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List:       linux-arm-kernel
Subject:    Re: PXA27x device driver example with DMA?
From:       Nicolas Pitre <nico () cam ! org>
Date:       2006-02-28 15:15:06
Message-ID: Pine.LNX.4.64.0602281009240.25336 () localhost ! localdomain
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On Mon, 20 Feb 2006, john orlando wrote:

> Hello,
> I have been reading through the kernel source looking for examples of drivers 
> that are using DMA on the PXA270 XScale platform.  I have only found a 
> handful of drivers that even mention using DMA on this platform:
> 
> /drivers/mmc/pxamci.c: complete(?) driver using scatter/gather dma to 
> interface to the on-chip MMC module

This is a good example.

> /drivers/net/smc91x.c: incomplete (?) driver that seems to request a dma 
> channel for receiving packets over dma, but doesn't seem to ever setup any of 
> the PXA270's DMA regs

It does sets up DMA regs.  It is indeed incomplete in the sense that DMA 
isn't used for transmission yet, and the DMA completion is polled.

> /drivers/serial/pxa.c: initial code present to request DMA channel, but 
> #ifdef'ed out (no other DMA support code present)

DMA is not yet implemented in that driver.

> /drivers/usb/gadget/pxa2xx_udc.c: driver contains code to support DMA, but is 
> apparently not compiled in since #USE_DMA is not defined

There are hardware bugs that prevents reliable DMa usage.

> Thats it.

No it is not.  You missed:

  sound/arm/pxa2xx-pcm.c

  drivers/net/irda/pxaficp_ir.c

which are additional fully functional DMA examples.


Nicolas



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