Re: [PATCH v2] pwm: improve args checking in pwm_apply_state()

Re: [PATCH v2] pwm: improve args checking in pwm_apply_state()

[Geert Uytterhoeven]

Hi Brian,

On Fri, May 27, 2016 at 6:45 PM, Brian Norris <briannorris@chromium.org> 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@chromium.org>
> ---
> 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.
Apparently both period and duty_cycle are zero during the first invocation.
Later, these are initialized from DT, cfr.

        pwms = <&tpu 2 33333 PWM_POLARITY_INVERTED>;

in arch/arm/boot/dts/r8a7740-armadillo800eva.dts.

With added debug printing, the difference between failure and success is:

 renesas-tpu-pwm e6600000.pwm: TPU PWM -1 registered
 tpu_pwm_request:223
 pwm_apply_state:460: pwm backlight/2: period 0, duty_cycle 0
+Ignoring failure
+pwm_apply_state:479: polarity 0 -> 1
+tpu_pwm_set_polarity:343
+pwm_apply_state:502: period 0 -> 0
+pwm_apply_state:503: duty_cycle 0 -> 0
+pwm_apply_state:516: enabled 0 -> 0
 pwm_config:238: pwm backlight/2: duty_ns 33333, period_ns 33333
 pwm_apply_state:460: pwm backlight/2: period 33333, duty_cycle 33333
-pwm_apply_state:479: polarity 0 -> 0
+pwm_apply_state:479: polarity 1 -> 1
 pwm_apply_state:502: period 0 -> 33333
 pwm_apply_state:503: duty_cycle 0 -> 33333
 tpu_pwm_config:267
 pwm_apply_state:516: enabled 0 -> 0
 pwm_apply_state:460: pwm backlight/2: period 33333, duty_cycle 33333
-pwm_apply_state:479: polarity 0 -> 0
+pwm_apply_state:479: polarity 1 -> 1
 pwm_apply_state:502: period 33333 -> 33333
 pwm_apply_state:503: duty_cycle 33333 -> 33333
 pwm_apply_state:516: enabled 0 -> 1
 tpu_pwm_enable:354

Sorry for not noticing last week, before it hit mainline.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

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

Re: [PATCH v2] pwm: improve args checking in pwm_apply_state()

[Brian Norris]

Hi Geert,

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@chromium.org> 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@chromium.org>
> > ---
> > 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.
> Apparently both period and duty_cycle are zero during the first invocation.
> Later, these are initialized from DT, cfr.
> 
>         pwms = <&tpu 2 33333 PWM_POLARITY_INVERTED>;
> 
> in arch/arm/boot/dts/r8a7740-armadillo800eva.dts.

Hmm, this isn't super obvious how to best fix. On one hand, the
pwm_config() API used to reject period<=0, but on the other hand, I
think its replacement (pwm_apply_state()) is getting used in more places
than it used to be, and not all of them are really handling the "atomic
update" concept yet. Seems like a product of Boris's multi-phase attempt
to convert the PWM APIs to support atomic updates -- and many users
haven't really converted yet.

> With added debug printing, the difference between failure and success is:
> 
>  renesas-tpu-pwm e6600000.pwm: TPU PWM -1 registered
>  tpu_pwm_request:223
>  pwm_apply_state:460: pwm backlight/2: period 0, duty_cycle 0
> +Ignoring failure
> +pwm_apply_state:479: polarity 0 -> 1
> +tpu_pwm_set_polarity:343
> +pwm_apply_state:502: period 0 -> 0
> +pwm_apply_state:503: duty_cycle 0 -> 0
> +pwm_apply_state:516: enabled 0 -> 0
>  pwm_config:238: pwm backlight/2: duty_ns 33333, period_ns 33333
>  pwm_apply_state:460: pwm backlight/2: period 33333, duty_cycle 33333
> -pwm_apply_state:479: polarity 0 -> 0
> +pwm_apply_state:479: polarity 1 -> 1
>  pwm_apply_state:502: period 0 -> 33333
>  pwm_apply_state:503: duty_cycle 0 -> 33333
>  tpu_pwm_config:267
>  pwm_apply_state:516: enabled 0 -> 0
>  pwm_apply_state:460: pwm backlight/2: period 33333, duty_cycle 33333
> -pwm_apply_state:479: polarity 0 -> 0
> +pwm_apply_state:479: polarity 1 -> 1
>  pwm_apply_state:502: period 33333 -> 33333
>  pwm_apply_state:503: duty_cycle 33333 -> 33333
>  pwm_apply_state:516: enabled 0 -> 1
>  tpu_pwm_enable:354

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?

