Messages in this thread | | | Date | Wed, 18 Jan 2017 12:00:32 +0100 | From | Thierry Reding <> | Subject | Re: [PATCH] pwm: pca9685: Fix misuse of regmap_update_bits |
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On Wed, Jan 18, 2017 at 11:55:10AM +0100, Thierry Reding wrote: > On Mon, Dec 05, 2016 at 05:34:02PM +0100, Clemens Gruber wrote: > > On Tue, Nov 29, 2016 at 06:02:50PM +0100, Florian Vaussard wrote: > > > Using regmap_update_bits(..., mask, 1) with 'mask' following (1 << k) > > > and k greater than 0 is wrong. Indeed, _regmap_update_bits will perform > > > (mask & 1), which results in 0 if LSB of mask is 0. Thus the call > > > regmap_update_bits(..., mask, 1) is in reality equivalent to > > > regmap_update_bits(..., mask, 0). > > > > > > In such a case, the correct use is regmap_update_bits(..., mask, mask). > > > > > > This driver is performing such a mistake with the MODE1_RESTART mask, > > > which equals (1 << 6). Fix the driver to make it consistent with the > > > API. Please note that this change is untested, as I do not have this > > > piece of hardware. Testers are welcome! > > > > > > Signed-off-by: Florian Vaussard <florian.vaussard@heig-vd.ch> > > > --- > > > drivers/pwm/pwm-pca9685.c | 3 ++- > > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > > > diff --git a/drivers/pwm/pwm-pca9685.c b/drivers/pwm/pwm-pca9685.c > > > index 117fccf..6b9ff6c 100644 > > > --- a/drivers/pwm/pwm-pca9685.c > > > +++ b/drivers/pwm/pwm-pca9685.c > > > @@ -124,7 +124,8 @@ static int pca9685_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm, > > > */ > > > if (duty_ns == pca->duty_ns) { > > > regmap_update_bits(pca->regmap, PCA9685_MODE1, > > > - MODE1_RESTART, 0x1); > > > + MODE1_RESTART, > > > + MODE1_RESTART); > > > return 0; > > > } > > > } else { > > > -- > > > 2.5.5 > > > > Good catch! > > During testing your change however, I noticed that this whole > > conditional for duty_ns == pca->duty_ns (which I added) is bogus: > > Restarting the chip means using the same ON and OFF times as before, so > > the duty cycle "ratio" stays the same, relative to the period. > > Here we are checking for an equal duty cycle in nanoseconds though.. > > > > Instead we would have to check if the ratio changed and only if it did > > not, set the RESTART bit. > > > > Or we could just remove that conditional. This is only an optimization > > for the special case of changing both period_ns and duty_ns at the same > > time but with the same ratio as before. > > So what's the status on this?
Oh wait, that's what these:
http://patchwork.ozlabs.org/patch/705438/ http://patchwork.ozlabs.org/patch/705437/
are fixing, right?
Florian, I take it there's no reason to apply this patch anymore given that Clemens' patch removes this hunk and replaces it with a proper fix for this particular driver?
Thierry [unhandled content-type:application/pgp-signature] | |