linux-kernel - Re: [PATCH 2/2] dw_dmac: return proper residue value

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Date:	Mon, 21 Jan 2013 00:49:24 -0800
From:	Vinod Koul <vinod.koul@...el.com>
To:	Andy Shevchenko <andriy.shevchenko@...ux.jf.intel.com>
Cc:	Viresh Kumar <viresh.linux@...il.com>,
	linux-kernel@...r.kernel.org, spear-devel <spear-devel@...t.st.com>
Subject: Re: [PATCH 2/2] dw_dmac: return proper residue value

On Mon, Jan 21, 2013 at 11:00:44AM +0200, Andy Shevchenko wrote:
> Currently the driver returns full length of the active descriptor which is
> wrong. We have to go throught the active descriptor and sum up the length of
> unsent children in the chain along with the actual data in the DMA channel
why do you mean by children here?
> registers.
> 
> The cyclic case is not handled by this patch due to len field in the descriptor
> structure is left untouched by the original code.
> 
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> ---
>  drivers/dma/dw_dmac.c |   93 ++++++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 92 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/dma/dw_dmac.c b/drivers/dma/dw_dmac.c
> index d1b9ba2..4325c68 100644
> --- a/drivers/dma/dw_dmac.c
> +++ b/drivers/dma/dw_dmac.c
> @@ -941,6 +941,97 @@ err_desc_get:
>  	return NULL;
>  }
>  
> +/* --------------------- Calculate residue ---------------------------- */
> +
> +static inline size_t dwc_get_rest(struct dw_dma_chan *dwc, struct dw_desc *desc)
> +{
> +	enum dma_transfer_direction direction = dwc->direction;
> +
> +	if (direction == DMA_MEM_TO_DEV || direction == DMA_MEM_TO_MEM)
> +		return desc->len - (channel_readl(dwc, SAR) - desc->lli.sar);
> +	else if (direction == DMA_DEV_TO_MEM)
> +		return desc->len - (channel_readl(dwc, DAR) - desc->lli.dar);
> +
> +	return 0;
hmmm, why not use BLOCK_TS value. That way you dont need to look at direction
and along with burst can easily calculate residue...

--
~Vinod
--
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