> Sorry for not noticing last week, before it hit mainline.

Sorry for the regression :(

Brian

Re: [PATCH v2] pwm: improve args checking in pwm_apply_state()

[Boris Brezillon]

On Tue, 21 Jun 2016 11:37:31 -0700
Brian Norris <briannorris@chromium.org> wrote:

> Hi Geert,
> 
> 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@chromium.org> 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@chromium.org>
> > > ---
> > > 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.
> > Apparently both period and duty_cycle are zero during the first invocation.
> > Later, these are initialized from DT, cfr.
> > 
> >         pwms = <&tpu 2 33333 PWM_POLARITY_INVERTED>;
> > 
> > in arch/arm/boot/dts/r8a7740-armadillo800eva.dts.  
> 
> Hmm, this isn't super obvious how to best fix. On one hand, the
> pwm_config() API used to reject period<=0, but on the other hand, I
> think its replacement (pwm_apply_state()) is getting used in more places
> than it used to be, and not all of them are really handling the "atomic
> update" concept yet. Seems like a product of Boris's multi-phase attempt
> to convert the PWM APIs to support atomic updates -- and many users
> haven't really converted yet.
> 
> > With added debug printing, the difference between failure and success is:
> > 
> >  renesas-tpu-pwm e6600000.pwm: TPU PWM -1 registered
> >  tpu_pwm_request:223
> >  pwm_apply_state:460: pwm backlight/2: period 0, duty_cycle 0
> > +Ignoring failure
> > +pwm_apply_state:479: polarity 0 -> 1
> > +tpu_pwm_set_polarity:343
> > +pwm_apply_state:502: period 0 -> 0
> > +pwm_apply_state:503: duty_cycle 0 -> 0
> > +pwm_apply_state:516: enabled 0 -> 0
> >  pwm_config:238: pwm backlight/2: duty_ns 33333, period_ns 33333
> >  pwm_apply_state:460: pwm backlight/2: period 33333, duty_cycle 33333
> > -pwm_apply_state:479: polarity 0 -> 0
> > +pwm_apply_state:479: polarity 1 -> 1
> >  pwm_apply_state:502: period 0 -> 33333
> >  pwm_apply_state:503: duty_cycle 0 -> 33333
> >  tpu_pwm_config:267
> >  pwm_apply_state:516: enabled 0 -> 0
> >  pwm_apply_state:460: pwm backlight/2: period 33333, duty_cycle 33333
> > -pwm_apply_state:479: polarity 0 -> 0
> > +pwm_apply_state:479: polarity 1 -> 1
> >  pwm_apply_state:502: period 33333 -> 33333
> >  pwm_apply_state:503: duty_cycle 33333 -> 33333
> >  pwm_apply_state:516: enabled 0 -> 1
> >  tpu_pwm_enable:354  
> 
> 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 think this is partly caused by this commit:

a8c3862551e0 ("pwm: Keep PWM state in sync with hardware state")

But again, we need that one if we don't want to override the current
PWM period with the pwm_args one when the driver support hardware
readout.

This leaves 2 choices:

1/ assign the period to pargs->period if ->get_state() is not
   implemented
2/ remove the !period check in pwm_apply_state() when state->enabled is
   false (do we really care if period = 0 when all we want to do is
   disable the PWM?)

Thierry, what's you're opinion.

Re: [PATCH v2] pwm: improve args checking in pwm_apply_state()

[Boris Brezillon]

On Tue, 21 Jun 2016 11:37:31 -0700
Brian Norris <briannorris@chromium.org> wrote:

