[PATCH v2] drm/mediatek: Fix missing configuration flags in mtk_crtc_ddp_config()

[Chun-Kuang Hu]

Hi, Jason:

Jason-JH.Lin via B4 Relay
<devnull+jason-jh.lin.mediatek.com at kernel.org> 於 2024年8月19日 週一
下午11:26寫道：
>
> From: "Jason-JH.Lin" <jason-jh.lin at mediatek.com>
>
> In mtk_crtc_ddp_config(), mtk_crtc will use some configuration flags to
> generate instructions to cmdq_handle, such as:
>   state->pending_config
>   mtk_crtc->pending_planes
>   plane_state->pending.config
>   mtk_crtc->pending_async_planes
>   plane_state->pending.async_config
>
> These configuration flags may be set to false when a GCE IRQ comes calling
> ddp_cmdq_cb(). This may result in missing prepare instructions,
> especially if mtk_crtc_update_config() with the flase need_vblank (no need
> to wait for vblank) cases.
>
> Therefore, the mtk_crtc->config_updating flag is set at the beginning of
> mtk_crtc_update_config() to ensure that these configuration flags won't be
> changed when the mtk_crtc_ddp_config() is preparing instructions.
> But somehow the ddp_cmdq_cb() didn't use the mtk_crtc->config_updating
> flag to prevent those pending config flags from being cleared.
>
> To avoid missing the configuration when generating the config instruction,
> the config_updating flag should be added into ddp_cmdq_cb() and be
> protected with spin_lock.

Applied to mediatek-drm-next [1], thanks.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/chunkuang.hu/linux.git/log/?h=mediatek-drm-next

Regards,
Chun-Kuang.

>
> Fixes: 7f82d9c43879 ("drm/mediatek: Clear pending flag when cmdq packet is done")
> Signed-off-by: Jason-JH.Lin <jason-jh.lin at mediatek.com>
> ---
> Change in v2:
> Add spin_lock protection for config_updating flag.
> ---
>  drivers/gpu/drm/mediatek/mtk_crtc.c | 24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)
>
> diff --git a/drivers/gpu/drm/mediatek/mtk_crtc.c b/drivers/gpu/drm/mediatek/mtk_crtc.c
> index 6f34f573e127..b752c0b46383 100644
> --- a/drivers/gpu/drm/mediatek/mtk_crtc.c
> +++ b/drivers/gpu/drm/mediatek/mtk_crtc.c
> @@ -69,6 +69,8 @@ struct mtk_crtc {
>         /* lock for display hardware access */
>         struct mutex                    hw_lock;
>         bool                            config_updating;
> +       /* lock for config_updating to cmd buffer */
> +       spinlock_t                      config_lock;
>  };
>
>  struct mtk_crtc_state {
> @@ -107,10 +109,13 @@ static void mtk_crtc_finish_page_flip(struct mtk_crtc *mtk_crtc)
>  static void mtk_drm_finish_page_flip(struct mtk_crtc *mtk_crtc)
>  {
>         drm_crtc_handle_vblank(&mtk_crtc->base);
> +
> +       spin_lock(&mtk_crtc->config_lock);
>         if (!mtk_crtc->config_updating && mtk_crtc->pending_needs_vblank) {
>                 mtk_crtc_finish_page_flip(mtk_crtc);
>                 mtk_crtc->pending_needs_vblank = false;
>         }
> +       spin_unlock(&mtk_crtc->config_lock);
>  }
>
>  #if IS_REACHABLE(CONFIG_MTK_CMDQ)
> @@ -314,6 +319,13 @@ static void ddp_cmdq_cb(struct mbox_client *cl, void *mssg)
>
>         state = to_mtk_crtc_state(mtk_crtc->base.state);
>
> +       spin_lock(&mtk_crtc->config_lock);
> +
> +       if (mtk_crtc->config_updating) {
> +               spin_unlock(&mtk_crtc->config_lock);
> +               goto ddp_cmdq_cb_out;
> +       }
> +
>         state->pending_config = false;
>
>         if (mtk_crtc->pending_planes) {
> @@ -340,6 +352,10 @@ static void ddp_cmdq_cb(struct mbox_client *cl, void *mssg)
>                 mtk_crtc->pending_async_planes = false;
>         }
>
> +       spin_unlock(&mtk_crtc->config_lock);
> +
> +ddp_cmdq_cb_out:
> +
>         mtk_crtc->cmdq_vblank_cnt = 0;
>         wake_up(&mtk_crtc->cb_blocking_queue);
>  }
> @@ -571,7 +587,11 @@ static void mtk_crtc_update_config(struct mtk_crtc *mtk_crtc, bool needs_vblank)
>         int i;
>
>         mutex_lock(&mtk_crtc->hw_lock);
> +
> +       spin_lock(&mtk_crtc->config_lock);
>         mtk_crtc->config_updating = true;
> +       spin_unlock(&mtk_crtc->config_lock);
> +
>         if (needs_vblank)
>                 mtk_crtc->pending_needs_vblank = true;
>
> @@ -625,7 +645,10 @@ static void mtk_crtc_update_config(struct mtk_crtc *mtk_crtc, bool needs_vblank)
>                 mbox_client_txdone(mtk_crtc->cmdq_client.chan, 0);
>         }
>  #endif
> +       spin_lock(&mtk_crtc->config_lock);
>         mtk_crtc->config_updating = false;
> +       spin_unlock(&mtk_crtc->config_lock);
> +
>         mutex_unlock(&mtk_crtc->hw_lock);
>  }
>
> @@ -1068,6 +1091,7 @@ int mtk_crtc_create(struct drm_device *drm_dev, const unsigned int *path,
>                 drm_mode_crtc_set_gamma_size(&mtk_crtc->base, gamma_lut_size);
>         drm_crtc_enable_color_mgmt(&mtk_crtc->base, 0, has_ctm, gamma_lut_size);
>         mutex_init(&mtk_crtc->hw_lock);
> +       spin_lock_init(&mtk_crtc->config_lock);
>
>  #if IS_REACHABLE(CONFIG_MTK_CMDQ)
>         i = priv->mbox_index++;
>
> ---
> base-commit: 469f1bad3c1c6e268059f78c0eec7e9552b3894c
> change-id: 20240819-drm-fixup-0819-f51e2d37fcd7
>
> Best regards,
> --
> Jason-JH.Lin <jason-jh.lin at mediatek.com>
>
>