Add some documentation for the pxad_param structure, and describe the
contract behind the minimal required priority of a DMA channel.

Signed-off-by: Robert Jarzmik <robert.jarz...@free.fr>
---
 include/linux/dma/pxa-dma.h | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/include/linux/dma/pxa-dma.h b/include/linux/dma/pxa-dma.h
index e56ec7af4fd7..9fc594f69eff 100644
--- a/include/linux/dma/pxa-dma.h
+++ b/include/linux/dma/pxa-dma.h
@@ -9,6 +9,15 @@ enum pxad_chan_prio {
        PXAD_PRIO_LOWEST,
 };
 
+/**
+ * struct pxad_param - dma channel request parameters
+ * @drcmr: requestor line number
+ * @prio: minimal mandatory priority of the channel
+ *
+ * If a requested channel is granted, its priority will be at least @prio,
+ * ie. if PXAD_PRIO_LOW is required, the requested channel will be either
+ * PXAD_PRIO_LOW, PXAD_PRIO_NORMAL or PXAD_PRIO_HIGHEST.
+ */
 struct pxad_param {
        unsigned int drcmr;
        enum pxad_chan_prio prio;
-- 
2.11.0

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