[alsa-devel] [PATCH 1/2] OMAP2+: DMA: Workaround for invalid source position

[Tony Lindgren]

* Peter Ujfalusi <peter.ujfalusi at ti.com> [111031 06:46]:
> 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 <peter.ujfalusi at ti.com>
> ---
>  arch/arm/plat-omap/dma.c |   15 +++++++++++++--
>  1 files changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm/plat-omap/dma.c b/arch/arm/plat-omap/dma.c
> index c22217c..38b0d44 100644
> --- a/arch/arm/plat-omap/dma.c
> +++ b/arch/arm/plat-omap/dma.c
> @@ -1024,12 +1024,23 @@ EXPORT_SYMBOL(omap_set_dma_callback);
>   */
>  dma_addr_t omap_get_dma_src_pos(int lch)
>  {
> +	u32 cdac;
>  	dma_addr_t offset = 0;
>  
>  	if (cpu_is_omap15xx())
>  		offset = p->dma_read(CPC, lch);
> -	else
> -		offset = p->dma_read(CSAC, lch);
> +	else {
> +		/*
> +		 * 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.
> +		 */
> +		cdac = p->dma_read(CDAC, lch);
> +		if (likely(cdac))
> +			offset = p->dma_read(CSAC, lch);
> +		else
> +			offset = p->dma_read(CSSA, lch);
> +	}
>  
>  	if (IS_DMA_ERRATA(DMA_ERRATA_3_3) && offset == 0)
>  		offset = p->dma_read(CSAC, lch);

Should these tests be done only after the errata re-read for both
src and dst patches? Otherwise the errata will not be handled?

Tony