On 01/09/2017 01:48 PM, Mark Brown wrote:
On Thu, Jan 05, 2017 at 09:26:17PM -0600, David Lechner wrote:
This allows SPI devices specified in a device tree to use DMA when the
master controller.
Since device tree is supposed to only describe the hardware, adding such
a configuration option to device tree would not be acceptable. So, this
is the best we can do for now to get SPI devices working with DMA.
Unfortunately, this excludes the possibility of using one SPI device with
DMA and one without on the same master.
Why would you ever want to do that? What would ever make sense about
not using DMA if it's available and the transfer is suitably large, or
conversely why would one want to force DMA even if PIO would be more
performant?
I don't particularly want to do that, but that is the way the
spi-davinci driver currently works. The choice between DMA or PIO is
specified in the platform data on a per-device basis.
What I get from your remarks is that this is wrong and it needs to be
fixed. If that is so, could someone please point out a driver that does
it the right way and I will try to fix it.
When I originally submitted this patch, there was some discussion as to whether
dspi->dma_rx should be changed to return an error rather than being null.
However, I prefer it the way it is and don't see a compelling reason to change
it.
I don't know what the above comment means, sorry (and don't recall
having seen any earlier versions of this).
FWIW, you can find the previous conversation at
https://patchwork.kernel.org/patch/9437901/
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