[PATCH v2 3/3] drm/vc4: dsi: Serialize host transfers

[Henry Zhang <henryzhang62@gmail.com>]

vc4_dsi_host_transfer() fills the command FIFOs and the TXPKT registers
and waits on a single completion without any locking. Two callers
sending at the same time, for example a panel driver and a backlight
update, can overwrite each other's packets, and the timeout recovery
added in the previous patch could reset the block under a transfer
that is still in flight.

Hold a mutex for the whole host transfer, including the recovery.

Signed-off-by: Henry Zhang <henryzhang62@gmail.com>
---

Notes:
    New in v2 (Sashiko review).

 drivers/gpu/drm/vc4/vc4_dsi.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/gpu/drm/vc4/vc4_dsi.c b/drivers/gpu/drm/vc4/vc4_dsi.c
index 2d985bc..627adf0 100644
--- a/drivers/gpu/drm/vc4/vc4_dsi.c
+++ b/drivers/gpu/drm/vc4/vc4_dsi.c
@@ -25,6 +25,7 @@
 #include <linux/dma-mapping.h>
 #include <linux/dmaengine.h>
 #include <linux/io.h>
+#include <linux/mutex.h>
 #include <linux/of.h>
 #include <linux/of_address.h>
 #include <linux/platform_device.h>
@@ -595,6 +596,8 @@ struct vc4_dsi {
 	 */
 	struct clk *pixel_clock;
 
+	/* Serializes host transfers, including the recovery after a timeout. */
+	struct mutex transfer_lock;
 	struct completion xfer_completion;
 	int xfer_result;
 	int irq;
@@ -1434,6 +1437,8 @@ static ssize_t vc4_dsi_host_transfer(struct mipi_dsi_host *host,
 	u32 disp0_ctrl;
 	ssize_t ret;
 
+	guard(mutex)(&dsi->transfer_lock);
+
 	ret = vc4_dsi_transfer(dsi, msg);
 	if (ret != -ETIMEDOUT)
 		return ret;
@@ -1911,6 +1916,7 @@ static int vc4_dsi_dev_probe(struct platform_device *pdev)
 {
 	struct device *dev = &pdev->dev;
 	struct vc4_dsi *dsi;
+	int ret;
 
 	dsi = devm_drm_bridge_alloc(&pdev->dev, struct vc4_dsi, bridge, &vc4_dsi_bridge_funcs);
 	if (IS_ERR(dsi))
@@ -1918,6 +1924,9 @@ static int vc4_dsi_dev_probe(struct platform_device *pdev)
 	dev_set_drvdata(dev, dsi);
 
 	dsi->pdev = pdev;
+	ret = devm_mutex_init(dev, &dsi->transfer_lock);
+	if (ret)
+		return ret;
 #ifdef CONFIG_OF
 	dsi->bridge.of_node = dev->of_node;
 #endif
-- 
2.47.3