Am 28.07.2017 um 11:55 schrieb Volker Vogelhuber:
Hi,
On 24 July 2017 at 14:56, Volker Vogelhuber
<v.vogelhuber@xxxxxxxxxxxxxxxxxxx> wrote:
I wonder if it is possible to have drmModeAddFB2 to handle
'X', 'R', '3', '0' at all. So is this supported in any way?
Secondly, you're correct that you would need (theoretically) to extend
drmModeAddFB2, however it already has DRM_FORMAT_XRGB2101010 and
DRM_FORMAT_XBGR2101010 for i965 and above, which covers everything in
the last 10 years. This is the 'XR30' FourCC you mention, so it should
already be there and working in the kernel.
This question probably better fits to the drm mailing list, although the
discussion started on the mesa list.
I got it working now that my 10bit buffers are correctly displayed
on a Samsung QM49F via drmModeAddFB2 and the 'X', 'R', '3', '0'
fourcc code. Based on the Samsung's datasheet it should support 10bit
signals, although the EDID does not seem to contain a vendor
specific data block that would confirm that assumption.
I have connected an Apollo Lake module with a display port cable
to that display but I'm unsure if it's really 10bit or if there is some
conversion logic somewhere in between that may downsample my
10 bit buffer to 8bit before sending it via displayport to the display.
Well you could just try to display a 10bit image with a gradient going
from black to white.
The difference between 8bit and 10bit should be obvious even to the
naked eye.
Christian.
So far I stumbled over some patches regarding color management
in the drm part of the kernel, but couldn't figure out how one could
configure what is really send to the display. It seem to mostly be
used to manipulate gamma values and so on. As the only indicator
what is provided to the display is the buffer format handled by
drmModeAddFB2 I doubt this is enough to configure the signal.
Otherwise one could argue that the link speed of the display signal
would have to toggle every time I send a different buffer format,
which is certainly not the case. So what portion of the kms/drm chain
do I
miss currently? The drmModeModeInfo pointer has a clock field, but I
guess this is meant to be for the pixel clock not the clock of the
serialized signal. Probably that's why I couldn't find modelines for
4k@60 especially for 10bit compared to 8bit.
Thanks
Volker
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