linux-kernel - Re: [PATCH] drm/meson: fix TMDS clock filtering for DMT monitors

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Message-ID: <CAMO6naz5bqq7_S_y4yFR-ALinB3ApoE3z3m_fymP2RbaqRotAQ@mail.gmail.com>
Date:   Wed, 20 Mar 2019 10:04:57 +0100
From:   Maxime Jourdan <mjourdan@...libre.com>
To:     Neil Armstrong <narmstrong@...libre.com>
Cc:     Daniel Vetter <daniel@...ll.ch>, dri-devel@...ts.freedesktop.org,
        linux-amlogic@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/meson: fix TMDS clock filtering for DMT monitors

Hi Neil,
On Wed, Mar 20, 2019 at 9:11 AM Neil Armstrong <narmstrong@...libre.com> wrote:
>
> DMT monitors does not necessarely report a maximum TMDS clock
> in a VSDB EDID extension.
>
> In this case, all modes are wrongly rejected, including
> the DRM fallback EDID.
>
> This patch only rejects modes whith clock > max_tmds_clock if
> the max_tmds_clock is specified. This will only reject
> 4:2:0 HDMI2.0 modes, who reports a clock > max_tmds_clock.
>
> Reported-by: Maxime Jourdan <mjourdan@...libre.com>
> Fixes: d7d8fb7046b6 ("drm/meson: add HDMI div40 TMDS mode")
> Signed-off-by: Neil Armstrong <narmstrong@...libre.com>
> ---
>  drivers/gpu/drm/meson/meson_dw_hdmi.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/meson/meson_dw_hdmi.c b/drivers/gpu/drm/meson/meson_dw_hdmi.c
> index e28814f4ea6c..563953ec6ad0 100644
> --- a/drivers/gpu/drm/meson/meson_dw_hdmi.c
> +++ b/drivers/gpu/drm/meson/meson_dw_hdmi.c
> @@ -569,7 +569,8 @@ dw_hdmi_mode_valid(struct drm_connector *connector,
>         DRM_DEBUG_DRIVER("Modeline " DRM_MODE_FMT "\n", DRM_MODE_ARG(mode));
>
>         /* If sink max TMDS clock, we reject the mode */
> -       if (mode->clock > connector->display_info.max_tmds_clock)
> +       if (connector->display_info.max_tmds_clock &&
> +           mode->clock > connector->display_info.max_tmds_clock)
>                 return MODE_BAD;
>
>         /* Check against non-VIC supported modes */
> --
> 2.21.0
>

Thanks, this patch restores HDMI output with my old 1080p TV which
does not specify a max tmds clock in its EDID. (all modes were
considered BAD before).

Tested-by: Maxime Jourdan <mjourdan@...libre.com>
Reviewed-by: Maxime Jourdan <mjourdan@...libre.com>