SAMA5D27-SOM1-EK1 DRM Mode Settings

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kengineer
Posts: 15
Joined: Tue Oct 31, 2017 3:08 pm

SAMA5D27-SOM1-EK1 DRM Mode Settings

Thu Feb 08, 2018 9:02 pm

I was wondering if there was a tool for setting LCD parameters in the drm_display_mode device structures defined in panel-simple.c. I am making adjustments to a new LCD and it would be much faster to change timing values (hdisplay, hsync_start, etc) on the fly rather than recompiling the kernel each time and re-testing.

If not, I'm guessing there is a way to do with with an ioctl to the DRM system, but wasn't sure which one would be used to get and put these values.

I saw the examples with modetest on the linux4sam site, but these seem to only be used to retrieve data or initiate test patterns on the display, not actually set timing values.
nferre
Site Admin
Posts: 186
Joined: Wed Feb 14, 2007 11:17 am

Re: SAMA5D27-SOM1-EK1 DRM Mode Settings

Mon Feb 12, 2018 12:31 pm

Hi

Setting the timings is done in panel-simple.c as you said.
There is an ongoing initiative to amend those timings in DT, but I don't know if it will go upstream:
https://lists.freedesktop.org/archives/ ... 64886.html

v3 is here: https://lists.freedesktop.org/archives/ ... 65162.html
kengineer
Posts: 15
Joined: Tue Oct 31, 2017 3:08 pm

Re: SAMA5D27-SOM1-EK1 DRM Mode Settings

Thu Feb 22, 2018 6:23 pm

Yeah I'm new to device tree and I was quite surprised when I found out that the timing values were still specified in the kernel itself.


I found an easier way to configure this which is to use the busybox tool devmem2 to manually write the registers until the right settings are obtained.

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