[PATCH 4/8] drm/vc4: hdmi: Check and warn if we can't reach 4kp60 frequencies

[Dave Stevenson]

Hi Maxime

On Thu, 25 Feb 2021 at 15:59, Maxime Ripard <maxime at cerno.tech> wrote:
>
> In order to reach the frequencies needed to output at 594MHz, the
> firmware needs to be configured with the appropriate parameters in the
> config.txt file (enable_hdmi_4kp60 and force_turbo).

force_turbo isn't the right way to go about this as it permanently
bumps all the clocks up, even if running the display at VGA.

> Let's detect it at bind time, warn the user if we can't, and filter out
> the relevant modes.
>
> Signed-off-by: Maxime Ripard <maxime at cerno.tech>
> ---
>  drivers/gpu/drm/vc4/vc4_hdmi.c | 17 +++++++++++++++++
>  drivers/gpu/drm/vc4/vc4_hdmi.h |  8 ++++++++
>  2 files changed, 25 insertions(+)
>
> diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.c b/drivers/gpu/drm/vc4/vc4_hdmi.c
> index b5bc742993a4..f05f6da286f7 100644
> --- a/drivers/gpu/drm/vc4/vc4_hdmi.c
> +++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
> @@ -953,6 +953,9 @@ static int vc4_hdmi_encoder_atomic_check(struct drm_encoder *encoder,
>         if (pixel_rate > vc4_hdmi->variant->max_pixel_clock)
>                 return -EINVAL;
>
> +       if (vc4_hdmi->disable_4kp60 && (pixel_rate > HDMI_14_MAX_TMDS_CLK))
> +               return -EINVAL;
> +
>         vc4_state->pixel_rate = pixel_rate;
>
>         return 0;
> @@ -972,6 +975,9 @@ vc4_hdmi_encoder_mode_valid(struct drm_encoder *encoder,
>         if ((mode->clock * 1000) > vc4_hdmi->variant->max_pixel_clock)
>                 return MODE_CLOCK_HIGH;
>
> +       if (vc4_hdmi->disable_4kp60 && ((mode->clock * 1000) > HDMI_14_MAX_TMDS_CLK))
> +               return MODE_CLOCK_HIGH;
> +
>         return MODE_OK;
>  }
>
> @@ -1986,6 +1992,17 @@ static int vc4_hdmi_bind(struct device *dev, struct device *master, void *data)
>         vc4_hdmi->disable_wifi_frequencies =
>                 of_property_read_bool(dev->of_node, "wifi-2.4ghz-coexistence");
>
> +       if (variant->max_pixel_clock == 600000000) {
> +               struct vc4_dev *vc4 = to_vc4_dev(drm);
> +               long max_rate = clk_get_max_rate(vc4->hvs->core_clk);
> +
> +               if (max_rate < 550000000) {
> +                       drm_warn(drm, "The core clock cannot reach frequencies high enough to support 4k @ 60Hz.");
> +                       drm_warn(drm, "Please change your config.txt file to add hdmi_enable_4kp60 and force_turbo");

Do we really want to warn in bind? Again you could have a VGA
resolution monitor attached but that would trigger this warning.
Can we warn (once) on processing the mode list and filtering out a clk
> HDMI_14_MAX_TMDS_CLK mode instead?

And mentioning force_turbo is again wrong.

  Dave

> +                       vc4_hdmi->disable_4kp60 = true;
> +               }
> +       }
> +
>         if (vc4_hdmi->variant->reset)
>                 vc4_hdmi->variant->reset(vc4_hdmi);
>
> diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.h b/drivers/gpu/drm/vc4/vc4_hdmi.h
> index 3cebd1fd00fc..3cd021136402 100644
> --- a/drivers/gpu/drm/vc4/vc4_hdmi.h
> +++ b/drivers/gpu/drm/vc4/vc4_hdmi.h
> @@ -154,6 +154,14 @@ struct vc4_hdmi {
>          */
>         bool disable_wifi_frequencies;
>
> +       /*
> +        * Even if HDMI0 on the RPi4 can output modes requiring a pixel
> +        * rate higher than 297MHz, it needs some adjustments in the
> +        * config.txt file to be able to do so and thus won't always be
> +        * available.
> +        */
> +       bool disable_4kp60;
> +
>         struct cec_adapter *cec_adap;
>         struct cec_msg cec_rx_msg;
>         bool cec_tx_ok;
> --
> 2.29.2
>