Messages in this thread | | | Date | Fri, 07 Aug 2020 09:55:19 +0200 | From | Michael Walle <> | Subject | Re: [PATCH v7 06/13] pwm: add support for sl28cpld PWM controller |
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Am 2020-08-07 09:45, schrieb Uwe Kleine-König: > On Fri, Aug 07, 2020 at 09:28:31AM +0200, Michael Walle wrote: >> Hi Uwe, Hi Lee, >> >> Am 2020-08-06 10:40, schrieb Uwe Kleine-König: >> > On Mon, Aug 03, 2020 at 11:35:52AM +0200, Michael Walle wrote: >> > > diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig >> > > index 7dbcf6973d33..a0d50d70c3b9 100644 >> > > --- a/drivers/pwm/Kconfig >> > > +++ b/drivers/pwm/Kconfig >> > > @@ -428,6 +428,16 @@ config PWM_SIFIVE >> > > To compile this driver as a module, choose M here: the module >> > > will be called pwm-sifive. >> > > >> > > +config PWM_SL28CPLD >> > > + tristate "Kontron sl28cpld PWM support" >> > > + select MFD_SIMPLE_MFD_I2C >> > >> > Is it sensible to present this option to everyone? Maybe >> > >> > depends on SOME_SYMBOL_ONLY_TRUE_ON_SL28CPLD || COMPILE_TEST >> >> Because there is now no real MFD driver anymore, there is also >> no symbol for that. The closest would be ARCH_ARM64 but I don't >> think that is a good idea. >> >> Lee, what do you think about adding a symbol to the MFD, which >> selects MFD_SIMPLE_MFD_I2C but doesn't enable any C modules? >> >> I.e. >> config MFD_SL28CPLD >> tristate "Kontron sl28cpld" >> select MFD_SIMPLE_MFD_I2C >> help >> Say yes here to add support for the Kontron sl28cpld board >> management controller. >> >> Then all the other device driver could depend on the MFD_SL28CPLD >> symbol. >> >> [..] >> >> > > +static void sl28cpld_pwm_get_state(struct pwm_chip *chip, >> > > + struct pwm_device *pwm, >> > > + struct pwm_state *state) >> > > +{ >> > > + struct sl28cpld_pwm *priv = dev_get_drvdata(chip->dev); >> > > + unsigned int reg; >> > > + int prescaler; >> > > + >> > > + sl28cpld_pwm_read(priv, SL28CPLD_PWM_CTRL, ®); >> > > + >> > > + state->enabled = reg & SL28CPLD_PWM_CTRL_ENABLE; >> > > + >> > > + prescaler = FIELD_GET(SL28CPLD_PWM_CTRL_PRESCALER_MASK, reg); >> > > + state->period = SL28CPLD_PWM_PERIOD(prescaler); >> > > + >> > > + sl28cpld_pwm_read(priv, SL28CPLD_PWM_CYCLE, ®); >> > > + state->duty_cycle = SL28CPLD_PWM_TO_DUTY_CYCLE(reg); >> > >> > Should reg be masked to SL28CPLD_PWM_CYCLE_MAX, or is it guaranteed that >> > the upper bits are zero? >> >> Mh, the hardware guarantees that bit7 is zero. So masking with >> SL28CPLD_PWM_CYCLE_MAX won't buy us much. But what I could think >> could go wrong is this: someone set the prescaler to != 0 and the >> duty cycle to a value greater than the max value for this particular >> prescaler mode. For the above calculations this would result in a >> duty_cycle greater than the period, if I'm not mistaken. >> >> The behavior of the hardware is undefined in that case (at the moment >> it will be always on, I guess). So this isn't a valid setting. >> Nevertheless it might happen. So what about the following: >> >> state->duty_cycle = min(state->duty_cycle, state->period); > > If you care about this: This can also happen (at least shortly) in > sl28cpld_pwm_apply() as you write SL28CPLD_PWM_CTRL before > SL28CPLD_PWM_CYCLE there.
It could also happen if it was the other way around, couldn't it? Changing modes might glitch.
I care more about returning valid values to the PWM core ;)
-michael
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