linux-kernel - Re: [PATCH 1/4] dmaengine/dw_dmac: don't scan descriptors if no xfers in progress

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Date:	Fri, 3 Dec 2010 15:20:01 -0800
From:	Dan Williams <dan.j.williams@...el.com>
To:	Jamie Iles <jamie@...ieiles.com>
Cc:	linux-kernel@...r.kernel.org, Jamie Iles <jamie.iles@...ochip.com>,
	hskinnemoen@...il.com
Subject: Re: [PATCH 1/4] dmaengine/dw_dmac: don't scan descriptors if no xfers
 in progress

[ copying Haavard's new address ]

On Tue, Nov 23, 2010 at 3:06 AM, Jamie Iles <jamie@...ieiles.com> wrote:
> Some hardware (picoChip picoXCell in particular) sometimes has
> the block transfer complete bit being set for a channel after the
> whole transfer has completed. If we don't have any transfers in the
> active list then don't bother to scan the descriptors. This often
> happens in normal operation and doesn't require the channel to be
> reset.
>
> Cc: Haavard Skinnemoen <haavard.skinnemoen@...el.com>
> Cc: Dan Williams <dan.j.williams@...el.com>
> Signed-off-by: Jamie Iles <jamie.iles@...ochip.com>
> ---
>  drivers/dma/dw_dmac.c |    3 +++
>  1 files changed, 3 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/dma/dw_dmac.c b/drivers/dma/dw_dmac.c
> index a3991ab..08c51d4 100644
> --- a/drivers/dma/dw_dmac.c
> +++ b/drivers/dma/dw_dmac.c
> @@ -291,6 +291,9 @@ static void dwc_scan_descriptors(struct dw_dma *dw, struct dw_dma_chan *dwc)
>                return;
>        }
>
> +        if (list_empty(&dwc->active_list))
> +                return;
> +
>        dev_vdbg(chan2dev(&dwc->chan), "scan_descriptors: llp=0x%x\n", llp);
>
>        list_for_each_entry_safe(desc, _desc, &dwc->active_list, desc_node) {
> --
> 1.7.2.3
>
> --
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