From: vinod.koul@intel•com (Vinod Koul)
To: linux-arm-kernel@lists•infradead.org
Subject: DMA engine API issue (was: [PATCH/RFC 0/5] R-Car Gen2 DMAC hardware descriptor list support)
Date: Tue, 5 Aug 2014 22:26:17 +0530 [thread overview]
Message-ID: <20140805165617.GB8181@intel.com> (raw)
In-Reply-To: <1621896.RqTTnmY7rK@avalon>
On Mon, Aug 04, 2014 at 06:50:17PM +0200, Laurent Pinchart wrote:
> The question was why is there a dma_async_issue_pending() operation at all ?
> Why can't dmaengine_submit() triggers the transfer start ? The only
> explanation is a small comment in dmaengine.h that states
>
> * This allows drivers to push copies to HW in batches,
> * reducing MMIO writes where possible.
>
> I don't think that's applicable for DMA slave transfers. Is it still
> applicable for anything else ?
why not?
If your hw supports sg-lists and say length of 8 and you prepare two
descriptors for lengths of 3 and 5. While in issue pending what prevents you
from submiiting them in one shot to hardware while still getting interrupt.
I know designware and intel-dma do support that. It is different point that
drivers don't
--
~Vinod
next prev parent reply other threads:[~2014-08-05 16:56 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1406032431-3807-1-git-send-email-laurent.pinchart+renesas@ideasonboard.com>
[not found] ` <87d2cwvmxa.wl%kuninori.morimoto.gx@gmail.com>
[not found] ` <3361994.F0HgAeJkR9@avalon>
2014-07-23 11:07 ` DMA engine API issue (was: [PATCH/RFC 0/5] R-Car Gen2 DMAC hardware descriptor list support) Laurent Pinchart
2014-07-24 0:46 ` Kuninori Morimoto
2014-07-24 1:35 ` Kuninori Morimoto
2014-07-24 4:53 ` Vinod Koul
2014-07-24 4:52 ` Vinod Koul
2014-08-01 8:51 ` Laurent Pinchart
2014-08-01 14:30 ` Russell King - ARM Linux
2014-08-01 17:09 ` Vinod Koul
2014-08-04 13:47 ` Geert Uytterhoeven
2014-08-04 17:00 ` Laurent Pinchart
2014-08-04 17:54 ` Russell King - ARM Linux
2014-08-05 23:19 ` Laurent Pinchart
2014-08-06 7:17 ` Geert Uytterhoeven
2014-08-06 11:04 ` Arnd Bergmann
2014-08-01 17:07 ` Vinod Koul
2014-08-04 16:50 ` Laurent Pinchart
2014-08-04 18:03 ` DMA engine API issue Lars-Peter Clausen
2014-08-04 18:32 ` Russell King - ARM Linux
2014-08-04 23:12 ` Laurent Pinchart
2014-08-05 16:56 ` Vinod Koul [this message]
2014-07-24 12:29 ` [alsa-devel] " Lars-Peter Clausen
2014-07-24 12:51 ` DMA engine API issue (was: [PATCH/RFC 0/5] R-Car Gen2 DMAC hardware descriptor list support) Russell King - ARM Linux
2014-08-01 9:24 ` Laurent Pinchart
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