> Hi Geert,
> 
> 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@chromium.org> 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@chromium.org>
> > > ---
> > > 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.
> > Apparently both period and duty_cycle are zero during the first invocation.
> > Later, these are initialized from DT, cfr.
> > 
> >         pwms = <&tpu 2 33333 PWM_POLARITY_INVERTED>;
> > 
> > in arch/arm/boot/dts/r8a7740-armadillo800eva.dts.  
> 
> Hmm, this isn't super obvious how to best fix. On one hand, the
> pwm_config() API used to reject period<=0, but on the other hand, I
> think its replacement (pwm_apply_state()) is getting used in more places
> than it used to be, and not all of them are really handling the "atomic
> update" concept yet. Seems like a product of Boris's multi-phase attempt
> to convert the PWM APIs to support atomic updates -- and many users
> haven't really converted yet.
> 
> > With added debug printing, the difference between failure and success is:
> > 
> >  renesas-tpu-pwm e6600000.pwm: TPU PWM -1 registered
> >  tpu_pwm_request:223
> >  pwm_apply_state:460: pwm backlight/2: period 0, duty_cycle 0
> > +Ignoring failure
> > +pwm_apply_state:479: polarity 0 -> 1
> > +tpu_pwm_set_polarity:343
> > +pwm_apply_state:502: period 0 -> 0
> > +pwm_apply_state:503: duty_cycle 0 -> 0
> > +pwm_apply_state:516: enabled 0 -> 0
> >  pwm_config:238: pwm backlight/2: duty_ns 33333, period_ns 33333
> >  pwm_apply_state:460: pwm backlight/2: period 33333, duty_cycle 33333
> > -pwm_apply_state:479: polarity 0 -> 0
> > +pwm_apply_state:479: polarity 1 -> 1
> >  pwm_apply_state:502: period 0 -> 33333
> >  pwm_apply_state:503: duty_cycle 0 -> 33333
> >  tpu_pwm_config:267
> >  pwm_apply_state:516: enabled 0 -> 0
> >  pwm_apply_state:460: pwm backlight/2: period 33333, duty_cycle 33333
> > -pwm_apply_state:479: polarity 0 -> 0
> > +pwm_apply_state:479: polarity 1 -> 1
> >  pwm_apply_state:502: period 33333 -> 33333
> >  pwm_apply_state:503: duty_cycle 33333 -> 33333
> >  pwm_apply_state:516: enabled 0 -> 1
> >  tpu_pwm_enable:354  
> 
> 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@free-electrons.com>
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@free-electrons.com>
Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Suggested-by: Brian Norris <briannorris@chromium.org>
Fixes: 5ec803edcb70 ("pwm: Add core infrastructure to allow atomic updates")
---
 include/linux/pwm.h | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/include/linux/pwm.h b/include/linux/pwm.h
index 908b67c847cd..c038ae36b10e 100644
--- a/include/linux/pwm.h
+++ b/include/linux/pwm.h
@@ -464,6 +464,8 @@ static inline bool pwm_can_sleep(struct pwm_device *pwm)
 
 static inline void pwm_apply_args(struct pwm_device *pwm)
 {
+	struct pwm_state state = { };
+
 	/*
 	 * PWM users calling pwm_apply_args() expect to have a fresh config
 	 * where the polarity and period are set according to pwm_args info.
@@ -476,18 +478,20 @@ static inline void pwm_apply_args(struct pwm_device *pwm)
 	 * at startup (even if they are actually enabled), thus authorizing
 	 * polarity setting.
 	 *
-	 * Instead of setting ->enabled to false, we call pwm_disable()
-	 * before pwm_set_polarity() to ensure that everything is configured
-	 * as expected, and the PWM is really disabled when the user request
-	 * it.
+	 * To fulfill this requirement, we apply a new state which disables
+	 * the PWM device and set the reference period and polarity config.
 	 *
 	 * Note that PWM users requiring a smooth handover between the
 	 * bootloader and the kernel (like critical regulators controlled by
 	 * PWM devices) will have to switch to the atomic API and avoid calling
 	 * pwm_apply_args().
 	 */
-	pwm_disable(pwm);
-	pwm_set_polarity(pwm, pwm->args.polarity);
+
+	state.enabled = false;
+	state.polarity = pwm->args.polarity;
+	state.period = pwm->args.period;
+
+	pwm_apply_state(pwm, &state);
 }
 
 struct pwm_lookup {
-- 
2.7.4

Re: [PATCH v2] pwm: improve args checking in pwm_apply_state()

[Thierry Reding]

[-- Attachment #1: Type: text/plain, Size: 8120 bytes --]

