Message-ID: <20121213140635.4eda5858@notabene.brown>
Date:	Thu, 13 Dec 2012 14:06:35 +1100
From:	NeilBrown <neilb@...e.de>
To:	Jon Hunter <jon-hunter@...com>
Cc:	Thierry Reding <thierry.reding@...onic-design.de>,
	Grant Erickson <marathon96@...il.com>,
	<linux-omap@...r.kernel.org>, lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] OMAP: add pwm driver using dmtimers.


[Thierry: question for you near the end - thanks]

On Wed, 12 Dec 2012 10:08:28 -0600 Jon Hunter <jon-hunter@...com> wrote:

> Hi Neil,
> 
> On 12/12/2012 02:24 AM, NeilBrown wrote:
> > 
> > 
> > This patch is based on an earlier patch by Grant Erickson
> > which provided pwm devices using the 'legacy' interface.
> > 
> > This driver instead uses the new framework interface.
> > 
> > Cc: Grant Erickson <marathon96@...il.com>
> > Signed-off-by: NeilBrown <neilb@...e.de>
> > 
> > diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
> > index ed81720..7df573a 100644
> > --- a/drivers/pwm/Kconfig
> > +++ b/drivers/pwm/Kconfig
> > @@ -85,6 +85,15 @@ config PWM_MXS
> >  	  To compile this driver as a module, choose M here: the module
> >  	  will be called pwm-mxs.
> >  
> > +config PWM_OMAP
> > +	tristate "OMAP pwm support"
> > +	depends on ARCH_OMAP
> 
> We should probably have depends on or selects OMAP_DM_TIMER here too.

Sounds sensible - fixed.

> 
> > +	help
> > +	  Generic PWM framework driver for OMAP
> > +
> > +	  To compile this driver as a module, choose M here: the module
> > +	  will be called pwm-omap
> > +
> >  config PWM_PUV3
> >  	tristate "PKUnity NetBook-0916 PWM support"
> >  	depends on ARCH_PUV3
> > diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile
> > index acfe482..f5d200d 100644
> > --- a/drivers/pwm/Makefile
> > +++ b/drivers/pwm/Makefile
> > @@ -5,6 +5,7 @@ obj-$(CONFIG_PWM_IMX)		+= pwm-imx.o
> >  obj-$(CONFIG_PWM_JZ4740)	+= pwm-jz4740.o
> >  obj-$(CONFIG_PWM_LPC32XX)	+= pwm-lpc32xx.o
> >  obj-$(CONFIG_PWM_MXS)		+= pwm-mxs.o
> > +obj-$(CONFIG_PWM_OMAP)		+= pwm-omap.o
> >  obj-$(CONFIG_PWM_PUV3)		+= pwm-puv3.o
> >  obj-$(CONFIG_PWM_PXA)		+= pwm-pxa.o
> >  obj-$(CONFIG_PWM_SAMSUNG)	+= pwm-samsung.o
> > diff --git a/drivers/pwm/pwm-omap.c b/drivers/pwm/pwm-omap.c
> > new file mode 100644
> > index 0000000..e3dbce3
> > --- /dev/null
> > +++ b/drivers/pwm/pwm-omap.c
> > @@ -0,0 +1,318 @@
> > +/*
> > + *    Copyright (c) 2012 NeilBrown <neilb@...e.de>
> > + *    Heavily based on earlier code which is:
> > + *    Copyright (c) 2010 Grant Erickson <marathon96@...il.com>
> > + *
> > + *    Also based on pwm-samsung.c
> > + *
> > + *    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.
> > + *
> > + *    Description:
> > + *      This file is the core OMAP2/3 support for the generic, Linux
> 
> I would drop the OMAP2/3 and just say OMAP here. Potentially this should
> work for OMAP1-5.
> 

Done.


> > + *      PWM driver / controller, using the OMAP's dual-mode timers.
> > + *
> > + *    The 'id' number for the device encodes the number of the dm timer
> > + *    to use, and the polarity of the output.
> > + *    lsb is '1' of active-high, and '0' for active low
> > + *    remaining bit a timer number and need to be shifted down before use.
> > + */
> > +
> > +#define pr_fmt(fmt) "pwm-omap: " fmt
> > +
> > +#include <linux/export.h>
> > +#include <linux/kernel.h>
> > +#include <linux/platform_device.h>
> > +#include <linux/slab.h>
> > +#include <linux/err.h>
> > +#include <linux/clk.h>
> > +#include <linux/io.h>
> > +#include <linux/pwm.h>
> > +#include <linux/module.h>
> > +
> > +#include <plat/dmtimer.h>
> 
> This is going to be a problem for the single zImage work, because we
> cannot include any plat headers in driver code any more. Therefore,
> although it is not ideal, one way to handle this is pass function
> pointers to the various dmtimer APIs that are needed via the platform
> data. Painful I know ...

