Re: [PATCH] pwm: add spear pwm driver support

[Shiraz Hashim <shiraz.hashim@st.com>]

Hi Thierry,

Thanks for the quick review.

On Thu, Oct 18, 2012 at 02:08:20PM +0200, Thierry Reding wrote:
> On Thu, Oct 18, 2012 at 04:58:32PM +0530, Shiraz Hashim wrote:
> > Add support for pwm devices present on SPEAr platforms.  These pwm
> > devices support 4 channel output with programmable duty cycle and
> > frequency.
> > 
> > More details on these pwm devices can be obtained from relevant chapter
> > of reference manual, present at following[1] location.
> 
> Please make sure to spell PWM consistently. It should be in all
> uppercase in text. Lowercase should only be used in variable names or
> the patch subject prefix. See other commit messages for examples. The
> same applies to the rest of this patch, which seems to use a random mix
> of both.
> 
> And maybe this shouldn't say "Add support for pwm devices" but rather
> "Add support for PWM chips..." and "These PWM chips support..."

I would do that.

> > 
> > 1. http://www.st.com/internet/mcu/product/251211.jsp
> > 
> > Cc: Thierry Reding <thierry.reding@avionic-design.de>
> > Signed-off-by: Shiraz Hashim <shiraz.hashim@st.com>
> > Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
> > Reviewed-by: Vipin Kumar <vipin.kumar@st.com>
> > ---
> >  .../devicetree/bindings/pwm/st-spear-pwm.txt       |   19 ++
> >  drivers/pwm/Kconfig                                |   10 +
> >  drivers/pwm/Makefile                               |    1 +
> >  drivers/pwm/pwm-spear.c                            |  287 ++++++++++++++++++++
> >  4 files changed, 317 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/pwm/st-spear-pwm.txt
> >  create mode 100644 drivers/pwm/pwm-spear.c
> > 
> > diff --git a/Documentation/devicetree/bindings/pwm/st-spear-pwm.txt b/Documentation/devicetree/bindings/pwm/st-spear-pwm.txt
> > new file mode 100644
> > index 0000000..b3dd1a0
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/pwm/st-spear-pwm.txt
> 
> I think this should either be "spear-pwm.txt" to mirror the driver name,
> or, to follow the Tegra example, "st,spear-pwm.txt" to mirror the
> compatible property.

Okay. I would rename it to 'st,spear-pwm.txt'.

> > @@ -0,0 +1,19 @@
> > +== ST SPEAr SoC PWM controller ==
> > +
> > +Required properties:
> > +- compatible: should be one of:
> > +  - "st,spear-pwm"
> > +  - "st,spear13xx-pwm"
> > +- reg: physical base address and length of the controller's registers
> > +- #pwm-cells: number of cells used to specify PWM which is fixed to 2 on SPEAr. The
> 
> I think you can break the "The" to the next line to make it fit within
> the 80 character limit.

Sure.

> > +  first cell specifies the per-chip index of the PWM to use and the second
> > +  cell is the duty cycle in nanoseconds.
> 
> This should be "period in nanoseconds". I know this is wrong in the
> binding documentation for other drivers but I've recently committed a
> patch that fixes it.

Okay but I couldn't see use of pwm->period set by of_pwm_simple_xlate
anywhere. Am I missing something ?

> 
> > +
> > +Example:
> > +
> > +        pwm: pwm@a8000000 {
> > +            compatible ="st,spear-pwm";
> > +            reg = <0xa8000000 0x1000>;
> > +            #pwm-cells = <2>;
> > +            status = "disabled";
> > +        };
> > diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
> > index ed81720..3ff3e6f 100644
> > --- a/drivers/pwm/Kconfig
> > +++ b/drivers/pwm/Kconfig
> > @@ -112,6 +112,16 @@ config PWM_SAMSUNG
> >  	  To compile this driver as a module, choose M here: the module
> >  	  will be called pwm-samsung.
> >  
> > +config PWM_SPEAR
> > +	tristate "STMicroelectronics SPEAR PWM support"
> 
> You've spelled this "SPEAr" above and below, why not keep that spelling
> here as well?
> 

Thanks for pointing out, would fix it.

