On Tue, 12 Apr 2016 15:11:18 +0200 Thierry Reding <thierry.red...@gmail.com> wrote:
> On Tue, Apr 12, 2016 at 02:45:08PM +0200, Boris Brezillon wrote: > > On Tue, 12 Apr 2016 14:21:41 +0200 > > Thierry Reding <thierry.red...@gmail.com> wrote: > > > > > On Tue, Apr 12, 2016 at 02:17:18PM +0200, Boris Brezillon wrote: > > > > On Tue, 12 Apr 2016 13:49:04 +0200 > > > > Thierry Reding <thierry.red...@gmail.com> wrote: > > > > > > > > > On Wed, Mar 30, 2016 at 10:03:38PM +0200, Boris Brezillon wrote: > > > > > > The PWM state, represented by its period, duty_cycle and polarity, > > > > > > is currently directly stored in the PWM device. > > > > > > Declare a pwm_state structure embedding those field so that we can > > > > > > later > > > > > > use this struct to atomically update all the PWM parameters at once. > > > > > > > > > > > > All pwm_get_xxx() helpers are now implemented as wrappers around > > > > > > pwm_get_state(). > > > > > > > > > > > > Signed-off-by: Boris Brezillon <boris.brezil...@free-electrons.com> > > > > > > --- > > > > > > drivers/pwm/core.c | 8 ++++---- > > > > > > include/linux/pwm.h | 54 > > > > > > +++++++++++++++++++++++++++++++++++++++++------------ > > > > > > 2 files changed, 46 insertions(+), 16 deletions(-) > > > > > > > > > > > > diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c > > > > > > index 6433059..f3f91e7 100644 > > > > > > --- a/drivers/pwm/core.c > > > > > > +++ b/drivers/pwm/core.c > > > > > > @@ -268,7 +268,7 @@ int pwmchip_add_with_polarity(struct pwm_chip > > > > > > *chip, > > > > > > pwm->chip = chip; > > > > > > pwm->pwm = chip->base + i; > > > > > > pwm->hwpwm = i; > > > > > > - pwm->polarity = polarity; > > > > > > + pwm->state.polarity = polarity; > > > > > > > > > > Would this not more correctly be assigned to pwm->args.polarity? After > > > > > all this is setting up the "initial" state, much like DT or the lookup > > > > > tables would for duty cycle and period. > > > > > > > > Yes, I wasn't sure about the pwm_add_with_polarity() meaning. To me, > > > > all the reference info should be extracted from DT, PWM lookup table or > > > > driver specific ->request() implementation, but I can definitely > > > > initialize the args.polarity here too. > > > > > > > > Should I keep the pwm->state.polarity assignment (to set the initial > > > > polarity when the driver does not support hardware readout)? > > > > > > Wouldn't this work automatically as part of the pwm_apply_args() helper > > > if we extended it with this setting? > > > > Well, as you explained in you answer to patch 5, pwm_apply_args() > > should be called on a per-request basis (each time a PWM device is > > requested), while the initial polarity setting should only be applied > > when registering the PWM chip (and its devices). After that, the > > framework takes care of keeping the PWM state in sync with the hardware > > state. > > > > Let's take a real (though a bit unusual) example. Say you have a single > > PWM device referenced by two different users. Only one user can be > > enabled at a time, but each of them has its own reference config > > (different polarity, different period). > > > > User1 calls pwm_get() and applies its own polarity and period. Then > > user1 is unregistered and release the PWM device, leaving the polarity > > and period untouched. > > > > User2 is registered and request the same PWM device, but user2 is > > smarter and tries to extract the current PWM state before adapting the > > config according to pwm_args. If you just reset pwm->state.polarity > > each time pwm_apply_args() is called (and you suggested to call it as > > part of the request procedure), then this means the PWM state is no > > longer in sync with the hardware state. > > In that case neither will be the period or duty cycle. Essentially this > gets us back to square one where we need to decide how to handle current > state vs. initial arguments. That's not true. Now we clearly differentiate the reference config (content of pwm_args which is only a subset of what you'll find in pwm_state) and the PWM state (represented by pwm_state). We should be safe as long as we keep those 2 elements as 2 orthogonal concepts: - pwm_args is supposed to give some hint to the PWM user to help him configure it's PWM appropriately - pwm_state is here to reflect the real PWM state, and apply new configs > > But I don't think this is really going to be an issue because this is > all moot until we've moved over to the atomic API, at which point this > is all going to go away anyway. As stated in my answer to patch 5, I think I misunderstood your suggestion. pwm_apply_args() is supposed to adjust the PWM config to match the period and polarity specified in pwm_args, right? If that's the case, my question is, should we really call this function each time a new user requests a PWM instead of letting those users call the function on-demand (not all users want to adapt the current PWM config to the pwm_args, some may just want to apply a completely new config). -- Boris Brezillon, Free Electrons Embedded Linux and Kernel engineering http://free-electrons.com -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
