[PATCH v2] drm/mediatek: Add spinlock for setting vblank event in atomic_begin

[CK Hu (胡俊光)]

Hi, Jason:

On Wed, 2023-09-20 at 17:06 +0800, Jason-JH.Lin wrote:
> Add spinlock protection to avoid race condition on vblank event
> between mtk_drm_crtc_atomic_begin() and mtk_drm_finish_page_flip().

Reviewed-by: CK Hu <ck.hu at mediatek.com>

> 
> Fixes: 119f5173628a ("drm/mediatek: Add DRM Driver for Mediatek SoC
> MT8173.")
> Signed-off-by: Jason-JH.Lin <jason-jh.lin at mediatek.com>
> Suggested-by: AngeloGioacchino Del Regno <
> angelogioacchino.delregno at collabora.com>
> Reviewed-by: Alexandre Mergnat <amergnat at baylibre.com>
> Reviewed-by: Fei Shao <fshao at chromium.org>
> Tested-by: Fei Shao <fshao at chromium.org>
> ---
>  drivers/gpu/drm/mediatek/mtk_drm_crtc.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/gpu/drm/mediatek/mtk_drm_crtc.c
> b/drivers/gpu/drm/mediatek/mtk_drm_crtc.c
> index b6fa4ad2f94d..cab4fe092f13 100644
> --- a/drivers/gpu/drm/mediatek/mtk_drm_crtc.c
> +++ b/drivers/gpu/drm/mediatek/mtk_drm_crtc.c
> @@ -744,6 +744,7 @@ static void mtk_drm_crtc_atomic_begin(struct
> drm_crtc *crtc,
>  									
>   crtc);
>  	struct mtk_crtc_state *mtk_crtc_state =
> to_mtk_crtc_state(crtc_state);
>  	struct mtk_drm_crtc *mtk_crtc = to_mtk_crtc(crtc);
> +	unsigned long flags;
>  
>  	if (mtk_crtc->event && mtk_crtc_state->base.event)
>  		DRM_ERROR("new event while there is still a pending
> event\n");
> @@ -751,7 +752,11 @@ static void mtk_drm_crtc_atomic_begin(struct
> drm_crtc *crtc,
>  	if (mtk_crtc_state->base.event) {
>  		mtk_crtc_state->base.event->pipe =
> drm_crtc_index(crtc);
>  		WARN_ON(drm_crtc_vblank_get(crtc) != 0);
> +
> +		spin_lock_irqsave(&crtc->dev->event_lock, flags);
>  		mtk_crtc->event = mtk_crtc_state->base.event;
> +		spin_unlock_irqrestore(&crtc->dev->event_lock, flags);
> +
>  		mtk_crtc_state->base.event = NULL;
>  	}
>  }