Re: [PATCH 2/5] musb: use system DMA to fix Inventra DMA issue on RTL-1.4

[Felipe Balbi <me-uiRdBs8odbtmTBlB0Cgj/Q@public.gmane.org>]

On Wed, May 12, 2010 at 05:19:36PM +0530, Ajay Kumar Gupta wrote:
> MUSB RTL version 1.4 has a hardware issue when TX and RX DMA channels are
> simultaneously enabled which results in DMA lockup.

I've seen it on rtl1.8 also if I remember correctly.

> Use system DMA for all RX channels as a workaround of this issue as this
> will have minimal throughput overhead based on the fact that Rx transfers
> are done in DMA mode-0 on OMAP34x/35x platforms.
> 
> Another approach to use PIO mode in opposite direction would increase the
> cpu loading and thus using system DMA is preferred workaround.
> 
> Signed-off-by: Anand Gadiyar <gadiyar-l0cyMroinI0@public.gmane.org>
> Signed-off-by: Ajay Kumar Gupta <ajay.gupta-l0cyMroinI0@public.gmane.org>

I think falling back to pio is better than this patch. It will most
likely be only one transfer. Another approach is to allocate dma
channels on a transfer basis. This is way too big of a problem.

-- 
balbi
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