On Wed, 12 Dec 2012 12:31:45 +0100 Thierry Reding <thierry.red...@avionic-design.de> wrote:
> On Wed, Dec 12, 2012 at 07:24:30PM +1100, 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. > > I'd prefer some kind of description about the driver here. I'm not really sure what more there is to say. There was a bit of text in a comment at the top of the file which I've copied to the commit comment. > Also the > subject should be something like: > > pwm: Add OMAP support using dual-mode timers > > or > > pwm: omap: Add PWM support using dual-mode timers Done - I chose the second. > > I take this description to mean that OMAP doesn't have dedicated PWM > hardware? Otherwise it might be bad to call this pwm-omap. Correct. The timers can be used for a number of things which explicitly includes PWM. > > Also please use all-caps when referring to PWM devices in prose. A few > other comments inline below. OK. > > > Cc: Grant Erickson <maratho...@gmail.com> > > Signed-off-by: NeilBrown <ne...@suse.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" > > "OMAP PWM support" Fixed. > > > diff --git a/drivers/pwm/pwm-omap.c b/drivers/pwm/pwm-omap.c > [...] > > + * 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. > > I don't know if this is such a good idea. Usually you number platform > devices sequentially, while this would leave gaps in the numbering. I > know that adding platform data may sound a bit like overkill, but I > really think the added clarity and consistency is worth it. I guess so. No other PWM driver seems to use platform data, and I needed so little... I'll see what I can do. > > > +#define pr_fmt(fmt) "pwm-omap: " fmt > > You don't seem to be using any of the pr_*() logging functions, so this > isn't needed. Gone now, thanks. > > > +#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> > > + > > +#define DM_TIMER_LOAD_MIN 0xFFFFFFFE > > + > > +struct omap_chip { > > + struct platform_device *pdev; > > I don't see this field being used anywhere. No. Gone. > > > + struct omap_dm_timer *dm_timer; > > + unsigned int polarity; > > The PWM subsystem already has enum pwm_polarity for this. > I'll use that then .... and as there is a pwm_set_polarity() interface, that probably means that I don't need to configure the polarity via the platform data? That would be a lot cleaner. > > + const char *label; > > This isn't used anywhere either. Gone. > > > + > > + 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) > > This is never used. :-) There is a theme here. > > > + > > +/** > > + * pwm_calc_value - determines the counter value for a clock rate and > > period. > > Nit: You should either start the sentence with a capital or not > terminate it with a full stop. In this case the sentence really includes the function name which is case-sensitive so cannot be capitalised ;-) I'll rephrase a bit and find something to capitalise. > > > + * @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. > > "compute" Yep. > > > + * > > + * 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; > > Maybe use NSEC_PER_SEC instead? Good idea, thanks. > > > + int cycles; > > + __u64 c; > > I think for in-kernel use, the custom is to stick with simply u64. It is, yes. > > > + > > + c = (__u64)clk_rate * ns; > > + do_div(c, nanoseconds_per_second); > > + cycles = c; > > + > > + return DM_TIMER_LOAD_MIN - cycles; > > Can't you just do "DM_TIMER_LOAD_MIN - c" and get rid of the cycles > variable altogether? Yep. > > > +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. > > + */ > > Block comments should be in the following format: > > /* > * foo... > * bar... > */ OK, I fixed all of those. > > > + > > + 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); > > So omap_dm_timer_disable() doesn't actually stop the timer? It just > disables the access to the registers? > > > + return status; > > "return 0;" and drop the status variable. > Done. > > +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; > > This one can be dropped as well. > > > + const bool enable = true; > > + const bool autoreload = true; > > + const bool toggle = true; > > + const int trigger = OMAP_TIMER_TRIGGER_OVERFLOW_AND_COMPARE; > > I understand that these extra variables are supposed to "document" the > parameters of the functions below. I'm not a huge fan of this approach > because instead the API would better be designed to make it obvious what > the parameters are. Or people can just look at the prototypes to find > out the meaning. But if you really prefer this way I won't object. I've removed the 'trigger' const as the name is self-descriptive. I might leave the others. > > > + int load_value, match_value; > > + unsigned long clk_rate; > > + > > + dev_dbg(chip->dev, > > + "duty cycle: %d, period %d\n", > > + duty_ns, period_ns); > > This all fits on a single line, so no need to break it up. Indeed. > > > + > > + if (omap->duty_ns == duty_ns && > > + omap->period_ns == period_ns) > > + /* No change - don't cause any transients */ > > + return 0; > > Note to self: this might be a candidate to put in the core. might be useful, though the core doesn't currently "know" the current values. > > > + 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. > > + */ > > Again wrong block comment style. > > > + > > + 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 > > + */ > > And here as well. While at it you might want to terminate the last > sentence with a full stop. > I check the sentences in other comments too. > > + pwm_disable(pwm); > > + > > + omap_dm_timer_enable(omap->dm_timer); > > + > > + 