DRM Inquiry

Jani Nikula jani.nikula at linux.intel.com
Thu May 24 11:23:27 UTC 2018

On Thu, 24 May 2018, John Sledge <john_sledget at yahoo.com> wrote:
> I was able to update my kernel to 4.6 which has the DRM_DP_AUX_CHARDEV
> in the Kconfig file linux-4.6\drivers\gpu\drm. Though I also
> add DRM_DP_AUX_CHARDEV=y in  kernel config. When invoke uname -r, I
> could see that the kernel is now 4.6.

If you're updating kernels, why not update to a recent kernel that's
actually supported...?

> How can I verify the DRM_DP_AUX_CHARDEV takes effect or got configure
> it correctly?

Boot the kernel, run 'ls /dev/drm_dp_aux*'. If you see stuff, you got it

> It still unclear to me how to follow what you mean by using DRM DP AUX
> interface and getting /dev/drm_dp_auxN node(s) that allows me to read
> and write arbitrary DPCD offsets. 

The device is a char device you can open, seek to an offset (which would
be the DPCD offset), and read. For testing, you can achieve the same
using dd.


Jani Nikula, Intel Open Source Graphics Center

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