Messages in this thread | | | Date | Fri, 07 Aug 2020 09:28:31 +0200 | From | Michael Walle <> | Subject | Re: [PATCH v7 06/13] pwm: add support for sl28cpld PWM controller |
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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);
-michael
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