linux-kernel - Re: Re: [PATCH] dmaengine: bcm2835: Add slave dma support

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Date:	Thu, 16 Apr 2015 21:06:49 +0200
From:	Alexander Stein <alexanders83@....de>
To:	linux-rpi-kernel@...ts.infradead.org
Cc:	Stefan Wahren <info@...egoodbye.de>,
	Noralf Trønnes <noralf@...nnes.org>,
	dmaengine@...r.kernel.org, vinod.koul@...el.com,
	dan.j.williams@...el.com, jonathan@...pberrypi.org,
	linux-kernel@...r.kernel.org
Subject: Re: Re: [PATCH] dmaengine: bcm2835: Add slave dma support

Hi Stefan,

On Wednesday 15 April 2015, 21:00:26 wrote Stefan Wahren:
> Am 15.04.2015 um 11:56 schrieb Noralf Trønnes:
> > Add slave transfer capability to BCM2835 dmaengine driver.
> > This patch is pulled from the bcm2708-dmaengine driver in the
> > Raspberry Pi repo. The work was done by Gellert Weisz.
> >
> > Tested with the bcm2835-mmc driver from the same repo.
> 
> why not with the upstream kernel?

I also looked at slave dma support, especially for use in mmc. It turns our that bcm2835-mmc is written more or less completly new.
Mainline linux uses sdhci "framework" which internally uses the SDMA and/or ADMA (both internal, to SD/MMC controller, DMA units) which can be supported by an SDHCI compatible controller.
AFAIK the SD/MMC controller in bcm2835 lacks both that is why the driver only uses PIO. I dunno if external DMA usage can so easily be integrated into the sdhci, I have my doubts.

Best regards,
Alexander

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