[PATCH] drm/vc4: hdmi: Block odd horizontal timings

[Dave Stevenson]

Hi Maxime

On Fri, 25 Sep 2020 at 14:00, Maxime Ripard <maxime at cerno.tech> wrote:
>
> The FIFO between the pixelvalve and the HDMI controller runs at 2 pixels
> per clock cycle, and cannot deal with odd timings.
>
> Let's reject any mode with such timings.
>
> Signed-off-by: Maxime Ripard <maxime at cerno.tech>

It's unsupported due to the architecture rather than broken.

I'd hope the compiler would convert "% 2" to "& 1" in these cases, but
it's not a critical performance path anyway.

Reviewed-by: Dave Stevenson <dave.stevenson at raspberrypi.com>

> ---
>  drivers/gpu/drm/vc4/vc4_hdmi.c | 12 ++++++++++++
>  drivers/gpu/drm/vc4/vc4_hdmi.h |  3 +++
>  2 files changed, 15 insertions(+)
>
> diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.c b/drivers/gpu/drm/vc4/vc4_hdmi.c
> index 1c4dc774d56e..acfb4e235214 100644
> --- a/drivers/gpu/drm/vc4/vc4_hdmi.c
> +++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
> @@ -879,6 +879,11 @@ static int vc4_hdmi_encoder_atomic_check(struct drm_encoder *encoder,
>         struct vc4_hdmi *vc4_hdmi = encoder_to_vc4_hdmi(encoder);
>         unsigned long long pixel_rate = mode->clock * 1000;
>
> +       if (vc4_hdmi->variant->broken_odd_h_timings &&
> +           ((mode->hdisplay % 2) || (mode->hsync_start % 2) ||
> +            (mode->hsync_end % 2) || (mode->htotal % 2)))
> +               return -EINVAL;
> +
>         if (mode->flags & DRM_MODE_FLAG_DBLCLK)
>                 pixel_rate *= 2;
>
> @@ -901,6 +906,11 @@ vc4_hdmi_encoder_mode_valid(struct drm_encoder *encoder,
>  {
>         struct vc4_hdmi *vc4_hdmi = encoder_to_vc4_hdmi(encoder);
>
> +       if (vc4_hdmi->variant->broken_odd_h_timings &&
> +           ((mode->hdisplay % 2) || (mode->hsync_start % 2) ||
> +            (mode->hsync_end % 2) || (mode->htotal % 2)))
> +               return MODE_H_ILLEGAL;
> +
>         if ((mode->clock * 1000) > vc4_hdmi->variant->max_pixel_clock)
>                 return MODE_CLOCK_HIGH;
>
> @@ -1950,6 +1960,7 @@ static const struct vc4_hdmi_variant bcm2711_hdmi0_variant = {
>                 PHY_LANE_2,
>                 PHY_LANE_CK,
>         },
> +       .broken_odd_h_timings   = true,
>
>         .init_resources         = vc5_hdmi_init_resources,
>         .csc_setup              = vc5_hdmi_csc_setup,
> @@ -1975,6 +1986,7 @@ static const struct vc4_hdmi_variant bcm2711_hdmi1_variant = {
>                 PHY_LANE_CK,
>                 PHY_LANE_2,
>         },
> +       .broken_odd_h_timings   = true,
>
>         .init_resources         = vc5_hdmi_init_resources,
>         .csc_setup              = vc5_hdmi_csc_setup,
> diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.h b/drivers/gpu/drm/vc4/vc4_hdmi.h
> index af45b0d81dec..40e51ece8efe 100644
> --- a/drivers/gpu/drm/vc4/vc4_hdmi.h
> +++ b/drivers/gpu/drm/vc4/vc4_hdmi.h
> @@ -62,6 +62,9 @@ struct vc4_hdmi_variant {
>          */
>         enum vc4_hdmi_phy_channel phy_lane_mapping[4];
>
> +       /* The BCM2711 cannot deal with odd horizontal pixel timings */
> +       bool broken_odd_h_timings;
> +
>         /* Callback to get the resources (memory region, interrupts,
>          * clocks, etc) for that variant.
>          */
> --
> 2.26.2
>