On Wed, Jun 22, 2016 at 10:04:22AM +0200, Boris Brezillon wrote:
> On Tue, 21 Jun 2016 11:37:31 -0700
> Brian Norris <briannorris@chromium.org> wrote:
> 
> > Hi Geert,
> > 
> > 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@chromium.org> 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@chromium.org>
> > > > ---
> > > > 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.
> > > Apparently both period and duty_cycle are zero during the first invocation.
> > > Later, these are initialized from DT, cfr.
> > > 
> > >         pwms = <&tpu 2 33333 PWM_POLARITY_INVERTED>;
> > > 
> > > in arch/arm/boot/dts/r8a7740-armadillo800eva.dts.  
> > 
> > Hmm, this isn't super obvious how to best fix. On one hand, the
> > pwm_config() API used to reject period<=0, but on the other hand, I
> > think its replacement (pwm_apply_state()) is getting used in more places
> > than it used to be, and not all of them are really handling the "atomic
> > update" concept yet. Seems like a product of Boris's multi-phase attempt
> > to convert the PWM APIs to support atomic updates -- and many users
> > haven't really converted yet.
> > 
> > > With added debug printing, the difference between failure and success is:
> > > 
> > >  renesas-tpu-pwm e6600000.pwm: TPU PWM -1 registered
> > >  tpu_pwm_request:223
> > >  pwm_apply_state:460: pwm backlight/2: period 0, duty_cycle 0
> > > +Ignoring failure
> > > +pwm_apply_state:479: polarity 0 -> 1
> > > +tpu_pwm_set_polarity:343
> > > +pwm_apply_state:502: period 0 -> 0
> > > +pwm_apply_state:503: duty_cycle 0 -> 0
> > > +pwm_apply_state:516: enabled 0 -> 0
> > >  pwm_config:238: pwm backlight/2: duty_ns 33333, period_ns 33333
> > >  pwm_apply_state:460: pwm backlight/2: period 33333, duty_cycle 33333
> > > -pwm_apply_state:479: polarity 0 -> 0
> > > +pwm_apply_state:479: polarity 1 -> 1
> > >  pwm_apply_state:502: period 0 -> 33333
> > >  pwm_apply_state:503: duty_cycle 0 -> 33333
> > >  tpu_pwm_config:267
> > >  pwm_apply_state:516: enabled 0 -> 0
> > >  pwm_apply_state:460: pwm backlight/2: period 33333, duty_cycle 33333
> > > -pwm_apply_state:479: polarity 0 -> 0
> > > +pwm_apply_state:479: polarity 1 -> 1
> > >  pwm_apply_state:502: period 33333 -> 33333
> > >  pwm_apply_state:503: duty_cycle 33333 -> 33333
> > >  pwm_apply_state:516: enabled 0 -> 1
> > >  tpu_pwm_enable:354  
> > 
> > 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@free-electrons.com>
> 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@free-electrons.com>
> Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
> Suggested-by: Brian Norris <briannorris@chromium.org>
> Fixes: 5ec803edcb70 ("pwm: Add core infrastructure to allow atomic updates")
> ---
>  include/linux/pwm.h | 16 ++++++++++------
>  1 file changed, 10 insertions(+), 6 deletions(-)
> 
> diff --git a/include/linux/pwm.h b/include/linux/pwm.h
> index 908b67c847cd..c038ae36b10e 100644
> --- a/include/linux/pwm.h
> +++ b/include/linux/pwm.h
> @@ -464,6 +464,8 @@ static inline bool pwm_can_sleep(struct pwm_device *pwm)
>  
>  static inline void pwm_apply_args(struct pwm_device *pwm)
>  {
> +	struct pwm_state state = { };
> +
>  	/*
>  	 * PWM users calling pwm_apply_args() expect to have a fresh config
>  	 * where the polarity and period are set according to pwm_args info.
> @@ -476,18 +478,20 @@ static inline void pwm_apply_args(struct pwm_device *pwm)
>  	 * at startup (even if they are actually enabled), thus authorizing
>  	 * polarity setting.
>  	 *
> -	 * Instead of setting ->enabled to false, we call pwm_disable()
> -	 * before pwm_set_polarity() to ensure that everything is configured
> -	 * as expected, and the PWM is really disabled when the user request
> -	 * it.
> +	 * To fulfill this requirement, we apply a new state which disables
> +	 * the PWM device and set the reference period and polarity config.
>  	 *
>  	 * Note that PWM users requiring a smooth handover between the
>  	 * bootloader and the kernel (like critical regulators controlled by
>  	 * PWM devices) will have to switch to the atomic API and avoid calling
>  	 * pwm_apply_args().
>  	 */
> -	pwm_disable(pwm);
> -	pwm_set_polarity(pwm, pwm->args.polarity);
> +
> +	state.enabled = false;
> +	state.polarity = pwm->args.polarity;
> +	state.period = pwm->args.period;
> +
> +	pwm_apply_state(pwm, &state);
>  }
>  
>  struct pwm_lookup {

This looks reasonable to me. I'll wait for a Tested-by from Geert before
applying, though.

