From: geert@linux-m68k.org (Geert Uytterhoeven)
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: Mon, 4 Aug 2014 15:47:51 +0200 [thread overview]
Message-ID: <CAMuHMdWSe8m2yRV5fhLfZ=gbGUev6ExD+0eQ_nKK84SRs1DEwQ@mail.gmail.com> (raw)
In-Reply-To: <20140801143020.GQ30282@n2100.arm.linux.org.uk>
Hi Russell,
On Fri, Aug 1, 2014 at 4:30 PM, Russell King - ARM Linux
<linux@arm.linux.org.uk> wrote:
> On Fri, Aug 01, 2014 at 10:51:26AM +0200, Laurent Pinchart wrote:
>> I'll take this opportunity to question why we have a separation between
>> tx_submit and issue_pending. What's the rationale for that, especially given
>> that dma_issue_pending_all() might kick in at any point and issue pending
>> transfers for all devices. A driver could thus see its submitted but not
>> issued transactions being issued before it explicitly calls
>> dma_async_issue_pending().
>
> A prepared but not submitted transaction is not a pending transaction.
>
> The split is necessary so that a callback can be attached to the
> transaction. This partially comes from the async-tx API, and also
> gets a lot of use with the slave API.
>
> The prepare function allocates the descriptor and does the initial
> setup, but does not mark the descriptor as a pending transaction.
> It returns the descriptor, and the caller is then free to add a
> callback function and data pointer to the descriptor before finally
> submitting it. This sequence must occur in a timely manner as some
> DMA engine implementations hold a lock between the prepare and submit
> callbacks (Dan explicitly permits this as part of the API.)
I think you misunderstood the question: Laurent asked about
dmaengine_submit() (step 2) and dma_async_issue_pending() (step 3),
while your answer is about dmaengine_prep_slave_*() (step 1) and
dmaengine_submit() (step 2).
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
next prev parent reply other threads:[~2014-08-04 13:47 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 [this message]
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 ` DMA engine API issue (was: [PATCH/RFC 0/5] R-Car Gen2 DMAC hardware descriptor list support) Vinod Koul
2014-07-24 12:29 ` [alsa-devel] DMA engine API issue 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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