linux-kernel - Re: [PATCH] drm/nouveau/disp: Support more modes by checking with lower bpc

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Message-ID: <CACO55turFB8MNbxB3Vk=J1GK_t07K+Ybym906fR=yDLfnwk8bw@mail.gmail.com>
Date:   Sat, 1 Apr 2023 02:19:34 +0200
From:   Karol Herbst <kherbst@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     Lyude Paul <lyude@...hat.com>, Ben Skeggs <bskeggs@...hat.com>,
        dri-devel@...ts.freedesktop.org, nouveau@...ts.freedesktop.org,
        stable@...r.kernel.org
Subject: Re: [PATCH] drm/nouveau/disp: Support more modes by checking with
 lower bpc

On Fri, Mar 31, 2023 at 12:39 AM Karol Herbst <kherbst@...hat.com> wrote:
>
> This allows us to advertise more modes especially on HDR displays.
>
> Fixes using 4K@60 modes on my TV and main display both using a HDMI to DP
> adapter. Also fixes similiar issues for users running into this.
>
> Cc: stable@...r.kernel.org # 5.10+
> Signed-off-by: Karol Herbst <kherbst@...hat.com>
> ---
>  drivers/gpu/drm/nouveau/dispnv50/disp.c | 32 +++++++++++++++++++++++++
>  drivers/gpu/drm/nouveau/nouveau_dp.c    |  8 ++++---
>  2 files changed, 37 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/nouveau/dispnv50/disp.c b/drivers/gpu/drm/nouveau/dispnv50/disp.c
> index ed9d374147b8d..f28e47c161dd9 100644
> --- a/drivers/gpu/drm/nouveau/dispnv50/disp.c
> +++ b/drivers/gpu/drm/nouveau/dispnv50/disp.c
> @@ -363,6 +363,35 @@ nv50_outp_atomic_check_view(struct drm_encoder *encoder,
>         return 0;
>  }
>
> +static void
> +nv50_outp_atomic_fix_depth(struct drm_encoder *encoder, struct drm_crtc_state *crtc_state)
> +{
> +       struct nv50_head_atom *asyh = nv50_head_atom(crtc_state);
> +       struct nouveau_encoder *nv_encoder = nouveau_encoder(encoder);
> +       struct drm_display_mode *mode = &asyh->state.adjusted_mode;
> +       unsigned int max_rate, mode_rate;
> +
> +       switch (nv_encoder->dcb->type) {
> +       case DCB_OUTPUT_DP:
> +               max_rate = nv_encoder->dp.link_nr * nv_encoder->dp.link_bw;
> +
> +                /* we don't support more than 10 anyway */
> +               asyh->or.bpc = max_t(u8, asyh->or.bpc, 10);

luckily I didn't push yet, but this has to be `min_t` :)

> +
> +               /* reduce the bpc until it works out */
> +               while (asyh->or.bpc > 6) {
> +                       mode_rate = DIV_ROUND_UP(mode->clock * asyh->or.bpc * 3, 8);
> +                       if (mode_rate <= max_rate)
> +                               break;
> +
> +                       asyh->or.bpc -= 2;
> +               }
> +               break;
> +       default:
> +               break;
> +       }
> +}
> +
>  static int
>  nv50_outp_atomic_check(struct drm_encoder *encoder,
>                        struct drm_crtc_state *crtc_state,
> @@ -381,6 +410,9 @@ nv50_outp_atomic_check(struct drm_encoder *encoder,
>         if (crtc_state->mode_changed || crtc_state->connectors_changed)
>                 asyh->or.bpc = connector->display_info.bpc;
>
> +       /* We might have to reduce the bpc */
> +       nv50_outp_atomic_fix_depth(encoder, crtc_state);
> +
>         return 0;
>  }
>
> diff --git a/drivers/gpu/drm/nouveau/nouveau_dp.c b/drivers/gpu/drm/nouveau/nouveau_dp.c
> index e00876f92aeea..d49b4875fc3c9 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_dp.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_dp.c
> @@ -263,8 +263,6 @@ nouveau_dp_irq(struct work_struct *work)
>  }
>
>  /* TODO:
> - * - Use the minimum possible BPC here, once we add support for the max bpc
> - *   property.
>   * - Validate against the DP caps advertised by the GPU (we don't check these
>   *   yet)
>   */
> @@ -276,7 +274,11 @@ nv50_dp_mode_valid(struct drm_connector *connector,
>  {
>         const unsigned int min_clock = 25000;
>         unsigned int max_rate, mode_rate, ds_max_dotclock, clock = mode->clock;
> -       const u8 bpp = connector->display_info.bpc * 3;
> +       /* Check with the minmum bpc always, so we can advertise better modes.
> +        * In particlar not doing this causes modes to be dropped on HDR
> +        * displays as we might check with a bpc of 16 even.
> +        */
> +       const u8 bpp = 6 * 3;
>
>         if (mode->flags & DRM_MODE_FLAG_INTERLACE && !outp->caps.dp_interlace)
>                 return MODE_NO_INTERLACE;
> --
> 2.39.2
>