Thierry

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Re: [PATCH v2] pwm: improve args checking in pwm_apply_state()

[Geert Uytterhoeven]

Hi Boris,

On Wed, Jun 22, 2016 at 10:04 AM, Boris Brezillon
<boris.brezillon@free-electrons.com> wrote:
> On Tue, 21 Jun 2016 11:37:31 -0700
> Brian Norris <briannorris@chromium.org> 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@chromium.org> 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@chromium.org>
>> > > ---
>> > > 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@free-electrons.com>
> 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@free-electrons.com>
> Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
> Suggested-by: Brian Norris <briannorris@chromium.org>
> Fixes: 5ec803edcb70 ("pwm: Add core infrastructure to allow atomic updates")

Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

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

Re: [PATCH v2] pwm: improve args checking in pwm_apply_state()

[Brian Norris]

On Wed, Jun 22, 2016 at 10:04:22AM +0200, Boris Brezillon wrote:
> From 0610f7e24976e176054bce20445ff42d8aea9513 Mon Sep 17 00:00:00 2001
> From: Boris Brezillon <boris.brezillon@free-electrons.com>
> 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@free-electrons.com>
> Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
> Suggested-by: Brian Norris <briannorris@chromium.org>
> Fixes: 5ec803edcb70 ("pwm: Add core infrastructure to allow atomic updates")
> ---
>  include/linux/pwm.h | 16 ++++++++++------
>  1 file changed, 10 insertions(+), 6 deletions(-)
> 
> diff --git a/include/linux/pwm.h b/include/linux/pwm.h
> index 908b67c847cd..c038ae36b10e 100644
> --- a/include/linux/pwm.h
> +++ b/include/linux/pwm.h
> @@ -464,6 +464,8 @@ static inline bool pwm_can_sleep(struct pwm_device *pwm)
>  
>  static inline void pwm_apply_args(struct pwm_device *pwm)
>  {
> +	struct pwm_state state = { };
> +
>  	/*
>  	 * PWM users calling pwm_apply_args() expect to have a fresh config
>  	 * where the polarity and period are set according to pwm_args info.
> @@ -476,18 +478,20 @@ static inline void pwm_apply_args(struct pwm_device *pwm)
>  	 * at startup (even if they are actually enabled), thus authorizing
>  	 * polarity setting.
>  	 *
> -	 * Instead of setting ->enabled to false, we call pwm_disable()
> -	 * before pwm_set_polarity() to ensure that everything is configured
> -	 * as expected, and the PWM is really disabled when the user request
> -	 * it.

I was confused by this original text when reading it the first time. I
like the replacement text and implementation, as it seems to make more
sense.

> +	 * To fulfill this requirement, we apply a new state which disables
> +	 * the PWM device and set the reference period and polarity config.
>  	 *
>  	 * Note that PWM users requiring a smooth handover between the
>  	 * bootloader and the kernel (like critical regulators controlled by
>  	 * PWM devices) will have to switch to the atomic API and avoid calling
>  	 * pwm_apply_args().
>  	 */
> -	pwm_disable(pwm);
> -	pwm_set_polarity(pwm, pwm->args.polarity);

Notably, you're dropping the 'if (!pwm) { }' safety checks that are part
of pwm_disable() and pwm_set_polarity(). But I don't think there should
be any users relying on that.

> +
> +	state.enabled = false;
> +	state.polarity = pwm->args.polarity;
> +	state.period = pwm->args.period;
> +
> +	pwm_apply_state(pwm, &state);
>  }
>  
>  struct pwm_lookup {

Reviewed-by: Brian Norris <briannorris@chromium.org>

Re: [PATCH v2] pwm: improve args checking in pwm_apply_state()

[Boris Brezillon]

On Wed, 22 Jun 2016 12:16:59 -0700
Brian Norris <briannorris@chromium.org> wrote:

