[PATCH v3 3/6] spi: davinci: use rx buffer as dummy tx buffer

[Mark Brown]

On Thu, Feb 23, 2017 at 07:01:58PM +0100, Frode Isaksen wrote:
> When doing rx-only transfer, the transfer will fail
> if the number of SG entries exceeds 20.
> This happens because the eDMA DMA engine is limited
> to 20 SG entries in one transaction, and when the
> DMA transcation is resumed (which takes > 150us),
> rx errors occurs because the slave is still transmitting.
> Fix this by using the rx buffer as the dummy tx buffer,
> so that resuming the rx transcation happens at the same
> time as resuming the tx transcation.

Please submit a followup patch adding a comment explaing what's going
in the actual code as someone's going to clean this up at some point.
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