[PATCH v6 13/16] drm/bridge: synopsys: dw-dp: Protect sdp_reg_bank from concurrent access

[Sebastian Reichel]

Right now sdp_reg_bank is only used during atomic enable/disable and
thus there is no risk of two threads accidently claiming the same bit.

This changes once more SDP users (like audio support) are added, so
introduce a mutex to protect concurrent access to the bitmap.

Signed-off-by: Sebastian Reichel <sebastian.reichel@xxxxxxxxxxxxx>
---
 drivers/gpu/drm/bridge/synopsys/dw-dp.c | 24 +++++++++++++++++-------
 1 file changed, 17 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/bridge/synopsys/dw-dp.c b/drivers/gpu/drm/bridge/synopsys/dw-dp.c
index 1bbb39b8d0be..88b95938649a 100644
--- a/drivers/gpu/drm/bridge/synopsys/dw-dp.c
+++ b/drivers/gpu/drm/bridge/synopsys/dw-dp.c
@@ -322,6 +322,8 @@ struct dw_dp {
 	struct dw_dp_hotplug hotplug;
 	/* Serialize hpd status access */
 	struct mutex irq_lock;
+	/* Serialize sdp_reg_bank access */
+	struct mutex sdp_lock;
 
 	struct drm_dp_aux aux;
 
@@ -1045,11 +1047,13 @@ static int dw_dp_send_sdp(struct dw_dp *dp, struct dw_dp_sdp *sdp)
 	u32 reg;
 	int i, nr;
 
-	nr = find_first_zero_bit(dp->sdp_reg_bank, SDP_REG_BANK_SIZE);
-	if (nr < SDP_REG_BANK_SIZE)
-		set_bit(nr, dp->sdp_reg_bank);
-	else
-		return -EBUSY;
+	scoped_guard(mutex, &dp->sdp_lock) {
+		nr = find_first_zero_bit(dp->sdp_reg_bank, SDP_REG_BANK_SIZE);
+		if (nr < SDP_REG_BANK_SIZE)
+			set_bit(nr, dp->sdp_reg_bank);
+		else
+			return -EBUSY;
+	}
 
 	reg = DW_DP_SDP_REGISTER_BANK + nr * 9 * 4;
 
@@ -1683,7 +1687,8 @@ static void dw_dp_bridge_atomic_enable(struct drm_bridge *bridge,
 		return;
 	}
 
-	set_bit(0, dp->sdp_reg_bank);
+	scoped_guard(mutex, &dp->sdp_lock)
+		set_bit(0, dp->sdp_reg_bank);
 
 	ret = dw_dp_link_enable(dp);
 	if (ret < 0) {
@@ -1723,7 +1728,8 @@ static void dw_dp_bridge_atomic_disable(struct drm_bridge *bridge,
 
 	dw_dp_video_disable(dp);
 	dw_dp_link_disable(dp);
-	bitmap_zero(dp->sdp_reg_bank, SDP_REG_BANK_SIZE);
+	scoped_guard(mutex, &dp->sdp_lock)
+		bitmap_zero(dp->sdp_reg_bank, SDP_REG_BANK_SIZE);
 	dw_dp_reset(dp);
 	pm_runtime_put_autosuspend(dp->dev);
 }
@@ -2189,6 +2195,10 @@ struct dw_dp *dw_dp_probe(struct platform_device *pdev, const struct dw_dp_plat_
 	if (ret)
 		return ERR_PTR(ret);
 
+	ret = devm_mutex_init(dev, &dp->sdp_lock);
+	if (ret)
+		return ERR_PTR(ret);
+
 	res = devm_platform_ioremap_resource(pdev, 0);
 	if (IS_ERR(res))
 		return ERR_CAST(res);

-- 
2.53.0