Hi Boris,
On Wed, Jun 22, 2016 at 10:04 AM, Boris Brezillon
<boris.brezillon@xxxxxxxxxxxxxxxxxx> wrote:
> On Tue, 21 Jun 2016 11:37:31 -0700
> Brian Norris <briannorris@xxxxxxxxxxxx> wrote:
>> On Tue, Jun 21, 2016 at 04:42:04PM +0200, Geert Uytterhoeven wrote:
>> > On Fri, May 27, 2016 at 6:45 PM, Brian Norris <briannorris@xxxxxxxxxxxx> wrote:
>> > > It seems like in the process of refactoring pwm_config() to utilize the
>> > > newly-introduced pwm_apply_state() API, some args/bounds checking was
>> > > dropped.
>> > >
>> > > In particular, I noted that we are now allowing invalid period
>> > > selections. e.g.:
>> > >
>> > > # echo 1 > /sys/class/pwm/pwmchip0/export
>> > > # cat /sys/class/pwm/pwmchip0/pwm1/period
>> > > 100
>> > > # echo 101 > /sys/class/pwm/pwmchip0/pwm1/duty_cycle
>> > > [... driver may or may not reject the value, or trigger some logic bug ...]
>> > >
>> > > It's better to see:
>> > >
>> > > # echo 1 > /sys/class/pwm/pwmchip0/export
>> > > # cat /sys/class/pwm/pwmchip0/pwm1/period
>> > > 100
>> > > # echo 101 > /sys/class/pwm/pwmchip0/pwm1/duty_cycle
>> > > -bash: echo: write error: Invalid argument
>> > >
>> > > This patch reintroduces some bounds checks in both pwm_config() (for its
>> > > signed parameters; we don't want to convert negative values into large
>> > > unsigned values) and in pwm_apply_state() (which fix the above described
>> > > behavior, as well as other potential API misuses).
>> > >
>> > > Fixes: 5ec803edcb70 ("pwm: Add core infrastructure to allow atomic updates")
>> > > Signed-off-by: Brian Norris <briannorris@xxxxxxxxxxxx>
>> > > ---
>> > > v2:
>> > > * changed subject, as this covers more scope now
>> > > * add Fixes tag, as this is a v4.7-rc regression
>> > > * add more bounds/args checks in pwm_apply_state() and pwm_config()
>> > >
>> > > drivers/pwm/core.c | 3 ++-
>> > > include/linux/pwm.h | 3 +++
>> > > 2 files changed, 5 insertions(+), 1 deletion(-)
>> > >
>> > > diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c
>> > > index dba3843c53b8..ed337a8c34ab 100644
>> > > --- a/drivers/pwm/core.c
>> > > +++ b/drivers/pwm/core.c
>> > > @@ -457,7 +457,8 @@ int pwm_apply_state(struct pwm_device *pwm, struct pwm_state *state)
>> > > {
>> > > int err;
>> > >
>> > > - if (!pwm)
>> > > + if (!pwm || !state || !state->period ||
>> > > + state->duty_cycle > state->period)
>> > > return -EINVAL;
>> >
>> > This check breaks the LCD backlight on r8a7740/armadillo.
>> I'm not sure I 100% understand this debug log, but I think maybe the
>> problem is in pwm_apply_args(), which calls pwm_disable() and
>> pwm_set_polarity() sequentially, without ever configuring a period? What
>> if pwm_apply_args() were to configure the period for us?
>>
>> Boris, any thoughts?
>>
>
> I had second thoughts and I think you're right: pwm_apply_args()
> should set the pargs.period period for us.
>
> Here is a patch addressing that.
>
> Geert, can you test it?
>
> --->8---
> From 0610f7e24976e176054bce20445ff42d8aea9513 Mon Sep 17 00:00:00 2001
> From: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxxxxxxx>
> Date: Wed, 22 Jun 2016 09:25:14 +0200
> Subject: [PATCH] pwm: Fix pwm_apply_args()
>
> Commit 5ec803edcb70 ("pwm: Add core infrastructure to allow atomic
> updates"), implemented pwm_disable() as a wrapper around
> pwm_apply_state(), and then, commit ef2bf4997f7d ("pwm: Improve args
> checking in pwm_apply_state()") added missing checks on the ->period
> value in pwm_apply_state() to ensure we were not passing inappropriate
> values to the ->config() or ->apply() methods.
>
> The conjunction of these 2 commits led to a case where pwm_disable()
> was no longer succeeding, thus preventing the polarity setting done
> in pwm_apply_args().
>
> Set a valid period in pwm_apply_args() to ensure polarity setting
> won't be rejected.
>
> Signed-off-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxxxxxxx>
> Reported-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
> Suggested-by: Brian Norris <briannorris@xxxxxxxxxxxx>
> Fixes: 5ec803edcb70 ("pwm: Add core infrastructure to allow atomic updates")
Tested-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
