media: vivid: add cache_hints module param

Add a cache_hints module param to control per-queue user space cache
hints support.
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

Documentation/admin-guide/media/vivid.rst

@@ -293,6 +293,15 @@ all configurable using the following module options:
 		- 0: vmalloc
 		- 1: dma-contig
 
+- cache_hints:
+
+	specifies if the device should set queues' user-space cache and memory
+	consistency hint capability (V4L2_BUF_CAP_SUPPORTS_MMAP_CACHE_HINTS).
+	The hints are valid only when using MMAP streaming I/O. Default is 0.
+
+		- 0: forbid hints
+		- 1: allow hints
+
 Taken together, all these module options allow you to precisely customize
 the driver behavior and test your application with all sorts of permutations.
 It is also very suitable to emulate hardware that is not yet available, e.g.

drivers/media/test-drivers/vivid/vivid-core.c

@@ -169,6 +169,14 @@ MODULE_PARM_DESC(allocators, " memory allocator selection, default is 0.\n"
 			     "\t\t    0 == vmalloc\n"
 			     "\t\t    1 == dma-contig");
 
+static unsigned int cache_hints[VIVID_MAX_DEVS] = {
+	[0 ... (VIVID_MAX_DEVS - 1)] = 0
+};
+module_param_array(cache_hints, uint, NULL, 0444);
+MODULE_PARM_DESC(cache_hints, " user-space cache hints, default is 0.\n"
+			     "\t\t    0 == forbid\n"
+			     "\t\t    1 == allow");
+
 static struct vivid_dev *vivid_devs[VIVID_MAX_DEVS];
 
 const struct v4l2_rect vivid_min_rect = {
@@ -819,6 +827,7 @@ static int vivid_create_queue(struct vivid_dev *dev,
 	q->lock = &dev->mutex;
 	q->dev = dev->v4l2_dev.dev;
 	q->supports_requests = true;
+	q->allow_cache_hints = (cache_hints[dev->inst] == 1);
 
 	return vb2_queue_init(q);
 }