From: Vinod Koul <vinod.koul@linaro.org>
To: Frank Mori Hess <fmh6jj@gmail.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>,
dmaengine@vger.kernel.org, linux-kernel@vger.kernel.org,
Dan Williams <dan.j.williams@intel.com>,
r.baldyga@hackerion.com, Krzysztof Kozlowski <krzk@kernel.org>,
Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
Linux Samsung SOC <linux-samsung-soc@vger.kernel.org>
Subject: Re: Revert "dmaengine: pl330: add DMA_PAUSE feature"
Date: Thu, 17 May 2018 09:49:46 +0530 [thread overview]
Message-ID: <20180517041946.GQ13271@vkoul-mobl> (raw)
In-Reply-To: <CAJz5Open++Dj=a4ty-JbnZBFoqbMQKU6qYumJKSRMRLp_3erSw@mail.gmail.com>
On 15-05-18, 11:50, Frank Mori Hess wrote:
> On Tue, May 15, 2018 at 2:21 AM, Vinod <vkoul@kernel.org> wrote:
> >
> > For Pause/resume data loss is _not_ expected.
> >
> >> > and some of the 8250 drivers like 8250_dw.c set a maxburst > 1. If it
> >> > can't count on the pause/residue/terminate working without data loss
> >> > then it is just broken. As is the 8250_omap.c driver. Is the
> >> > description of dmaengine_pause in the documentation of "This pauses
> >> > activity on the DMA channel without data loss" to be interpreted as
> >> > "as long as you resume afterwards"?
> >>
> >> I assume that this requirement is for both - resuming and terminating.
> >
> > Terminate is abort, data loss may happen here.
>
> Wait, are you saying if you do
>
> dma pause
no data loss
> read residue
here as well
> dma terminate
Oh yes, we aborted...
>
> then it is acceptable for there to be data loss, because it can be
> blamed on the terminate? In that case the usage of dmaengine in all
> the 8250 serial drivers is broken. Every time there is a break in the
> incoming rx data, the 8250 driver does pause/residue/terminate which
> could potentially cause data from the incoming data stream to be
> dropped.
As I said terminate is abort. It cleans up the channel and is supposed to
used for cleanup not for stopping. See Documentation:
- device_terminate_all
- Aborts all the pending and ongoing transfers on the channel
- For aborted transfers the complete callback should not be called
- Can be called from atomic context or from within a complete
callback of a descriptor. Must not sleep. Drivers must be able
to handle this correctly.
- Termination may be asynchronous. The driver does not have to
wait until the currently active transfer has completely stopped.
See device_synchronize.
Thanks
--
~Vinod
next prev parent reply other threads:[~2018-05-17 4:19 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-28 21:50 [PATCH] Revert "dmaengine: pl330: add DMA_PAUSE feature" Frank Mori Hess
2018-05-02 4:32 ` Vinod Koul
2018-05-02 14:37 ` Frank Mori Hess
2018-05-03 9:01 ` Vinod Koul
2018-05-03 16:35 ` Vinod Koul
[not found] ` <CGME20180508090407eucas1p13713284c2d3f5aa5c66f8d136be683c1@eucas1p1.samsung.com>
2018-05-08 9:04 ` Marek Szyprowski
2018-05-08 14:36 ` Frank Mori Hess
2018-05-09 6:59 ` Vinod Koul
2018-05-09 13:19 ` Marek Szyprowski
2018-05-09 17:48 ` Frank Mori Hess
2018-05-10 8:31 ` Marek Szyprowski
2018-05-10 16:04 ` Frank Mori Hess
2018-05-11 12:57 ` Marek Szyprowski
2018-05-11 15:57 ` Frank Mori Hess
2018-05-15 6:21 ` Vinod
2018-05-15 12:24 ` Marek Szyprowski
2018-05-15 13:45 ` Vinod
2018-05-15 15:50 ` Frank Mori Hess
2018-05-17 4:19 ` Vinod Koul [this message]
2018-05-17 16:20 ` Frank Mori Hess
2018-05-17 17:22 ` Lars-Peter Clausen
2018-05-18 19:01 ` Frank Mori Hess
2018-05-18 4:03 ` Vinod
2018-05-18 6:28 ` Marek Szyprowski
2018-05-18 7:21 ` Vinod
2018-05-29 5:17 ` Marek Szyprowski
2018-05-29 7:09 ` Vinod
2018-05-18 18:56 ` Frank Mori Hess
2018-05-21 9:16 ` Vinod Koul
2018-05-22 0:56 ` Frank Mori Hess
2018-05-22 3:37 ` Vinod Koul
2018-05-22 14:27 ` Frank Mori Hess
2018-05-23 5:39 ` Vinod
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