +{
> +	struct sirf_pwm *spwm = platform_get_drvdata(pdev);
> +
> +	clk_disable_unprepare(spwm->pwmc_clk);
> +	clk_disable_unprepare(spwm->sigsrc_clk);
> +
> +	return pwmchip_remove(&spwm->chip);
> +}

Don't you want to remove the chip first, before disabling all the
clocks? pwmchip_remove() may end up accessing registers that need the
clock enabled.

> +static int sirf_pwm_suspend(struct device *dev)
> +{
> +	struct platform_device *pdev = to_platform_device(dev);
> +	struct sirf_pwm *spwm = platform_get_drvdata(pdev);
> +
> +	clk_disable_unprepare(spwm->pwmc_clk);
> +
> +	return 0;
> +}

Why doesn't this disable (and unprepare) the source clock?

> +static void sirf_pwm_config_restore(struct sirf_pwm *spwm)
> +{
> +	struct pwm_device *pwm;
> +	int i;
> +
> +	for (i = 0; i < spwm->chip.npwm; i++) {
> +		pwm = &spwm->chip.pwms[i];
> +		/*
> +		 * while restoring from hibernation, state of pwm is enabled,

pwm -> PWM, please.

> +static int sirf_pwm_restore(struct device *dev)
> +{
> +	struct sirf_pwm *spwm = dev_get_drvdata(dev);
> +
> +	/* back from hibernation, clock is already enabled */
> +	sirf_pwm_config_restore(spwm);
> +
> +	return 0;
> +}
> +
> +#else

Gratuitous blank line above this one.

> +static struct platform_driver sirf_pwm_driver = {
> +	.driver = {
> +		.name = "sirf-pwm",
> +		.pm = &sirf_pwm_pm_ops,
> +		.of_match_table = sirf_pwm_of_match,
> +	},
> +	.probe = sirf_pwm_probe,
> +	.remove = sirf_pwm_remove,
> +};
> +
> +module_platform_driver(sirf_pwm_driver);

Another gratuitous blank line above this one.

Thierry
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