> On Wed, Jun 22, 2016 at 10:04:22AM +0200, Boris Brezillon wrote:
> > From 0610f7e24976e176054bce20445ff42d8aea9513 Mon Sep 17 00:00:00 2001
> > From: Boris Brezillon <boris.brezillon@free-electrons.com>
> > 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@free-electrons.com>
> > Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
> > Suggested-by: Brian Norris <briannorris@chromium.org>
> > Fixes: 5ec803edcb70 ("pwm: Add core infrastructure to allow atomic updates")
> > ---
> >  include/linux/pwm.h | 16 ++++++++++------
> >  1 file changed, 10 insertions(+), 6 deletions(-)
> > 
> > diff --git a/include/linux/pwm.h b/include/linux/pwm.h
> > index 908b67c847cd..c038ae36b10e 100644
> > --- a/include/linux/pwm.h
> > +++ b/include/linux/pwm.h
> > @@ -464,6 +464,8 @@ static inline bool pwm_can_sleep(struct pwm_device *pwm)
> >  
> >  static inline void pwm_apply_args(struct pwm_device *pwm)
> >  {
> > +	struct pwm_state state = { };
> > +
> >  	/*
> >  	 * PWM users calling pwm_apply_args() expect to have a fresh config
> >  	 * where the polarity and period are set according to pwm_args info.
> > @@ -476,18 +478,20 @@ static inline void pwm_apply_args(struct pwm_device *pwm)
> >  	 * at startup (even if they are actually enabled), thus authorizing
> >  	 * polarity setting.
> >  	 *
> > -	 * Instead of setting ->enabled to false, we call pwm_disable()
> > -	 * before pwm_set_polarity() to ensure that everything is configured
> > -	 * as expected, and the PWM is really disabled when the user request
> > -	 * it.  
> 
> I was confused by this original text when reading it the first time. I
> like the replacement text and implementation, as it seems to make more
> sense.

Well, it should have been done this way from the beginning, but
pwm_apply_args() was introduced before the commit introducing the atomic
APIs, and I forgot to update it when moving to the atomic approach :-/.

> 
> > +	 * To fulfill this requirement, we apply a new state which disables
> > +	 * the PWM device and set the reference period and polarity config.
> >  	 *
> >  	 * Note that PWM users requiring a smooth handover between the
> >  	 * bootloader and the kernel (like critical regulators controlled by
> >  	 * PWM devices) will have to switch to the atomic API and avoid calling
> >  	 * pwm_apply_args().
> >  	 */
> > -	pwm_disable(pwm);
> > -	pwm_set_polarity(pwm, pwm->args.polarity);  
> 
> Notably, you're dropping the 'if (!pwm) { }' safety checks that are part
> of pwm_disable() and pwm_set_polarity(). But I don't think there should
> be any users relying on that.

Indeed. I can add it back here if you prefer, but honestly, PWM users
that are not checking the value returned by pwm_get() should be
considered buggy IMHO, and a NULL pointer exception is a good way to
make people realize they are not properly using the API :).

> 
> > +
> > +	state.enabled = false;
> > +	state.polarity = pwm->args.polarity;
> > +	state.period = pwm->args.period;
> > +
> > +	pwm_apply_state(pwm, &state);
> >  }
> >  
> >  struct pwm_lookup {  
> 
> Reviewed-by: Brian Norris <briannorris@chromium.org>

Re: [PATCH v2] pwm: improve args checking in pwm_apply_state()

[Brian Norris]

On Wed, Jun 22, 2016 at 10:41:14PM +0200, Boris Brezillon wrote:
> On Wed, 22 Jun 2016 12:16:59 -0700
> Brian Norris <briannorris@chromium.org> wrote:
> > Notably, you're dropping the 'if (!pwm) { }' safety checks that are part
> > of pwm_disable() and pwm_set_polarity(). But I don't think there should
> > be any users relying on that.
> 
> Indeed. I can add it back here if you prefer,

Nah, that's ok. I just had to say it anyway :)

> but honestly, PWM users
> that are not checking the value returned by pwm_get() should be
> considered buggy IMHO, and a NULL pointer exception is a good way to
> make people realize they are not properly using the API :).

Seems OK.

Brian

Re: [PATCH v2] pwm: improve args checking in pwm_apply_state()

[Thierry Reding]

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On Wed, Jun 22, 2016 at 01:46:48PM -0700, Brian Norris wrote:
> On Wed, Jun 22, 2016 at 10:41:14PM +0200, Boris Brezillon wrote:
> > On Wed, 22 Jun 2016 12:16:59 -0700
> > Brian Norris <briannorris@chromium.org> wrote:
> > > Notably, you're dropping the 'if (!pwm) { }' safety checks that are part
> > > of pwm_disable() and pwm_set_polarity(). But I don't think there should
> > > be any users relying on that.
> > 
> > Indeed. I can add it back here if you prefer,
> 
> Nah, that's ok. I just had to say it anyway :)
> 
> > but honestly, PWM users
> > that are not checking the value returned by pwm_get() should be
> > considered buggy IMHO, and a NULL pointer exception is a good way to
> > make people realize they are not properly using the API :).
> 
> Seems OK.

I've applied this to my fixes branch, and I'll let it cook in linux-next
for a little while, then send it off to Linus for v4.7-rc6 next week if
no further fallout is caused by this.

Thierry

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