Messages in this thread | | | Subject | Re: [PATCH] leds: leds-pca963x: workaround group blink scaling issue | From | Jacek Anaszewski <> | Date | Tue, 18 Oct 2016 16:17:18 +0200 |
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On 10/18/2016 03:49 PM, Rob Herring wrote: > 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@atomide.com> wrote: >>>> * Jacek Anaszewski <j.anaszewski@samsung.com> [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@samsung.com> 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.
Thanks for the feedback. I infer that you wouldn't mind if I added your ack to this commit then?
-- Best regards, Jacek Anaszewski
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