Dear all, This patch series is a second RFC to know your opinion about the way to solve the problems exposed in the first RFC [1] The first patch what tries to solve is the problem of granularity for high resolution PWMs. The idea is simple interpolate between 2 brightness values so we can have a high PWM duty cycle (a 16 bits PWM is up to 65535 possible steps) without having to list out every possible value in the dts. I think that this patch is required to not break backward compability, to be more flexible and also extend the functionality to be able to use high resolution PWM with enough steps to have a good UI experience in userspace. The second patch is a bit more ambicious, the idea is let decide the driver the brightness-levels required in function of the PWM resolution. To do this we use a static table filled with the CIE 1931 algorithm values to convert brightness to PWM duty cycle. More detailed info is available in the commit message of every patch. A couple of questions come to my mind: - What's the amoung of steps we really need? Currently there is 1024 steps for a resolution of 16 bits, and 37 steps for a PWM with 8 bits of resolution. That seems to work well with both 16 bits and 8 bits. Tested on a Samsung Chromebook Plus (16 bits) and a SL50 device (8 bits) - What about 32 bits or greather resolutions? We need to support it? I did a quick look and seems nobody requires it, but I don't really know. For now if we set more than 16 bits of resolution the driver triggers an error. Waiting for your feedback. Chances since v1: - Add linear interpolation for high resolution PWM. - Get rid of fixed point calculations and use a table instead. [1] http://www.spinics.net/lists/devicetree/msg193262.html Best regards, Enric Balletbo i Serra (2): backlight: pwm_bl: linear interpolation between values of brightness-levels backlight: pwm_bl: compute brightness of LED linearly to human eye. .../bindings/leds/backlight/pwm-backlight.txt | 2 + drivers/video/backlight/pwm_bl.c | 209 ++++++++++++++++++--- include/linux/pwm_backlight.h | 3 + 3 files changed, 191 insertions(+), 23 deletions(-) -- 2.9.3 -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
