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

[Sean Young]

On Fri, Dec 04, 2020 at 12:21:15PM +0100, Uwe Kleine-König wrote:
> Hello Lino,
> 
> On Fri, Dec 04, 2020 at 12:42:15AM +0100, Lino Sanfilippo wrote:
> > On 29.11.20 at 19:10, Uwe Kleine-König wrote:
> > > 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;
> 
> I'd make value an unsigned long long and check for > 0xffffffff instead
> of repeating the (expensive) division. (Hmm, maybe the compiler is smart
> enough to not actually repeat it, but still.)

I wonder where you got that idea from.


Sean