gpu: host1x: Add locking in channel allocation

Add locking around channel allocation to avoid race conditions.

Signed-off-by: Mikko Perttunen <mperttunen@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230901111510.663401-1-cyndis@kapsi.fi

drivers/gpu/host1x/channel.c

@@ -27,6 +27,8 @@ int host1x_channel_list_init(struct host1x_channel_list *chlist,
 		return -ENOMEM;
 	}
 
+	mutex_init(&chlist->lock);
+
 	return 0;
 }
 
@@ -104,8 +106,11 @@ static struct host1x_channel *acquire_unused_channel(struct host1x *host)
 	unsigned int max_channels = host->info->nb_channels;
 	unsigned int index;
 
+	mutex_lock(&chlist->lock);
+
 	index = find_first_zero_bit(chlist->allocated_channels, max_channels);
 	if (index >= max_channels) {
+		mutex_unlock(&chlist->lock);
 		dev_err(host->dev, "failed to find free channel\n");
 		return NULL;
 	}
@@ -114,6 +119,8 @@ static struct host1x_channel *acquire_unused_channel(struct host1x *host)
 
 	set_bit(index, chlist->allocated_channels);
 
+	mutex_unlock(&chlist->lock);
+
 	return &chlist->channels[index];
 }
 

drivers/gpu/host1x/channel.h

@@ -10,6 +10,7 @@
 
 #include <linux/io.h>
 #include <linux/kref.h>
+#include <linux/mutex.h>
 
 #include "cdma.h"
 
@@ -18,6 +19,8 @@ struct host1x_channel;
 
 struct host1x_channel_list {
 	struct host1x_channel *channels;
+
+	struct mutex lock;
 	unsigned long *allocated_channels;
 };