Re: [PATCH v6 09/15] drm/rockchip: vop2: Use TMDS character rate to select DCLK source

[Daniel Stone]

On Thu, 5 Nov 2026 at 01:01, Cristian Ciocaltea
<cristian.ciocaltea@xxxxxxxxxxxxx> wrote:
> The HDMI PHY PLL can only be used as DCLK source while the HDMI link
> operates in TMDS mode, i.e. for TMDS character rates up to 600 MHz.
> Beyond that, HDMI 2.1 FRL is required, in which case the PLL would run
> at the link rate and VOP2 must keep using the system CRU.
>
> Currently, this is decided by reconstructing the TMDS character rate
> from the DCLK rate and the color depth, i.e. DCLK * bpc / 8, which does
> not hold for all possible output configurations:
>
> - YUV422 always transmits two 12-bit components per clock cycle,
>   regardless of the color depth, which from a clock-rate perspective is
>   equivalent to three 8-bit RGB components.  For example, 4K@60Hz 10-bit
>   YUV422 requires the same bandwidth as 4K@60Hz 8-bit RGB, typically 594
>   MHz.  However, VOP2 wrongly assumes it needs 742.5 MHz (594 * 10 / 8)
>   and ends up switching the DCLK source.  As a consequence, modes
>   requiring uncommon pixel clocks, such as those corresponding to
>   fractional refresh rates, will fail.  An example is 3840x2160@59.94Hz,
>   which would likely rely on a 593.407 MHz clock rate, unsupported by
>   the system CRU.
>
> - When VOP2 processes multiple pixels per clock cycle, DCLK is only a
>   fraction of the pixel clock, e.g. RK3576 halves it for pixel clocks
>   above 600 MHz.  Hence, an FRL mode such as 4K@120Hz 8-bit RGB, with a
>   pixel clock of 1188 MHz, ends up with a 594 MHz DCLK, which slips
>   under the limit and wrongly selects the HDMI PHY PLL as DCLK source.
>
> In preparation for supporting the use cases above, rework the DCLK
> source switch logic to check the TMDS character rate computed by the
> HDMI connector state helpers, which already accounts for the output
> color format and depth.  Keep using the system CRU when the rate is not
> available.
>
> While at it, drop the VOP2_MAX_DCLK_RATE define in favor of the generic
> HDMI_2_0_TMDS_CHAR_RATE_MAX_HZ, since the 600 MHz limit applies to the
> TMDS character rate rather than to DCLK.

Reviewed-by: Daniel Stone <daniels@xxxxxxxxxxxxx>