Re: [PATCH v2] pwm: bcm2835: Support apply function for atomic configuration

[Lino Sanfilippo <LinoSanfilippo@gmx.de>]

Hi Uwe,

First off, thanks for the review!

On 29.11.20 at 19:10, Uwe Kleine-König wrote:

>
> Changelog between review rounds go to below the tripple-dash below.
>

Right, will do so in the next patch version.

>
> You're storing an unsigned long long (i.e. 64 bits) in an u32. If
> you are sure that this won't discard relevant bits, please explain
> this in a comment for the cursory reader.

What about an extra check then to make sure that the period has not been truncated,
e.g:

	value = DIV_ROUND_CLOSEST_ULL(state->period, scaler);

	/* dont accept a period that is too small or has been truncated */
	if ((value < PERIOD_MIN) ||
	    (value != DIV_ROUND_CLOSEST_ULL(state->period, scaler)))
		return -EINVAL;


> Also note that round_closed is probably wrong, as .apply() is
> supposed to round down the period to the next achievable period. (But
> fixing this has to do done in a separate patch.)

According to commit 11fc4edc4 rounding to the closest integer has been introduced
to improve precision in case that the pwm controller is used by the pwm-ir-tx driver.
I dont know how strong the requirement is to round down the period in apply(), but I
can imagine that this may be a good reason to deviate from this rule.
(CCing Sean Young who introduced DIV_ROUND_CLOSEST)

Regards,
Lino