Re: [PATCH] leds: leds-pca963x: workaround group blink scaling issue

[Rob Herring]

On Mon, Oct 17, 2016 at 09:58:26AM +0200, Jacek Anaszewski wrote:
> On 10/15/2016 02:00 PM, Matt Ranostay wrote:
> > On Fri, Oct 14, 2016 at 7:20 AM, Tony Lindgren <tony@xxxxxxxxxxx> wrote:
> > > * Jacek Anaszewski <j.anaszewski@xxxxxxxxxxx> [161013 23:37]:
> > > > On 10/13/2016 04:20 PM, Matt Ranostay wrote:
> > > > > On Thu, Oct 13, 2016 at 4:05 PM, Jacek Anaszewski
> > > > > <j.anaszewski@xxxxxxxxxxx> wrote:
> > > > > > Why DT property? Is it somehow dependent on the board configuration?
> > > > > > How this period-scale value is calculated? Is it inferred empirically?
> > > > > > 
> > > > > 
> > > > > We empirically discovered and verified this with an logic analyzer on
> > > > > multiple batches of this part.
> > > > > Reason for the DT entry is we aren't 100% sure that it is always going
> > > > > to be the same with different board revs.
> > > > > 
> > > > > Could be that parts clock acts differently with supply voltage.   This
> > > > > has been calculated by setting it an expected value, and measuring the
> > > > > actual result with the logic analyzer.
> > > > 
> > > > I'd like to have DT maintainer's ack for this.
> > > > 
> > > > Cc Rob and Mark.
> > > 
> > > How about do this based on the compatible property instead? If there
> > > are multiple manufacturers for this part and only a certain
> > > parts have this issue we should have multiple compatible properties.
> > > 
> > 
> > I could only find that NXP as the manufacturer of that part. It is
> > possible since the clock is internal to the chipset that the vdd of
> > 2.5V is doing something undefined.
> > 
> > > Then if it turns out all of them need this scaling there's no need
> > > to update the binding.
> > 
> > Understandable.
> 
> Since at present we can't guarantee that all produced devices
> are affected, then we should strive to avoid breaking any existing
> users of the possible non-affected devices.
> 
> In view of that the addition of a new "compatible" proposed by Tony
> seems most reasonable.
> 
> Still, DT maintainer's opinion is required.

Seems like a quirk of this board, so I think the added property is fine.

It could be existing users just didn't notice the rate being off. 30% is 
probably not all that noticeable to the human eye.

Rob