[PATCH 00/18] drm/vc4: hdmi: Add Support for the YUV output

[Neil Armstrong]

On 18/03/2021 19:16, Jernej Škrabec wrote:
> Hi!
> 
> Dne sreda, 17. marec 2021 ob 16:43:34 CET je Maxime Ripard napisal(a):
>> Hi,
>>
>> Here's an attempt at support the HDMI YUV output on the BCM2711 SoC found on
>> the RaspberryPi4.
>>
>> I took the same approach than what dw-hdmi did already, turning a bunch of
>> functions found in that driver into helpers since they were fairly generic.
>>
>> However, it feels a bit clunky overall and there's a few rough edges that
>> should be addressed in a generic manner:
>>
>>   - while the format negociation makes sense for a bridge, it feels a bit
>>     over-engineered for a simple encoder where that setting could be a 
> simple
>>     switch (and possibly a property?)
> 
> Property could work, but possible values should be then limited to cross 
> section of HW and connected display capabilities.
> 
>>
>>   - more importantly, whether we're choosing an YUV output or not is 
> completely
>>     hidden away from the userspace even though it might have some effect on 
> the
>>     visual quality output (thinking about YUV420 and YUV422 here mostly).
> 
> IMO driver should select highest achievable quality. So in case of YUV420 and 
> YUV422, later should be selected. This should be the case even if the property 
> is implemented.
> 
> Best regards,
> Jernej
> 
>>
>>   - Similarly, the list we report is static and the userspace cannot change 
> or
>>     force one mode over the other. We will always pick YUV444 over RGB444 if
>>     both are available for example.
>>
>> While the first one might just be due to a lack of helpers, the second and
>> third ones are also feeling a bit inconsistent with how we're handling the
>> 10/12 bit output for example

Another points for YUV422 and YUV420 are:
- mandatory YUV420 for pre-HDMI2 displays to achieve 4k60 with HDMI1.4 max TDMS
- possibility to achieve factorial frequencies for 10/12bits, it's not the case for YUV422, it's the same TMDS character rate for 8, 19, 12 and 16bits
- selecting YUV422 instead of YUV444 for 10/12/16 for 4k60 in HDMI2.0

Today we do not take in account the SCDC feedback from the display, but at some point we should
monitor the Scrambling_Status and Character Error Detection to lower down from YUV444 to 422 and 420
for example.

Neil

>>
>> Let me know what you think,
>> Maxime
>>
>> Maxime Ripard (18):
>>   drm: Introduce new HDMI helpers
>>   drm/bridge: Add HDMI output fmt helper
>>   drm/bridge: dw-hdmi: Use helpers
>>   drm/vc4: txp: Properly set the possible_crtcs mask
>>   drm/vc4: crtc: Skip the TXP
>>   drm/vc4: Rework the encoder retrieval code
>>   drm/vc4: hdmi: Add full range RGB helper
>>   drm/vc4: hdmi: Use full range helper in csc functions
>>   drm/vc4: hdmi: Remove limited_rgb_range
>>   drm/vc4: hdmi: Convert to bridge
>>   drm/vc4: hdmi: Move XBAR setup to csc_setup
>>   drm/vc4: hdmi: Replace CSC_CTL hardcoded value by defines
>>   drm/vc4: hdmi: Define colorspace matrices
>>   drm/vc4: hdmi: Change CSC callback prototype
>>   drm/vc4: hdmi: Rework the infoframe prototype
>>   drm/vc4: hdmi: Support HDMI YUV output
>>   drm/vc4: hdmi: Move the pixel rate calculation to a helper
>>   drm/vc4: hdmi: Force YUV422 if the rate is too high
>>
>>  drivers/gpu/drm/Makefile                  |   2 +-
>>  drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 268 ++-------------
>>  drivers/gpu/drm/drm_bridge.c              | 118 +++++++
>>  drivers/gpu/drm/drm_hdmi.c                | 170 +++++++++
>>  drivers/gpu/drm/vc4/vc4_crtc.c            |  59 +++-
>>  drivers/gpu/drm/vc4/vc4_drv.c             |  41 +++
>>  drivers/gpu/drm/vc4/vc4_drv.h             |  26 +-
>>  drivers/gpu/drm/vc4/vc4_hdmi.c            | 399 +++++++++++++++-------
>>  drivers/gpu/drm/vc4/vc4_hdmi.h            |  13 +-
>>  drivers/gpu/drm/vc4/vc4_hdmi_regs.h       |   6 +
>>  drivers/gpu/drm/vc4/vc4_regs.h            |  19 ++
>>  drivers/gpu/drm/vc4/vc4_txp.c             |   2 +-
>>  include/drm/drm_bridge.h                  |   6 +
>>  include/drm/drm_hdmi.h                    |  24 ++
>>  14 files changed, 770 insertions(+), 383 deletions(-)
>>  create mode 100644 drivers/gpu/drm/drm_hdmi.c
>>  create mode 100644 include/drm/drm_hdmi.h
>>
>> -- 
>> 2.30.2
>>
>>
> 
>