[PATCH v4 10/12] drm/ast: Acquire I/O-register lock in DDC code

[Thomas Zimmermann <tzimmermann@suse.de>]

The modeset lock protects the DDC code from concurrent modeset
operations, which use the same registers. Move that code from the
connector helpers into the DDC helpers .pre_xfer() and .post_xfer().

Both, .pre_xfer() and .post_xfer(), enclose the transfer of data blocks
over the I2C channel in the internal I2C function bit_xfer(). Both
calls are executed unconditionally if present. Invoking DDC transfers
from any where within the driver now takes the lock.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
---
 drivers/gpu/drm/ast/ast_ddc.c  | 24 ++++++++++++++++++++++++
 drivers/gpu/drm/ast/ast_mode.c | 30 ++++--------------------------
 2 files changed, 28 insertions(+), 26 deletions(-)

diff --git a/drivers/gpu/drm/ast/ast_ddc.c b/drivers/gpu/drm/ast/ast_ddc.c
index b84e656124f18..b7718084422f3 100644
--- a/drivers/gpu/drm/ast/ast_ddc.c
+++ b/drivers/gpu/drm/ast/ast_ddc.c
@@ -59,6 +59,28 @@ static void ast_ddc_algo_bit_data_setscl(void *data, int state)
 	}
 }
 
+static int ast_ddc_algo_bit_data_pre_xfer(struct i2c_adapter *adapter)
+{
+	struct ast_ddc *ddc = i2c_get_adapdata(adapter);
+	struct ast_device *ast = ddc->ast;
+
+	/*
+	 * Protect access to I/O registers from concurrent modesetting
+	 * by acquiring the I/O-register lock.
+	 */
+	mutex_lock(&ast->modeset_lock);
+
+	return 0;
+}
+
+static void ast_ddc_algo_bit_data_post_xfer(struct i2c_adapter *adapter)
+{
+	struct ast_ddc *ddc = i2c_get_adapdata(adapter);
+	struct ast_device *ast = ddc->ast;
+
+	mutex_unlock(&ast->modeset_lock);
+}
+
 static int ast_ddc_algo_bit_data_getsda(void *data)
 {
 	struct ast_ddc *ddc = data;
@@ -137,6 +159,8 @@ struct ast_ddc *ast_ddc_create(struct ast_device *ast)
 	bit->setscl = ast_ddc_algo_bit_data_setscl;
 	bit->getsda = ast_ddc_algo_bit_data_getsda;
 	bit->getscl = ast_ddc_algo_bit_data_getscl;
+	bit->pre_xfer = ast_ddc_algo_bit_data_pre_xfer;
+	bit->post_xfer = ast_ddc_algo_bit_data_post_xfer;
 
 	adapter->algo_data = bit;
 	ret = i2c_bit_add_bus(adapter);
diff --git a/drivers/gpu/drm/ast/ast_mode.c b/drivers/gpu/drm/ast/ast_mode.c
index fc73d3b65b2a1..8766a0f2eb3c7 100644
--- a/drivers/gpu/drm/ast/ast_mode.c
+++ b/drivers/gpu/drm/ast/ast_mode.c
@@ -1346,30 +1346,19 @@ static int ast_crtc_init(struct drm_device *dev)
 
 static int ast_vga_connector_helper_get_modes(struct drm_connector *connector)
 {
-	struct drm_device *dev = connector->dev;
-	struct ast_device *ast = to_ast_device(dev);
 	struct edid *edid;
 	int count;
 
-	/*
-	 * Protect access to I/O registers from concurrent modesetting
-	 * by acquiring the I/O-register lock.
-	 */
-	mutex_lock(&ast->modeset_lock);
-
 	edid = drm_get_edid(connector, connector->ddc);
 	if (!edid)
-		goto err_mutex_unlock;
-
-	mutex_unlock(&ast->modeset_lock);
+		goto err_drm_get_edid;
 
 	count = drm_add_edid_modes(connector, edid);
 	kfree(edid);
 
 	return count;
 
-err_mutex_unlock:
-	mutex_unlock(&ast->modeset_lock);
+err_drm_get_edid:
 	drm_connector_update_edid_property(connector, NULL);
 	return 0;
 }
@@ -1444,30 +1433,19 @@ static int ast_vga_output_init(struct ast_device *ast)
 
 static int ast_sil164_connector_helper_get_modes(struct drm_connector *connector)
 {
-	struct drm_device *dev = connector->dev;
-	struct ast_device *ast = to_ast_device(dev);
 	struct edid *edid;
 	int count;
 
-	/*
-	 * Protect access to I/O registers from concurrent modesetting
-	 * by acquiring the I/O-register lock.
-	 */
-	mutex_lock(&ast->modeset_lock);
-
 	edid = drm_get_edid(connector, connector->ddc);
 	if (!edid)
-		goto err_mutex_unlock;
-
-	mutex_unlock(&ast->modeset_lock);
+		goto err_drm_get_edid;
 
 	count = drm_add_edid_modes(connector, edid);
 	kfree(edid);
 
 	return count;
 
-err_mutex_unlock:
-	mutex_unlock(&ast->modeset_lock);
+err_drm_get_edid:
 	drm_connector_update_edid_property(connector, NULL);
 	return 0;
 }
-- 
2.44.0