Re: [PATCH v7 01/10] ARM: davinci: move private EDMA API to arm/common

[Sergei Shtylyov]

Hello.

On 02-02-2013 1:30, Russell King - ARM Linux wrote:

> > On Fri, Feb 01, 2013 at 11:49:11PM +0300, Sergei Shtylyov wrote:
> > > > good point, do you wanna send some patches ?

> > >     I have already sent them countless times and even stuck CPPI 4.1 support (in
> > > arch/arm/common/cppi41.c) in Russell's patch system. TI requested to remove the
> > > patch. :-(

> > sticking into arch/arm/common/ wasn't a nice move. But then again, so
> > wasn't asking for the patch to be removed :-s

> Err, patches don't get removed, they get moved to 'discarded'.

   Any chance to bring it back to life? :-)
   Although... drivers/usb/musb/cppi41.c would need to be somewhat reworked 
for at least AM35x and I don't have time. But that may change, of course.

> > > > I guess to make the MUSB side simpler we would need musb-dma-engine glue
> > > > to map dmaengine to the private MUSB API. Then we would have some
> > > > starting point to also move inventra (and anybody else) to dmaengine
> > > > API.

> > >     Why? Inventra is a dedicated device's private DMA controller, why make
> > > universal DMA driver for it?

> > because it doesn't make sense to support multiple DMA APIs. We can check
> > from MUSB's registers if it was configured with Inventra DMA support and
> > based on that we can register MUSB's own DMA Engine to dmaengine API.

> Hang on.  This is one of the DMA implementations which is closely
> coupled with the USB and only the USB?  If it is...

> I thought this had been discussed _extensively_ before.  I thought the
> resolution on it was:
> 1. It would not use the DMA engine API.
> 2. It would not live in arch/arm.
> 3. It would be placed nearby the USB driver it's associated with.

> (1) because we don't use APIs just for the hell of it - think.  Do we
> use the DMA engine API for PCI bus mastering ethernet controllers?  No.
> Do we use it for PCI bus mastering SCSI controllers?  No.  Because the
> DMA is integral to the rest of the device.

> The DMA engine API only makes sense if the DMA engine is a shared
> system resource.

   Thanks for such extensive wording in the support of my point. :-)

WBR, Sergei


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