dma-buf: deprecate DMABUF_SYSFS_STATS

Add a warning that this UAPI wasn't such a good idea and shouldn't be
used by anybody.

That should give us a better chance to remove it at some point and
prevents others from running into the same issues.
Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: T.J. Mercier <tjmercier@google.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220617085702.4298-1-christian.koenig@amd.com

drivers/dma-buf/Kconfig

@@ -75,7 +75,7 @@ menuconfig DMABUF_HEAPS
 	  between drivers.
 
 menuconfig DMABUF_SYSFS_STATS
-	bool "DMA-BUF sysfs statistics"
+	bool "DMA-BUF sysfs statistics (DEPRECATED)"
 	depends on DMA_SHARED_BUFFER
 	help
 	   Choose this option to enable DMA-BUF sysfs statistics
@@ -85,6 +85,10 @@ menuconfig DMABUF_SYSFS_STATS
 	   statistics for the DMA-BUF with the unique inode number
 	   <inode_number>.
 
+	   This option is deprecated and should sooner or later be removed.
+	   Android is the only user of this and it turned out that this resulted
+	   in quite some performance problems.
+
 source "drivers/dma-buf/heaps/Kconfig"
 
 endmenu