libdrm to read/write drm_dpcd helper functions.

Jani Nikula jani.nikula at
Fri May 25 08:39:24 UTC 2018

On Fri, 25 May 2018, lester magtagad <lester.magtagad at> wrote:
> Hello everyone,
> I am new to DRM and linux, I started reading developers guide and research
> on my own.
> I don't know where to start on how to communicate the DP helper functions
> (drm_dp_dpcd_read,  drm_dp_dpcd_readb,  drm_dp_dpcd_write,
> drm_dp_dpcd_writeb),
> what will I include(#include<sample.h>) in my main program. I already have
> drm in my setup(kernel version:4.4.21-69), I also have libdrm-2.4.92 API  ,
> the problem is I don't really have an idea on how use it.
> My main objective is I want to read and write brightness/backlight level on
> DP connections.
> Is it possible to use only the libdrm api to import DP helper functions?if
> yes how?
> Maybe someone can help/guide me on this?

Where does the sudden interest with DPCD access from userspace come
from? See the thread [1]. My replies there should cover this.

I'm starting to wonder if this is an XY problem...



Jani Nikula, Intel Open Source Graphics Center

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