Subject: [PATCH v2 1/2] OMAP2+: DMA: Workaround for invalid source position

From: [email-masked] (Jarkko Nikula)
Date: Thu, 10 Nov 2011 14:46:22 +0200

On 11/07/2011 11:33 AM, Peter Ujfalusi wrote:
> If the DMA source position has been asked before the
> first actual data transfer has been done, the CSAC
> register does not contain valid information.
> We can identify this situation by checking the CDAC
> register:
> CDAC != 0 indicates that the DMA transfer on the channel has
> been started already.
> When CDAC == 0 we can not trust the CSAC value since it has
> not been updated, and can contain random number.
> Return the start address in case the DMA has not jet started.
>
> Note: The CDAC register has been initialized to 0 at dma_start
> time.
>
> Signed-off-by: Peter Ujfalusi<[email-masked]>
> ---
>   arch/arm/plat-omap/dma.c |   12 ++++++++++++
>   1 files changed, 12 insertions(+), 0 deletions(-)
>
> diff --git a/arch/arm/plat-omap/dma.c b/arch/arm/plat-omap/dma.c
> index c22217c..a9983b6 100644
> --- a/arch/arm/plat-omap/dma.c
> +++ b/arch/arm/plat-omap/dma.c
> @@ -1034,6 +1034,18 @@ dma_addr_t omap_get_dma_src_pos(int lch)
>   	if (IS_DMA_ERRATA(DMA_ERRATA_3_3)&&  offset == 0)
>   		offset = p->dma_read(CSAC, lch);
>
> +	if (!cpu_is_omap15xx()) {
> +		/*
> +		 * CDAC == 0 indicates that the DMA transfer on the channel has
> +		 * not been started (no data has been transferred so far).
> +		 * Return the programmed source start address in this case.
> +		 */
> +		if (likely(p->dma_read(CDAC, lch)))
> +			offset = p->dma_read(CSAC, lch);
> +		else
> +			offset = p->dma_read(CSSA, lch);
> +	}
> +

I think this is enough:

if (unlikely(p->dma_read(CDAC, lch) == 0))
	offset = p->dma_read(CSSA, lch);

I suppose offset is ok for normal case as it is already read (twise) above.

-- 
Jarkko