> > +	depends on PLAT_SPEAR
> > +	help
> > +	  Generic PWM framework driver for the PWM controller on ST
> > +	  SPEAr SoCs.
> > +
> > +	  To compile this driver as a module, choose M here: the module
> > +	  will be called pwm-spear.
> > +
> >  config PWM_TEGRA
> >  	tristate "NVIDIA Tegra PWM support"
> >  	depends on ARCH_TEGRA
> > diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile
> > index acfe482..6512786 100644
> > --- a/drivers/pwm/Makefile
> > +++ b/drivers/pwm/Makefile
> > @@ -9,6 +9,7 @@ obj-$(CONFIG_PWM_PUV3)		+= pwm-puv3.o
> >  obj-$(CONFIG_PWM_PXA)		+= pwm-pxa.o
> >  obj-$(CONFIG_PWM_SAMSUNG)	+= pwm-samsung.o
> >  obj-$(CONFIG_PWM_TEGRA)		+= pwm-tegra.o
> > +obj-$(CONFIG_PWM_SPEAR)		+= pwm-spear.o
> >  obj-$(CONFIG_PWM_TIECAP)	+= pwm-tiecap.o
> >  obj-$(CONFIG_PWM_TIEHRPWM)	+= pwm-tiehrpwm.o
> >  obj-$(CONFIG_PWM_TWL6030)	+= pwm-twl6030.o
> > diff --git a/drivers/pwm/pwm-spear.c b/drivers/pwm/pwm-spear.c
> > new file mode 100644
> > index 0000000..814395b
> > --- /dev/null
> > +++ b/drivers/pwm/pwm-spear.c
> > @@ -0,0 +1,287 @@
> > +/*
> > + * ST Microelectronics SPEAr Pulse Width Modulator driver
> > + *
> > + * Copyright (C) 2012 ST Microelectronics
> > + * Shiraz Hashim <shiraz.hashim@st.com>
> > + *
> > + * This file is licensed under the terms of the GNU General Public
> > + * License version 2. This program is licensed "as is" without any
> > + * warranty of any kind, whether express or implied.
> > + */
> > +
> > +#include <linux/clk.h>
> > +#include <linux/err.h>
> > +#include <linux/io.h>
> > +#include <linux/ioport.h>
> > +#include <linux/kernel.h>
> > +#include <linux/math64.h>
> > +#include <linux/module.h>
> > +#include <linux/of.h>
> > +#include <linux/platform_device.h>
> > +#include <linux/pwm.h>
> > +#include <linux/slab.h>
> > +
> > +/* PWM registers and bits definitions */
> > +#define PWMCR			0x00	/* Control Register */
> > +#define PWMDCR			0x04	/* Duty Cycle Register */
> > +#define PWMPCR			0x08	/* Period Register */
> > +/* Following only available on 13xx SoCs */
> > +#define PWMMCR			0x3C	/* Master Control Register */
> > +
> > +#define PWM_ENABLE		0x1
> > +
> > +#define MIN_PRESCALE		0x00
> > +#define MAX_PRESCALE		0x3FFF
> > +#define PRESCALE_SHIFT		2
> > +
> > +#define MIN_DUTY		0x0001
> > +#define MAX_DUTY		0xFFFF
> > +
> > +#define MIN_PERIOD		0x0001
> > +#define MAX_PERIOD		0xFFFF
> 
> Would it make sense to perhaps group the bitfields with the matching
> register definitions to make their use more obvious. Also I prefer
> lowercase hexadecimal digits, but that's pure bikeshedding.
> 

Sure I would group them, but uppercase hexadecimal digits clearly
seperate the value (number) which otherwise can be mixed (while
reading) with normal letters. Isn't it ?

> > +
> > +#define NUM_PWM			4
> > +
> > +/**
> > + * struct pwm: struct representing pwm ip
> > + *
> > + * mmio_base: base address of pwm
> > + * clk: pointer to clk structure of pwm ip
> > + * chip: linux pwm chip representation
> > + * dev: pointer to device structure of pwm
> > + */
> 
> This is not proper kerneldoc. Also the structure is called
> spear_pwm_chip below, while the comment says "struct pwm".

Stupid of me, would fix it.

