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Commit 016ea687 authored by Joerg Roedel's avatar Joerg Roedel
Browse files

dma-debug: add documentation for the driver filter 



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

Signed-off-by: default avatarJoerg Roedel <joerg.roedel@amd.com>
parent 1745de5e

Documentation/DMA-API.txt

+12 −0
Original line number Diff line number Diff line
@@ -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