phy: rockchip: samsung-hdptx: Pre-compute HDMI PLL config for 461.10125 MHz output

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Attempting to make use of a 1080p@120Hz display mode with 10 bpc RGB on
my Acer XV275K P3 monitor results in a blank image.  A similar behavior
has been reported on Philips 279M1RV.

The faulty modeline is created by drm_gtf_mode_complex() based on the
following EDID entry from the Standard Timings block:

  GTF:  1920x1080  119.999987 Hz  16:9    138.840 kHz    368.759000 MHz

It's worth noting the computed pixel clock ends up being slightly higher
at 368.881000 MHz.  Nevertheless, this seems to work consistently fine
with 8 bpc RGB.

After switching to 10 bpc, the TMDS character rate expected for the mode
increases to 461.101250 MHz, as per drm_hdmi_compute_mode_clock().

Since there is no entry for this rate in the ropll_tmds_cfg table, the
necessary HDMI PLL configuration parameters are calculated dynamically
by rk_hdptx_phy_clk_pll_calc().  However, the resulting output rate is
not quite a perfect match, i.e. 461.100000 MHz.  That proved to be the
actual root cause of the problem.

Add a new entry to the TMDS configuration table and provide the
necessary frequency division coefficients for the PHY PLL to generate
the expected 461.101250 MHz output.

Fixes: 9d0ec51d7c ("phy: rockchip: samsung-hdptx: Add high color depth management")
Tested-by: Derek Foreman <derek.foreman@collabora.com>
Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
Link: https://patch.msgid.link/20251221-phy-hdptx-pll-fix-v2-1-ae4abf7f75a1@collabora.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>

...

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Cristian Ciocaltea 2025-12-21 12:36:23 +02:00 • committed by Vinod Koul

parent c9d03933ea

commit f2daf0c67a

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drivers/phy/rockchip/phy-rockchip-samsung-hdptx.c

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