> > +struct spear_pwm_chip {
> > +	void __iomem *mmio_base;
> > +	struct clk *clk;
> > +	struct pwm_chip	chip;
> > +	struct device *dev;
> > +};
> > +
> > +static inline struct spear_pwm_chip *to_spear_pwm_chip(struct pwm_chip *chip)
> > +{
> > +	return container_of(chip, struct spear_pwm_chip, chip);
> > +}
> > +
> > +static inline u32 spear_pwm_readl(struct spear_pwm_chip *chip, unsigned int num,
> > +		unsigned long offset)
> 
> I personally like it better to have function arguments aligned, like so:
> 
> static inline u32 spear_pwm_readl(struct spear_pwm_chip *chip, unsigned int num,
> 				  unsigned long offset)
> 
> Note, those are as many 8-spaces tabs with only spaces to align them
> properly. But again, pure bikeshedding and I won't force the issue.
> 

Would do that. Are you aware of some (vim) configuration which can
autmatically do this while editing code ?

> > +{
> > +	return readl_relaxed(chip->mmio_base + (num << 4) + offset);
> > +}
> > +
> > +static inline void spear_pwm_writel(struct spear_pwm_chip *chip,
> > +		unsigned int num, unsigned long offset, unsigned long val)
> > +{
> > +	writel_relaxed(val, chip->mmio_base + (num << 4) + offset);
> > +}
> > +
> > +/*
> > + * period_ns = 10^9 * (PRESCALE + 1) * PV / PWM_CLK_RATE
> > + * duty_ns = 10^9 * (PRESCALE + 1) * DC / PWM_CLK_RATE
> > + *
> > + * PV = (PWM_CLK_RATE * period_ns)/ (10^9 * (PRESCALE + 1))
> > + * DC = (PWM_CLK_RATE * duty_ns)/ (10^9 * (PRESCALE + 1))
> > + */
> > +int spear_pwm_config(struct pwm_chip *pwm, struct pwm_device *pwmd, int duty_ns,
> 
> If you call the pwm variable chip, there's no need to introduce the
> somewhat confusing pwmd. The same goes for the other callbacks below.
> 

I would rename pwm_chip instance as chip and pwm_device as pwm
everywhere.

> > +		int period_ns)
> > +{
> > +	struct spear_pwm_chip *pc = to_spear_pwm_chip(pwm);
> > +	u64 val, div, clk_rate;
> > +	unsigned long prescale = MIN_PRESCALE, pv, dc;
> > +	int ret = -EINVAL;
> > +
> > +	if (period_ns == 0 || duty_ns > period_ns)
> > +		goto err;
> 
> No need to check for these cases, they are already handled by the core.
> 

Okay, shall remove them.

> > +
> > +	/*
> > +	 * Find pv, dc and prescale to suit duty_ns and period_ns. This is done
> > +	 * according to formulas provided above this routine.
> > +	 */
> 
> Maybe you should move the formulas into this comment. That puts them
> more closely to where they are referred to.
> 

Fine.

> > +	clk_rate = clk_get_rate(pc->clk);
> > +	while (1) {
> > +		div = 1000000000;
> > +		div *= 1 + prescale;
> > +		val = clk_rate * period_ns;
> > +		pv = div64_u64(val, div);
> > +		val = clk_rate * duty_ns;
> > +		dc = div64_u64(val, div);
> > +
> > +		/* if duty_ns and period_ns are not acheivable then return */
> 
> "achievable"
> 

Would fix it and run a spell checker.

> > +		if (!pv || !dc || pv < MIN_PERIOD || dc < MIN_DUTY)
> > +			goto err;
> > +
> > +		/*
> > +		 * if pv and dc have crossed their upper limit, then increase
> > +		 * prescale and recalculate pv and dc.
> > +		 */
> > +		if ((pv > MAX_PERIOD) || (dc > MAX_DUTY)) {
> 
> The inner parentheses are not required.
> 

Fine.

> > +			prescale++;
> > +			if (prescale > MAX_PRESCALE)
> 
> Maybe condense into "if (++prescale > MAX_PRESCALE)"?
> 

Okay.

