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