But that doesn't work with devicetree does it?

Can't we move the dmtimer.h file to include/linux/omap-dmtimer.h or something?

It only included other things from include/linux, so it should be safe.

> 
> > +#define DM_TIMER_LOAD_MIN		0xFFFFFFFE
> > +
> > +struct omap_chip {
> > +	struct platform_device	*pdev;
> > +
> > +	struct omap_dm_timer	*dm_timer;
> > +	unsigned int		polarity;
> > +	const char		*label;
> > +
> > +	unsigned int		duty_ns, period_ns;
> > +	struct pwm_chip		chip;
> > +};
> > +
> > +#define to_omap_chip(chip)	container_of(chip, struct omap_chip, chip)
> > +
> > +#define	pwm_dbg(_pwm, msg...) dev_dbg(&(_pwm)->pdev->dev, msg)
> > +
> > +/**
> > + * pwm_calc_value - determines the counter value for a clock rate and period.
> > + * @clk_rate: The clock rate, in Hz, of the PWM's clock source to compute the
> > + *            counter value for.
> > + * @ns: The period, in nanoseconds, to computer the counter value for.
> > + *
> > + * Returns the PWM counter value for the specified clock rate and period.
> > + */
> > +static inline int pwm_calc_value(unsigned long clk_rate, int ns)
> > +{
> > +	const unsigned long nanoseconds_per_second = 1000000000;
> > +	int cycles;
> > +	__u64 c;
> > +
> > +	c = (__u64)clk_rate * ns;
> > +	do_div(c, nanoseconds_per_second);
> > +	cycles = c;
> > +
> > +	return DM_TIMER_LOAD_MIN - cycles;
> > +}
> > +
> > +static int omap_pwm_enable(struct pwm_chip *chip, struct pwm_device *pwm)
> > +{
> > +	struct omap_chip *omap = to_omap_chip(chip);
> > +	int status = 0;
> > +
> > +	/* Enable the counter--always--before attempting to write its
> > +	 * registers and then set the timer to its minimum load value to
> > +	 * ensure we get an overflow event right away once we start it.
> > +	 */
> > +
> > +	omap_dm_timer_enable(omap->dm_timer);
> > +	omap_dm_timer_write_counter(omap->dm_timer, DM_TIMER_LOAD_MIN);
> > +	omap_dm_timer_start(omap->dm_timer);
> > +	omap_dm_timer_disable(omap->dm_timer);
> 
> Why not just use omap_dm_timer_load_start() here instead of the above 4
> APIs?

Because I didn't know about it.  I do now :-)

> 
> > +
> > +	return status;
> > +}
> > +
> > +static void omap_pwm_disable(struct pwm_chip *chip, struct pwm_device *pwm)
> > +{
> > +	struct omap_chip *omap = to_omap_chip(chip);
> > +
> > +	omap_dm_timer_stop(omap->dm_timer);
> > +}
> > +
> > +static int omap_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
> > +			   int duty_ns, int period_ns)
> > +{
> > +	struct omap_chip *omap = to_omap_chip(chip);
> > +	int status = 0;
> > +	const bool enable = true;
> > +	const bool autoreload = true;
> > +	const bool toggle = true;
> > +	const int trigger = OMAP_TIMER_TRIGGER_OVERFLOW_AND_COMPARE;
> > +	int load_value, match_value;
> > +	unsigned long clk_rate;
> > +
> > +	dev_dbg(chip->dev,
> > +		"duty cycle: %d, period %d\n",
> > +		duty_ns, period_ns);
> > +
> > +	if (omap->duty_ns == duty_ns &&
> > +	    omap->period_ns == period_ns)
> > +		/* No change - don't cause any transients */
> > +		return 0;
> > +
> > +	clk_rate = clk_get_rate(omap_dm_timer_get_fclk(omap->dm_timer));
> > +
> > +	/* Calculate the appropriate load and match values based on the
> > +	 * specified period and duty cycle. The load value determines the
> > +	 * cycle time and the match value determines the duty cycle.
> > +	 */
> > +
> > +	load_value = pwm_calc_value(clk_rate, period_ns);
> > +	match_value = pwm_calc_value(clk_rate, period_ns - duty_ns);
> > +
> > +	/* We MUST enable yet stop the associated dual-mode timer before
> > +	 * attempting to write its registers.  Hopefully it is already
> > +	 * disabled, but call the (idempotent) pwm_disable just in case
> > +	 */
> > +
> > +	pwm_disable(pwm);
> > +
> > +	omap_dm_timer_enable(omap->dm_timer);
> 
> Do you need to call omap_dm_timer_enable here? _set_load and _set_match
> will enable the timer. So this should not be necessary.

