Hi Brian, 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. 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@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