[PATCH AUTOSEL 6.3 13/30] drm/ast: Fix modeset failed on DisplayPort

[Sasha Levin]

From: Jammy Huang <jammy_huang at aspeedtech.com>

[ Upstream commit 3692ababa322b4d9ffbd973865bc88018e896fcd ]

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.

Reviewed-by: Thomas Zimmermann <tzimmermann at suse.de>
Signed-off-by: Jammy Huang <jammy_huang at aspeedtech.com>
Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20230601004847.1115-1-jammy_huang@aspeedtech.com
Signed-off-by: Sasha Levin <sashal at kernel.org>
---
 drivers/gpu/drm/ast/ast_mode.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/ast/ast_mode.c b/drivers/gpu/drm/ast/ast_mode.c
index 984ec590a7e7d..e267cf9f505b9 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_device *ast = to_ast_device(dev);
 
 	int succ;
 	int count;
@@ -1643,9 +1645,17 @@ 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;
+		goto err_mutex_unlock;
+
+	mutex_unlock(&ast->ioregs_lock);
 
 	drm_connector_update_edid_property(connector, edid);
 	count = drm_add_edid_modes(connector, edid);
@@ -1653,7 +1663,8 @@ static int ast_astdp_connector_helper_get_modes(struct drm_connector *connector)
 
 	return count;
 
-err_kfree:
+err_mutex_unlock:
+	mutex_unlock(&ast->ioregs_lock);
 	kfree(edid);
 err_drm_connector_update_edid_property:
 	drm_connector_update_edid_property(connector, NULL);
-- 
2.39.2