Re: [PATCH] fsldma: use PCI Read Multiple command

Li Yang
2009-04-27T10:16:31Z

On Mon, Apr 27, 2009 at 5:09 PM, Liu Dave-R63238 <DaveLiu@freescale.com> wrote:
>> By default, the Freescale 83xx DMA controller uses the PCI Read Line
>> command when reading data over the PCI bus. Setting the
>> controller to use the PCI Read Multiple command instead allows the
>> controller to read much larger bursts of data, which provides a
> drastic
>> speed increase.
>
> IIRC, the default for 83xx DMA controller uses the PCI mem read
> command, not mem read line.
>
> You are assuming the PCI memory space is prefetchable( no side effect)
> for DMA.
> Is it possible that DMA is from non-prefetchable memory space?

I guess it's not reasonable to use DMA from non-prefetchable memory.
So it's up to the driver which uses the DMA engine to prevent from
using DMA API on non-prefetchable memory.

- Leo