Hannes reported a problem with setting up dma transfers on a mcb device.
The problem boiled down to the use of a wrong 'device' for the dma
functions.
Document how to setup dma transfers for a IP core on a mcb carrier.
Reported-by: Hannes Duerr <Hannes.Duerr@xxxxxxxxxx>
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@xxxxxxx>
---
Documentation/driver-api/men-chameleon-bus.rst | 12 ++++++++++++
1 file changed, 12 insertions(+)
diff --git a/Documentation/driver-api/men-chameleon-bus.rst b/Documentation/driver-api/men-chameleon-bus.rst
index 1b1f048aa748..6f0b9ee47595 100644
--- a/Documentation/driver-api/men-chameleon-bus.rst
+++ b/Documentation/driver-api/men-chameleon-bus.rst
@@ -18,6 +18,7 @@ MEN Chameleon Bus
4.1 The driver structure
4.2 Probing and attaching
4.3 Initializing the driver
+ 4.4 Using DMA
Introduction
@@ -173,3 +174,14 @@ module at the MCB core::
The module_mcb_driver() macro can be used to reduce the above code::
module_mcb_driver(foo_driver);
+
+Using DMA
+---------
+
+To make use of the kernel's DMA-API's function, you will need to use the
+carrier device's 'struct device'. Fortunately 'struct mcb_device' embeds a
+pointer (->dma_dev) to the carrier's device for DMA purposes::
+
+ ret = dma_set_mask_and_coherent(&mdev->dma_dev, DMA_BIT_MASK(dma_bits));
+ if (rc)
+ /* Handle errors */
--
2.26.2