> > +				goto err;
> > +			continue;
> > +		}
> > +		break;
> > +	}
> > +
> > +	/*
> > +	 * NOTE: the clock to PWM has to be enabled first before writing to the
> > +	 * registers.
> > +	 */
> > +	ret = clk_prepare_enable(pc->clk);
> > +	if (ret)
> > +		goto err;
> > +
> > +	spear_pwm_writel(pc, pwmd->hwpwm, PWMCR, prescale << PRESCALE_SHIFT);
> > +	spear_pwm_writel(pc, pwmd->hwpwm, PWMDCR, dc);
> > +	spear_pwm_writel(pc, pwmd->hwpwm, PWMPCR, pv);
> > +	clk_disable_unprepare(pc->clk);
> > +
> > +	return 0;
> > +err:
> > +	dev_err(pc->dev, "pwm config fail\n");
> 
> You might want to output an error code here. But I don't think it is
> even necessary. Users of the PWM API are supposed to handle errors from
> pwm_config() properly, so this will in most cases just output a
> duplicate error message. Also, if you get rid of the message you can do
> away with the gotos and the label as well.

Right, I would remove it.

> 
> > +	return ret;
> > +}
> > +
> > +static int spear_pwm_enable(struct pwm_chip *pwm, struct pwm_device *pwmd)
> > +{
> > +	struct spear_pwm_chip *pc = to_spear_pwm_chip(pwm);
> > +	int rc = 0;
> > +	u32 val;
> > +
> > +	rc = clk_prepare_enable(pc->clk);
> > +	if (rc < 0)
> > +		return rc;
> > +
> > +	val = spear_pwm_readl(pc, pwmd->hwpwm, PWMCR);
> > +	val |= PWM_ENABLE;
> > +	spear_pwm_writel(pc, pwmd->hwpwm, PWMCR, val);
> > +
> > +	return 0;
> > +}
> > +
> > +static void spear_pwm_disable(struct pwm_chip *pwm, struct pwm_device *pwmd)
> > +{
> > +	struct spear_pwm_chip *pc = to_spear_pwm_chip(pwm);
> > +	u32 val;
> > +
> > +	val = spear_pwm_readl(pc, pwmd->hwpwm, PWMCR);
> > +	val &= ~PWM_ENABLE;
> > +	spear_pwm_writel(pc, pwmd->hwpwm, PWMCR, val);
> > +
> > +	clk_disable_unprepare(pc->clk);
> > +}
> > +
> > +static const struct pwm_ops spear_pwm_ops = {
> > +	.config = spear_pwm_config,
> > +	.enable = spear_pwm_enable,
> > +	.disable = spear_pwm_disable,
> > +	.owner = THIS_MODULE,
> > +};
> > +
> > +static int __devinit spear_pwm_probe(struct platform_device *pdev)
> 
> __devinit will go away sometime soon, so please don't use it in new
> code.
> 

Okay. You mean all init sections would eventually be removed. I
would read more about it.

> > +{
> > +	struct device_node *np = pdev->dev.of_node;
> > +	struct spear_pwm_chip *pc;
> > +	struct resource *r;
> > +	int ret;
> > +	u32 val;
> > +
> > +	pc = devm_kzalloc(&pdev->dev, sizeof(*pc), GFP_KERNEL);
> > +	if (!pc) {
> > +		dev_err(&pdev->dev, "failed to allocate memory\n");
> > +		return -ENOMEM;
> > +	}
> > +
> > +	pc->dev = &pdev->dev;
> > +
> > +	r = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> > +	if (!r) {
> > +		dev_err(&pdev->dev, "no memory resources defined\n");
> > +		return -ENODEV;
> > +	}
> > +
> > +	pc->mmio_base = devm_request_and_ioremap(&pdev->dev, r);
> > +	if (!pc->mmio_base)
> > +		return -EADDRNOTAVAIL;
> > +
> > +	platform_set_drvdata(pdev, pc);
> > +
> > +	pc->clk = devm_clk_get(&pdev->dev, NULL);
> > +	if (IS_ERR(pc->clk))
> > +		return PTR_ERR(pc->clk);
> > +
> > +	pc->chip.dev = &pdev->dev;
> > +	pc->chip.ops = &spear_pwm_ops;
> > +	pc->chip.base = -1;
> > +	pc->chip.npwm = NUM_PWM;
> > +
> > +	ret = pwmchip_add(&pc->chip);
> > +	if (ret < 0) {
> > +		dev_err(&pdev->dev, "pwmchip_add() failed: %d\n", ret);
> > +		return ret;
> > +	}
> > +
> > +	if (np && of_device_is_compatible(np, "st,spear13xx-pwm")) {
> > +		ret = clk_prepare_enable(pc->clk);
> > +		if (ret < 0)
> > +			return pwmchip_remove(&pc->chip);
> > +
> > +		/* Following enables PWM device, channels would still be
> > +		 * enabled individually through their control register
> > +		 **/
> 
> This is not a proper multi-line comment.
> 

:(, checkpatch didn't take notice here.