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); > > Again this doesn't need so much wrapping. > Nope. > > + > > + omap_dm_timer_set_pwm(omap->dm_timer, > > + !omap->polarity, > > + toggle, > > + trigger); > > This doesn't either. Also you should be explicit about the polarity > parameter, since enum pwm_polarity is an enum and therefore negating it > isn't very nice (it should work though). > > You could solve this by doing something like: > > if (omap->polarity == PWM_POLARITY_NORMAL) > polarity = 1; > else > polarity = 0; (omap->polarity == PWM_POLARITY_NORMAL) would have the same effect. > > > + /* 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. > > + */ > > Also wrong style. > > > + omap_dm_timer_disable(omap->dm_timer); > > + omap->duty_ns = duty_ns; > > + omap->period_ns = period_ns; > > + > > + return status; > > "return 0;" > > > +} > > + > > + > > Gratuitous newline. > > > +static struct pwm_ops omap_pwm_ops = { > > Should be "static const". > > > + .enable = omap_pwm_enable, > > + .disable= omap_pwm_disable, > > There should be a space between .disable and =. OK. > > > + .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. > > + */ > > I'm not sure how useful this kerneldoc comment really is. It isn't about > an exported function and developers usually know what the .probe() does. True. Gone. > > > +static int __devinit omap_pwm_probe(struct platform_device *pdev) > > No more __devinit, please. If you say so (having no idea what it did :-) > > > +{ > > + 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 */ > > I've said this before, I don't think it's a good idea. > > > + > > + omap = kzalloc(sizeof(struct pwm_device), GFP_KERNEL); > > + > > Gratuituous newline. > > > + 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. > > + */ > > Block comment style again. > > > + > > + omap->dm_timer = omap_dm_timer_request_specific(timer); > > + > > Gratuitous newline. Gone. > > > + 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. > > + */ > > And again. > > > + > > + 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. > > + */ > > And again. =) > > > + > > + 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; > > This can just be "return 0;". Yep. > > > + > > + 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) > > No __devexit, please. > > > +{ > > + struct omap_chip *omap = platform_get_drvdata(pdev); > > + int status = 0; > > Just drop this. > > > + > > + status = pwmchip_remove(&omap->chip); > > + if (status < 0) > > + goto done; > > "return status;" Fixed. > > > + > > + omap_dm_timer_free(omap->dm_timer); > > + > > + kfree(omap); > > + > > + done: > > + return status; > > Just "return 0;". No label required. > > > +} > > + > > +#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; > > + > > + return 0; > > +} > > +#else > > +#define omap_pwm_suspend NULL > > +#endif > > This doesn't look right. You should implement .resume() if you really > care, in which case the resume callback would have to reconfigure with > the cached values. In that case maybe you should switch to dev_pm_ops > and SIMPLE_DEV_PM_OPS() as well. > > If you don't, just resetting these values will not make the PWM work > properly after resume either since it will have to be explicitly > reconfigured. I just copied that from pwm-samsung.c I think the point is to avoid the "no transients" short-circuit in omap_pwm_config if the config is unchanged. The assumption is that pwm_disable() will be called before suspend and pwm_config()/pwm_enable() after resume. So there is no point actually configuring anything in .resume() - it makes sense to wait until pwm_config() is called (if ever). But we want to make sure that pwm_config actually does something. But yes, I should change to dev_pm_ops. > > > +static struct platform_driver omap_pwm_driver = { > > + .driver.name = "omap-pwm", > > + .driver.owner = THIS_MODULE, > > The more idiomatic way of writing this is: > > .driver = { > .name = "omap-pwm", > .owner = THIS_MODULE, > }, > I guess... though I think my way is a lot neater. But conformity is good. > > + .probe = omap_pwm_probe, > > + .remove = __devexit_p(omap_pwm_remove), > > No __devexit_p anymore. > OK. > > + .suspend = omap_pwm_suspend, > > + .resume = NULL, > > +}; > > + > > +static int __init omap_pwm_init(void) > > +{ > > + return platform_driver_register(&omap_pwm_driver); > > +} > > + > > +static void __exit omap_pwm_exit(void) > > +{ > > + platform_driver_unregister(&omap_pwm_driver); > > +} > > + > > +arch_initcall(omap_pwm_init); > > This should probably be module_init() instead. You already return > -EPROBE_DEFER if the dual-mode timer isn't ready yet so you should bite > the bullet and get all the dependencies to behave properly as well. New > code shouldn't be using this kind of dependency handling. > > In that case you could also just run module_platform_driver(). > > Thierry > > > +module_exit(omap_pwm_exit); > > + > > +MODULE_AUTHOR("Grant Erickson <maratho...@gmail.com>"); > > +MODULE_AUTHOR("NeilBrown <ne...@suse.de>"); > > Shouldn't this be "Neil Brown"? I noticed you use the concatenated form > in the email address as well, so maybe that's on purpose? Yes, it is on purpose. With a surname like "Brown", one likes finding ways to be distinctive :-) > > > +MODULE_LICENSE("GPLv2"); > > This should be "GPL v2". Maybe MODULE_DESCRIPTION() would be nice too. Fixed. > > Thierry Thanks for your very thorough review! I'll send an updated version once I've resolved other comments and tested again. NeilBrown
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