powerpc: document the "fsl,ssi-dma-channel" compatible property

The "fsl,ssi-dma-channel" compatible property is used to specify a DMA channel
on the Freescale Elo DMA controller that should be used exclusively by the
Freescale SSI audio controller.  When a property is marked as such, the Elo
DMA driver will ignore it, and so it will be available for the sound drivers.

Signed-off-by: Timur Tabi <timur@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>

1 files changed, 11 insertions, 2 deletions

diff --git a/Documentation/powerpc/dts-bindings/fsl/dma.txt b/Documentation/powerpc/dts-bindings/fsl/dma.txt
index 86826df00e64..cc453110fc46 100644
--- a/Documentation/powerpc/dts-bindings/fsl/dma.txt
+++ b/Documentation/powerpc/dts-bindings/fsl/dma.txt
@@ -20,7 +20,7 @@ Required properties:
         - compatible        : compatible list, contains 2 entries, first is
                          "fsl,CHIP-dma-channel", where CHIP is the processor
                          (mpc8349, mpc8350, etc.) and the second is
-                         "fsl,elo-dma-channel"
+                         "fsl,elo-dma-channel". However, see note below.
         - reg               : <registers mapping for channel>
         - cell-index        : dma channel index starts at 0.
 
@@ -82,7 +82,7 @@ Required properties:
         - compatible        : compatible list, contains 2 entries, first is
                          "fsl,CHIP-dma-channel", where CHIP is the processor
                          (mpc8540, mpc8560, etc.) and the second is
-                         "fsl,eloplus-dma-channel"
+                         "fsl,eloplus-dma-channel". However, see note below.
         - cell-index        : dma channel index starts at 0.
         - reg               : <registers mapping for channel>
         - interrupts        : <interrupt mapping for DMA channel IRQ>
@@ -125,3 +125,12 @@ Example:
                         interrupts = <17 2>;
                 };
         };
+
+Note on DMA channel compatible properties: The compatible property must say
+"fsl,elo-dma-channel" or "fsl,eloplus-dma-channel" to be used by the Elo DMA
+driver (fsldma).  Any DMA channel used by fsldma cannot be used by another
+DMA driver, such as the SSI sound drivers for the MPC8610.  Therefore, any DMA
+channel that should be used for another driver should not use
+"fsl,elo-dma-channel" or "fsl,eloplus-dma-channel".  For the SSI drivers, for
+example, the compatible property should be "fsl,ssi-dma-channel".  See ssi.txt
+for more information.