[PATCH] drm/ast: Fix modeset failed on DisplayPort

[Jammy Huang]

If we switch display and update cursor together, it could lead to
modeset failed because of concurrent access to IO registers.

Add lock protection in DP's edid access to avoid this problem.

Signed-off-by: Jammy Huang <jammy_huang at aspeedtech.com>
---
 drivers/gpu/drm/ast/ast_mode.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/gpu/drm/ast/ast_mode.c b/drivers/gpu/drm/ast/ast_mode.c
index 984ec590a7e7..fe5f1fd61361 100644
--- a/drivers/gpu/drm/ast/ast_mode.c
+++ b/drivers/gpu/drm/ast/ast_mode.c
@@ -1635,6 +1635,8 @@ static int ast_dp501_output_init(struct ast_private *ast)
 static int ast_astdp_connector_helper_get_modes(struct drm_connector *connector)
 {
 	void *edid;
+	struct drm_device *dev = connector->dev;
+	struct ast_private *ast = to_ast_private(dev);
 
 	int succ;
 	int count;
@@ -1643,10 +1645,18 @@ static int ast_astdp_connector_helper_get_modes(struct drm_connector *connector)
 	if (!edid)
 		goto err_drm_connector_update_edid_property;
 
+	/*
+	 * Protect access to I/O registers from concurrent modesetting
+	 * by acquiring the I/O-register lock.
+	 */
+	mutex_lock(&ast->ioregs_lock);
+
 	succ = ast_astdp_read_edid(connector->dev, edid);
 	if (succ < 0)
 		goto err_kfree;
 
+	mutex_unlock(&ast->ioregs_lock);
+
 	drm_connector_update_edid_property(connector, edid);
 	count = drm_add_edid_modes(connector, edid);
 	kfree(edid);
@@ -1654,6 +1664,7 @@ static int ast_astdp_connector_helper_get_modes(struct drm_connector *connector)
 	return count;
 
 err_kfree:
+	mutex_unlock(&ast->ioregs_lock);
 	kfree(edid);
 err_drm_connector_update_edid_property:
 	drm_connector_update_edid_property(connector, NULL);

base-commit: 61d325dcbc05d8fef88110d35ef7776f3ac3f68b
-- 
2.25.1