On Tue, May 02, 2017 at 02:03:06PM +0200, Arnd Bergmann wrote: > On Tue, May 2, 2017 at 1:15 PM, Simon Horman <horms+renesas@xxxxxxxxxxxx> wrote: > > Hi Wolfram, Hi Arnd, Hi all, > > > > the intention of this patch-set is to refactor the DMA support in > > the Renesas SDHI driver in order to make it easier to add support > > for using the SDHI hardware with different DMA implementations. > > > > This is based on earlier work, posted as "[PATCH/RFC v3 0/6] mmc: > > renesas_sdhi: add R-Car Gen-3 DMA support". It attempts to implement > > the reworking of the driver proposed by Arnd[1] in his review of that > > patch-set. > > > > [1] http://www.spinics.net/lists/linux-mmc/msg38004.html > > > > Unlike that patch-set this patch-set does not add support for > > R-Car Gen-3 DMA. Rather it focuses on refactoring the code. > > Looks fine overall. Remind me why we are not using the dma-engine > framework though. IIRC this is because at least one of the possible > DMA implementations is tightly integrated with the TMIO register > set and not easily split out into another driver, right? In a nutshell, yes, that is my understanding. The DMA implementation that is currently present in mainline uses the SYS-DMAC device and the DMA Engine framework is used. However, we expect to support devices that make use of built-in bus master engine for SDHI DMA. In this case it does not seem to make much sense to break out DMA support into a separate driver as it can only be used as part of SDHI which it is a part of. This is as opposed to SYS-DMAC where the SYS-DMAC device may be used by several different devices, f.e. SDHI and SCIF (serial).
