On Mon, Nov 16, 2015 at 01:23:59PM +0100, Boris Brezillon wrote:

Mark Brown [off-list ref] wrote:

quoted

On Mon, Nov 16, 2015 at 09:56:32AM +0100, Boris Brezillon wrote:

quoted

quoted

-	pwm_reg_period = pwm_get_period(drvdata->pwm);
+	pwm_reg_period = pwm_get_default_period(drvdata->pwm);

quoted

It's not clear to me that we're not looking for the current period here
or in the other use.  Won't configuring based on a period other than the
one that has been set give the wrong answer?

Hm, maybe that's naming problem. What I call the 'default' period here
is actually the period configured in your board file (using a PWM lookup
table) or your DT. This value represent the period requested by the PWM
user not a default value specified by the PWM chip driver.

The reason we're not using the 'current' period value is because it may
have been set by the bootloader, and may be inappropriate for our use
case (ie. the period may be to small to represent the different
voltages).

ITOH, we're using the current period value when calculating the current
voltage, because we want to get the correct voltage value, and the PWM
device may still use the configuration set by the bootloader (not the
default one specified in your board or DT files).

I hope this clarifies the differences between the current and default
period, and why we should use the default value here.

To be honest I'm still a bit confused here.  When do we actually apply
the default setting and why do we keep on having to constantly override
it rather than doing this once at boot?  It feels wrong to be using it
every time we set anything.  I'd expect it to be something we only need
to do at probe time or which would automatically be handled by the PWM
framework (but that'd have issues changing the state and potentially
breaking things if done in an uncoordiated fashion).