When I connected my cubieboard running 4.15-rc1 to my 4k display I got no
picture. Some digging found that there is no check against the upper
pixelclock limit of the HDMI output, so X selects a 4kp60 format at 594
MHz, which obviously won't work.
The patch below adds a check for the upper bound of what this hardware can
do, and it checks if the requested tmds clock can be obtained.
It also allows for the +/- 0.5% pixel clock variation that the HDMI spec permits.
That code is based on commit 22d0be2a55 ("drm: arcpgu: Allow some clock
deviation in crtc->mode_valid() callback") from Jose Abreu for drm/arc.
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Thanks-to: Jose Abreu <Jose.Abreu@synopsys.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Link: https://patchwork.freedesktop.org/patch/msgid/162854cb-c7bd-d9ce-9fa0-9a6cd89c621b@xs4all.nl
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