> > +		val = readl(pc->mmio_base + PWMMCR);
> > +		val |= PWM_ENABLE;
> > +		writel(val, pc->mmio_base + PWMMCR);
> > +
> > +		clk_disable_unprepare(pc->clk);
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> > +static int __devexit spear_pwm_remove(struct platform_device *pdev)
> 
> __devexit can be dropped as well.
> 

Sure.

> > +{
> > +	struct spear_pwm_chip *pc = platform_get_drvdata(pdev);
> > +	int i;
> > +
> > +	if (WARN_ON(!pc))
> > +		return -ENODEV;
> > +
> > +	for (i = 0; i < NUM_PWM; i++) {
> > +		struct pwm_device *pwmd = &pc->chip.pwms[i];
> 
> Again, the canonical name for this would be just plain "pwm".
> 

Okay.

> > +
> > +		if (!test_bit(PWMF_ENABLED, &pwmd->flags))
> > +			if (clk_prepare_enable(pc->clk) < 0)
> > +				continue;
> > +
> > +		spear_pwm_writel(pc, i, PWMCR, 0);
> > +		clk_disable_unprepare(pc->clk);
> > +	}
> > +
> > +	return pwmchip_remove(&pc->chip);
> > +}
> > +
> > +#ifdef CONFIG_OF
> > +static struct of_device_id spear_pwm_of_match[] = {
> > +	{ .compatible = "st,spear-pwm" },
> > +	{ .compatible = "st,spear13xx-pwm" },
> > +	{ }
> > +};
> > +
> > +MODULE_DEVICE_TABLE(of, spear_pwm_of_match);
> > +#endif
> 
> Is there a reason to make this conditional? It looks like SPEAr has
> moved to OF, so this will always be enabled anyway, won't it?

Yes, I would remove it, SPEAr cannot boot without DT.

> > +
> > +static struct platform_driver spear_pwm_driver = {
> > +	.driver = {
> > +		.name = "spear-pwm",
> > +		.of_match_table = of_match_ptr(spear_pwm_of_match),
> 
> Same here. If SPEAr is always OF, then of_match_ptr is useless.
> 

Sure.

> > +	},
> > +	.probe = spear_pwm_probe,
> > +	.remove = __devexit_p(spear_pwm_remove),
> 
> __devexit_p is also superfluous.
> 

Would remove this.

> > +};
> > +
> > +module_platform_driver(spear_pwm_driver);
> > +
> > +MODULE_LICENSE("GPL");
> > +MODULE_AUTHOR("Shiraz Hashim <shiraz.hashim@st.com>");
> > +MODULE_AUTHOR("Viresh Kumar <viresh.kumar@linaro.com>");
> 
> I don't think this works: the second entry will replace the first. Have
> you verified that both authors appear in the output of modinfo?

This is the output of modinfo (compiled for linux-3.5)

$ modinfo pwm-spear.ko
filename:       drivers/pwm/pwm-spear.ko
alias:          platform:st-pwm
author:         Viresh Kumar <viresh.kumar@linaro.com>
author:         Shiraz Hashim <shiraz.hashim@st.com>
license:        GPL
alias:          of:N*T*Cst,spear13xx-pwm*
alias:          of:N*T*Cst,spear-pwm*
depends:        
intree:         Y
vermagic:       3.5.0-test-00138-g08e3584 SMP mod_unload modversions ARMv7 p2v8 


> > +MODULE_ALIAS("platform:st-pwm");
> 
> Should this not rather be "platform:spear-pwm"?

Yes, I would double check these kind of small issues before
sending patches next time.

--
regards
Shiraz