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
<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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