Re: [PATCH] drm/meson: encoder_dsi: load ENCL gamma table while ENCL is disabled

[Neil Armstrong <neil.armstrong@linaro.org>]

On 10/4/26 16:50, Shigeaki Asai via B4 Relay wrote:
> From: Shigeaki Asai <y-asai.0816@docomonet.jp>
> 
> meson_encoder_dsi_atomic_enable() programmed the ENCL gamma LUT right
> after meson_venc_mipi_dsi_mode_set(), i.e. while the ENCL timing
> generator was already running (ENCL_VIDEO_EN=1). Writing the LUT
> during active video stalls the hardware: L_GAMMA_CNTL_PORT
> WR_RDY/ADR_RDY deassert and the ENCL line counter (ENCL_INFO_READ)
> freezes, so every remaining write times out (~8s total at boot) and
> the panel ends up with a corrupted gamma table (wrong colors).
> 
> Instrumented boots on the ODROID-GO Ultra (S922X) show:
> 
>    failing:  start: VIDEO_EN=1 INFO 0000001a->002d0000 GAMMA_CNTL=00000030
>              stall: INFO 002d0000->002d0000 GAMMA_CNTL=00000000
>              (VID_CLK_CNTL2 / VIID_CLK_CNTL / VIID_CLK_DIV unchanged,
>               i.e. the ENCL clock is still running)
>    fixed:    start: VIDEO_EN=0 INFO 00000000->00000000 GAMMA_CNTL=00000030
>              no stall, no timeout
> 
> Whether it failed depended only on timing, which is why enabling
> lock debugging (LOCKDEP etc.) appeared to "fix" it most of the time.
> It happens regardless of the bootloader (mainline or Hardkernel vendor
> U-Boot).
> 
> The function already writes ENCL_VIDEO_EN=0 right afterwards before
> re-enabling the encoder, so simply move meson_encl_load_gamma() after
> that write. This matches the order used by the vendor U-Boot's own LCD
> driver, which never times out.
> 
> Tested on the ODROID-GO Ultra with mainline U-Boot: 5 cold boots +
> 3 warm reboots, no timeouts, correct colors, LOCKDEP disabled.
> 
> Fixes: 42dcf15f901c ("drm/meson: add DSI encoder")
> Cc: stable@vger.kernel.org
> Tested-by: John Williams <porschemad911@gmail.com>
> Signed-off-by: Shigeaki Asai <y-asai.0816@docomonet.jp>
> ---
> This was found on the ODROID-GO Ultra while bringing it up on
> Lakka / ROCKNIX. Happy to test any alternative approach.
> ---
>   drivers/gpu/drm/meson/meson_encoder_dsi.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/meson/meson_encoder_dsi.c b/drivers/gpu/drm/meson/meson_encoder_dsi.c
> index faa309cb97a6..912cd676bbe2 100644
> --- a/drivers/gpu/drm/meson/meson_encoder_dsi.c
> +++ b/drivers/gpu/drm/meson/meson_encoder_dsi.c
> @@ -65,9 +65,9 @@ static void meson_encoder_dsi_atomic_enable(struct drm_bridge *bridge,
>   	/* ENCL clock setup is handled by CCF */
>   
>   	meson_venc_mipi_dsi_mode_set(priv, &crtc_state->adjusted_mode);
> -	meson_encl_load_gamma(priv);
>   
>   	writel_relaxed(0, priv->io_base + _REG(ENCL_VIDEO_EN));
> +	meson_encl_load_gamma(priv);
>   
>   	writel_bits_relaxed(ENCL_VIDEO_MODE_ADV_VFIFO_EN, ENCL_VIDEO_MODE_ADV_VFIFO_EN,
>   			    priv->io_base + _REG(ENCL_VIDEO_MODE_ADV));
> 
> ---
> base-commit: 70456f05d4b6396b22048c4b8cd3cb98ecf9f9e3
> change-id: 20261004-meson-gamma-3306257c0d28
> 
> Best regards,
> --
> Shigeaki Asai <y-asai.0816@docomonet.jp>

Thanks for figuring this out !

Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>

Thanks,
Neil