[Bug 110496] [GLK] no signal - with samsung 4k TV - HDMI UHD Color (ENABLED)

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=110496

--- Comment #27 from shashank.sharma at intel.com <shashank.sharma at intel.com> ---
As I had mentioned previously, I dont have access to this monitor, but based on
the observations shared by everyone, this is what I think is happening: 

- HDMI 2.0 spec can support a max clock of 600Mhz. 
- Samsung TVs with UHD mode of display expect > 8BPC from the source in this
mode of operations. This means you have to at-least drive 10 BPC output from
SOC display. 
- 4K at 60 modes (RGB/YCBCR444) need 597Mhz clock in 8 BPC mode of operation and
will need > 597 Mhz clock to drive 4k at 60 10/12/16 BPC.
- 4K at 30 modes (RGB/YCBCR444) need 297Mhz clock for 8 BPC mode of operation, so
it can even go up-to 16 BPC, which will still be with-in the 600Mhz range.
- YCBCR 4:2:0 needs half the clock, than RGB/YCBCR444 mode of operation. This
means 4K at 60 YCBCR420 output will need a clock of 597 Mhz and which further
means we can drive 4k at 60 10/12/16 BPC with YCBCR420 output, with-in the 600 Mhz
clock range. 

That's why we can see 4k at 30 deep color, 4k at 60 YCBCR 420 deep color outputs
working on this TV, but as soon as we switch to RGB 4k at 60, the driver restricts
the HDMI output to 4k at 60 8BPC, which is being rejected by the TV, in the UHD
mode of operation.

- Shashank

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