Messages in this thread | | | Subject | Re: [RFC 0/2] backlight: pwm_bl: support linear brightness to human eye | From | Daniel Thompson <> | Date | Tue, 5 Sep 2017 12:09:20 +0100 |
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On 05/09/17 12:05, Daniel Thompson wrote: > On 04/09/17 16:35, Enric Balletbo i Serra wrote: >> Dear all, >> >> This patch series is a first RFC to know your opinion about implement >> support to create brightness levels tables dinamically. I tried to argue >> in every patch the specific reasons we think this can be interesting, to >> sumup, the idea behind these patches is be able to pass via device tree >> two parameters to the driver so it can calculate the brightness levels >> based on the CIE 1931 lightness formula, which is what actually describes >> how we perceive light. >> >> I think that at least the maths involved can be improved, and I've still >> some doubts. With current code if you create a table with a max PWM >> value of 255 and 127 steps, the first numbers are repeated so I'm >> thinking > that maybe we should skip/remove the repeated values. i.e. >> have a table >> like this, >> >> [0, 1, 2, 3 ... 235, 240, 245, 250, 255] >> >> instead of >> >> [0, 0, 0, 1, 1, 1, 1, 2, 2, 2, 2, 2, 3 ... 235, 240, 245, 250, 255] >> >> Well, I know there are things to improve but lets see your feedback first >> before dedicate more time on it. The patches were tested on a couple of >> devices but I'll test on more devices meanwhile we discuss about it. > > I'm not fully decided on this one but my initial reaction isn't to > question the concept so much as to ask why the number of levels should > go in the devicetree at all! We could just make brightness-levels > optional and get the driver to pick sane curves by default. > > I'm sure we can debate what "sane" means for a couple of e-mails yet but > in principle, given it knows the PWM max counter value, the driver > should be able to calculate the "right" number of steps too. If we have > that your core code remains but we don't have to complexify the device
... tree
Sorry. ;-)
Daniel.
> > <strawman> > Basically we prefer X (?100 like some of the Intel DRM drivers do for > connector properties?) steps but we reduce the number of steps if the > PWM is rather course and we can't get sufficiently different steps. > </strawman> > > I guess the summary of what I'm saying is that if we can > programmatically derive brightness curves then the number of steps is > not really a property of the hardware and doesn't belong in devicetree. > > > Daniel.
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