True.  That is what you get for copying someone else's code and not
understanding it fully.

> 
> > +	omap_dm_timer_set_load(omap->dm_timer, autoreload, load_value);
> > +	omap_dm_timer_set_match(omap->dm_timer, enable, match_value);
> > +
> > +	dev_dbg(chip->dev,
> > +			"load value: %#08x (%d), "
> > +			"match value: %#08x (%d)\n",
> > +			load_value, load_value,
> > +			match_value, match_value);
> > +
> > +	omap_dm_timer_set_pwm(omap->dm_timer,
> > +			      !omap->polarity,
> > +			      toggle,
> > +			      trigger);
> > +
> > +	/* Set the counter to generate an overflow event immediately. */
> > +
> > +	omap_dm_timer_write_counter(omap->dm_timer, DM_TIMER_LOAD_MIN);
> > +
> > +	/* Now that we're done configuring the dual-mode timer, disable it
> > +	 * again. We'll enable and start it later, when requested.
> > +	 */
> > +
> > +	omap_dm_timer_disable(omap->dm_timer);
> 
> Similarly the disable should not be needed here either.
> 
> > +	omap->duty_ns = duty_ns;
> > +	omap->period_ns = period_ns;
> > +
> > +	return status;
> > +}
> > +
> > +
> > +static struct pwm_ops omap_pwm_ops = {
> > +	.enable	= omap_pwm_enable,
> > +	.disable= omap_pwm_disable,
> > +	.config	= omap_pwm_config,
> > +	.owner	= THIS_MODULE,
> > +};
> > +
> > +/**
> > + * omap_pwm_probe - check for the PWM and bind it to the driver.
> > + * @pdev: A pointer to the platform device node associated with the
> > + *        PWM instance to be probed for driver binding.
> > + *
> > + * Returns 0 if the PWM instance was successfully bound to the driver;
> > + * otherwise, < 0 on error.
> > + */
> > +static int __devinit omap_pwm_probe(struct platform_device *pdev)
> 
> I believe that __devinit is no longer required.
> 
> > +{
> > +	struct device *dev = &pdev->dev;
> > +	struct omap_chip *omap;
> > +	int status = 0;
> > +	unsigned int id = pdev->id;
> > +	unsigned int timer = id >> 1; /* lsb is polarity */
> > +
> > +	omap = kzalloc(sizeof(struct pwm_device), GFP_KERNEL);
> > +
> > +	if (omap == NULL) {
> > +		dev_err(dev, "Could not allocate memory.\n");
> > +		status = -ENOMEM;
> > +		goto done;
> > +	}
> > +
> > +	/* Request the OMAP dual-mode timer that will be bound to and
> > +	 * associated with this generic PWM.
> > +	 */
> > +
> > +	omap->dm_timer = omap_dm_timer_request_specific(timer);
> 
> I would recommend that you use omap_dm_timer_request_by_cap() (new for
> v3.8 so you should be able to use once v3.8-rc1 is out) here to request
> a timer that supports the PWM output. The above function will not be
> supported when booting with device-tree.

I wasn't planning on rushing into working on 3.8-rcX so I'd rather not do
this now.
Would you object to the patch being submitted with the current call, then an
update when I do move on to 3.8?

However.... I may be misunderstanding something, but I want a timer to drive
a particular output pin - GPIO-57.  And I thought that it could only be
driver by GPT11.  So I need to explicitly request number 11 don't I?


