Re: [PATCH 4/5] musb: use system DMA for unaligned buffers on RTL >= 1.8

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

On Wed, May 12, 2010 at 05:19:38PM +0530, Ajay Kumar Gupta wrote:
> MUSB RTL version 1.8 onward (OMAP3630, AM/DM37x, OMAP4) DMA requires
> the buffers to be aligned on a four byte boundary. This affects USB
> CDC/RNDIS class application where buffers are always unaligned.
> 
> Use system DMA for unaligned buffers as a workaround of this issue.
> 
> Current patch supports device side CDC/RNDIS. Host side would require
> change in Tx programming path for mode-0 operation when transfer length
> is more than packet size.
> 
> Also fixed an issue in device Tx completion path where 'is_dma' is getting
> set unconditionally. This would fail the io if Tx transfer is done in
> mode-0. Fixed it by updating it based on 'request->actual' length.
> 
> Signed-off-by: Ajay Kumar Gupta <ajay.gupta-l0cyMroinI0@public.gmane.org>

[..]

> @@ -166,6 +166,12 @@ config MUSB_USE_SYSTEM_DMA_WORKAROUND
>            DMA channels are simultaneously enabled. To work around this issue,
>            you can choose to use System DMA for RX channels.
>  
> +	  Also on Mentor DMA in MUSB RTL version 1.8 (OMAP3630, AM/DM37x)
> +	  requires buffers to be aligned on a four byte boundary. This affects
> +	  USB CDC/RNDIS class application where buffers are always unaligned.
> +	  To work around this issue, you can choose to use System DMA for
> +	  unaligned buffers.

instead of this patch, it's a whole lot easier to simply use a bounce
buffer:

if (unaligned) {
	bounce = dma_alloc_coherent(......);
	memcpy(request->buf, bounce, request->length);
}

and use that buffer on channel_program();

-- 
balbi
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