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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>
This commit is contained in:
Joerg Roedel 2009-05-22 21:57:23 +02:00
parent 1745de5e56
commit 016ea6874a
1 changed files with 12 additions and 0 deletions
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12
Documentation/DMA-API.txt
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@ -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