> 
> > +
> > +	if (omap->dm_timer == NULL) {
> > +		status = -EPROBE_DEFER;
> > +		goto err_free;
> > +	}
> > +
> > +	/* Configure the source for the dual-mode timer backing this
> > +	 * generic PWM device. The clock source will ultimately determine
> > +	 * how small or large the PWM frequency can be.
> > +	 *
> > +	 * At some point, it's probably worth revisiting moving this to
> > +	 * the configure method and choosing either the slow- or
> > +	 * system-clock source as appropriate for the desired PWM period.
> > +	 */
> > +
> > +	omap_dm_timer_set_source(omap->dm_timer, OMAP_TIMER_SRC_SYS_CLK);
> > +
> > +	/* Cache away other miscellaneous driver-private data and state
> > +	 * information and add the driver-private data to the platform
> > +	 * device.
> > +	 */
> > +
> > +	omap->chip.dev = dev;
> > +	omap->chip.ops = &omap_pwm_ops;
> > +	omap->chip.base = -1;
> > +	omap->chip.npwm = 1;
> > +	omap->polarity = id & 1;
> > +
> > +	status = pwmchip_add(&omap->chip);
> > +	if (status < 0) {
> > +		dev_err(dev, "failed to register pwm\n");
> > +		omap_dm_timer_free(omap->dm_timer);
> > +		goto err_free;
> > +	}
> > +
> > +	platform_set_drvdata(pdev, omap);
> > +
> > +	status = 0;
> > +	goto done;
> > +
> > + err_free:
> > +	kfree(omap);
> > + done:
> > +	return status;
> > +}
> > +
> > +/**
> > + * omap_pwm_remove - unbind the specified PWM platform device from the driver.
> > + * @pdev: A pointer to the platform device node associated with the
> > + *        PWM instance to be unbound/removed.
> > + *
> > + * Returns 0 if the PWM was successfully removed as a platform device;
> > + * otherwise, < 0 on error.
> > + */
> > +static int __devexit omap_pwm_remove(struct platform_device *pdev)
> 
> I believe that __devexit is no longer required.
> 
> > +{
> > +	struct omap_chip *omap = platform_get_drvdata(pdev);
> > +	int status = 0;
> > +
> > +	status = pwmchip_remove(&omap->chip);
> > +	if (status < 0)
> > +		goto done;
> > +
> > +	omap_dm_timer_free(omap->dm_timer);
> 
> Is it guaranteed that the timer will be disabled at this point?

Uhmm... it seems that pwm_put() doesn't call pwm_disable(), so I guess it
might not be disabled.
Thierry: should pwm_put do that, or do I need a 'free' function in my chip
ops to do that?


> 
> > +
> > +	kfree(omap);
> > +
> > + done:
> > +	return status;
> > +}
> > +
> > +#if CONFIG_PM
> > +static int omap_pwm_suspend(struct platform_device *pdev, pm_message_t state)
> > +{
> > +	struct omap_chip *omap = platform_get_drvdata(pdev);
> > +	/* No one preserve these values during suspend so reset them
> > +	 * Otherwise driver leaves PWM unconfigured if same values
> > +	 * passed to pwm_config
> > +	 */
> > +	omap->period_ns = 0;
> > +	omap->duty_ns = 0;
> 
> 
> Hmmm, looks like you are trying to force a reconfiguration after suspend
> if the same values are used. Is there an underlying problem here that
> you are trying to workaround?

I copied that from pwm-samsung.c.

The key question is: does a dmtimer preserve all register values over suspend.
If so, then I guess we don't need this.
If not, we do (because omap_pwm_config short circuits if it thinks the config
hasn't changed).

Maybe I should test and see - though as my backlight always blanks before
suspend that might not be straight forward...

> 
> Please note that I am not familiar with the PWM sub-system to know how
> suspend-resume is typically handled and if this is normal or not.
> 
> > +	return 0;
> > +}
> > +#else
> > +#define omap_pwm_suspend	NULL
> > +#endif
> > +
> > +static struct platform_driver omap_pwm_driver = {
> > +	.driver.name	= "omap-pwm",
> > +	.driver.owner	= THIS_MODULE,
> > +	.probe		= omap_pwm_probe,
> > +	.remove		= __devexit_p(omap_pwm_remove),
> 
> I believe that __devexit_p is no longer required.
> 
> Otherwise it looks good to me. Thanks for sending!

And thanks a lot for reading and reviewing!

NeilBrown

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