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Documentation: document dma device use for mcb

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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@duagon.com>
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Link: https://lore.kernel.org/r/3bdc8f76b30c2b0e2a2bfab06c2e73797ddc9384.1608305690.git.johannes.thumshirn@wdc.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
This commit is contained in:
Johannes Thumshirn 2020-12-19 00:35:25 +09:00 committed by Jonathan Corbet
parent 7178b4a7d6
commit 7594bb08fb
1 changed files with 12 additions and 0 deletions
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12
Documentation/driver-api/men-chameleon-bus.rst
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@ -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 */