linux-kernel - [PATCH v2] drm/mediatek: Fix missing configuration flags in mtk_crtc_ddp

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Message-Id: <20240819-drm-fixup-0819-v2-1-a03580ece3ec@mediatek.com>
Date: Mon, 19 Aug 2024 23:25:10 +0800
From: "Jason-JH.Lin via B4 Relay" <devnull+jason-jh.lin.mediatek.com@...nel.org>
To: Chun-Kuang Hu <chunkuang.hu@...nel.org>, 
 AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
Cc: Philipp Zabel <p.zabel@...gutronix.de>, 
 David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>, 
 Singo Chang <singo.chang@...iatek.com>, Nancy Lin <nancy.lin@...iatek.com>, 
 Project_Global_Chrome_Upstream_Group@...iatek.com, 
 dri-devel@...ts.freedesktop.org, linux-mediatek@...ts.infradead.org, 
 linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
 "Jason-JH.Lin" <jason-jh.lin@...iatek.com>
Subject: [PATCH v2] drm/mediatek: Fix missing configuration flags in
 mtk_crtc_ddp_config()

From: "Jason-JH.Lin" <jason-jh.lin@...iatek.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.

Fixes: 7f82d9c43879 ("drm/mediatek: Clear pending flag when cmdq packet is done")
Signed-off-by: Jason-JH.Lin <jason-jh.lin@...iatek.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@...iatek.com>