dma-debug: add documentation for the driver filter

This patch adds the driver filter feature to the dma-debug
documentation.

Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>

1 files changed, 12 insertions, 0 deletions

diff --git a/Documentation/DMA-API.txt b/Documentation/DMA-API.txt
index d9aa43d78bcc..25fb8bcf32a2 100644
--- a/Documentation/DMA-API.txt
+++ b/Documentation/DMA-API.txt
@@ -704,12 +704,24 @@ this directory the following files can currently be found:
                                 The current number of free dma_debug_entries
                                 in the allocator.
 
+        dma-api/driver-filter
+                                You can write a name of a driver into this file
+                                to limit the debug output to requests from that
+                                particular driver. Write an empty string to
+                                that file to disable the filter and see
+                                all errors again.
+
 If you have this code compiled into your kernel it will be enabled by default.
 If you want to boot without the bookkeeping anyway you can provide
 'dma_debug=off' as a boot parameter. This will disable DMA-API debugging.
 Notice that you can not enable it again at runtime. You have to reboot to do
 so.
 
+If you want to see debug messages only for a special device driver you can
+specify the dma_debug_driver=<drivername> parameter. This will enable the
+driver filter at boot time. The debug code will only print errors for that
+driver afterwards. This filter can be disabled or changed later using debugfs.
+
 When the code disables itself at runtime this is most likely because it ran
 out of dma_debug_entries. These entries are preallocated at boot. The number
 of preallocated entries is defined per architecture. If it is too low for you