Re: Depreciated spi_master.transfer and "prepared spi messages" for an optimized pipelined-SPI-DMA-driver

[Mark Brown <broonie-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>]

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On Sat, Nov 09, 2013 at 06:30:56PM +0000, Mark Brown wrote:

> You've been doing a bunch of other performance improvements as well,
> it's not clear to me how much of this is coming from the API change and
> how much of this is due to changes which can also be done by improving
> the implementation and without requiring drivers to be specifically
> updated to take advantage of it. 

An example of the sort of thing I'm concerned about: if I understand
correctly one of the things the prepare and unprepare operations in the
driver do is the DMA mapping.  This will mean that if you prepare in the
caller the system will be able to do the DMA mapping while a prior
transfer is in progress which should help performance.  That's a good
thing to do but it should be something that can be done as part of the
existing API without needing drivers using SPI to be updated.

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