From: Sascha Hauer <s.hauer@pengutronix.de>
To: Robin Gong <yibin.gong@nxp.com>
Cc: "alsa-devel@alsa-project.org" <alsa-devel@alsa-project.org>,
Lars-Peter Clausen <lars@metafoo.de>,
"timur@kernel.org" <timur@kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"nicoleotsuka@gmail.com" <nicoleotsuka@gmail.com>,
"vkoul@kernel.org" <vkoul@kernel.org>,
Benjamin Bara - SKIDATA <Benjamin.Bara@skidata.com>,
"kernel@pengutronix.de" <kernel@pengutronix.de>,
"dmaengine@vger.kernel.org" <dmaengine@vger.kernel.org>,
"dan.j.williams@intel.com" <dan.j.williams@intel.com>,
Richard Leitner - SKIDATA <Richard.Leitner@skidata.com>,
"shawnguo@kernel.org" <shawnguo@kernel.org>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
dl-linux-imx <linux-imx@nxp.com>
Subject: Re: pcm|dmaengine|imx-sdma race condition on i.MX6
Date: Tue, 25 Aug 2020 08:12:48 +0200 [thread overview]
Message-ID: <20200825061247.GL13023@pengutronix.de> (raw)
In-Reply-To: <VE1PR04MB66386A43E2BCC5B758D1A71A895B0@VE1PR04MB6638.eurprd04.prod.outlook.com>
On Fri, Aug 21, 2020 at 09:52:00AM +0000, Robin Gong wrote:
> On 2020/08/20 14:52 Sascha Hauer <s.hauer@pengutronix.de> wrote:
> > On Wed, Aug 19, 2020 at 01:08:29PM +0200, Lars-Peter Clausen wrote:
> > > > For the first option, which is potentially more performant, we have
> > > > to leave the atomic PCM context and we are not sure if we are allowed to.
> > > > For the second option, we would have to divide the dma_device
> > > > terminate_all into an atomic sync and an async one, which would
> > > > align with the dmaengine API, giving it the option to ensure termination in
> > an atomic context.
> > > > Based on my understanding, most of them are synchronous anyways, for
> > > > the currently async ones we would have to implement busy waits.
> > > > However, with this approach, we reach the WARN_ON [6] inside of an
> > > > atomic context, indicating we might not do the right thing.
> > >
> > > I don't know how feasible this is to implement in the SDMA dmaengine
> > driver.
> > > But I think what is should do is to have some flag to indicate if a
> > > terminate is in progress. If a new transfer is issued while terminate
> > > is in progress the transfer should go on a list. Once terminate
> > > finishes it should check the list and start the transfer if there are any on the
> > list.
> >
> > The list is already there in form of the vchan helpers the driver uses.
> Seems Lars major concern is on the race condition between next descriptor
> and sdma_channel_terminate_work which free the last terminated descriptor,
> not the ability of vchan to support multi descriptors. But anyway, I think we
> should take care vchan_get_all_descriptors to free descriptors during terminate
> phase in case it's done in worker like sdma_channel_terminate_work, since that
> may free the next descriptor wrongly. That's what my patch attached in
> 0001-dmaengine-imx-sdma-add-terminated-list-for-freed-des.patch
> https://www.spinics.net/lists/arm-kernel/msg829972.html
Indeed this should solve the problem of freeing descriptors allocated
between terminate_all and a following prep_slave*.
>
> >
> > I think the big mistake the driver makes is to configure fields in struct
> > sdma_channel and also the hardware directly in sdma_prep_memcpy(),
> > sdma_prep_slave_sg() and sdma_prep_dma_cyclic(). All information should be
> > stored in the struct sdma_desc allocated in the prep functions and only be used
> > when it's time to fire that specific descriptor.
> Sorry Sascha, seems that's another topic and your intention is to make sure only
> software involved in sdma_prep_* and all HW moved into one function inside
> sdma_start_desc. I agree that will make code more clean but my concern is
> sdma_start_desc is protect by spin_lock which should be short as possible while
> some HW touch as context_load may cost some time. Anyway, that's another topic,
> maybe we can refine it in the future.
Yes, you are right. This is another topic.
Sascha
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prev parent reply other threads:[~2020-08-25 6:14 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-13 11:22 pcm|dmaengine|imx-sdma race condition on i.MX6 Richard Leitner
2020-08-14 8:45 ` Robin Gong
[not found] ` <7f98cd6d30404e4d9d621f57f45ae441@skidata.com>
2020-08-17 5:38 ` Richard Leitner
2020-08-17 7:28 ` Benjamin Bara - SKIDATA
2020-08-17 9:22 ` Robin Gong
2020-08-17 11:38 ` Benjamin Bara - SKIDATA
2020-08-18 10:41 ` Robin Gong
2020-08-19 11:08 ` Lars-Peter Clausen
2020-08-19 11:16 ` Lars-Peter Clausen
2020-08-19 14:15 ` Benjamin Bara - SKIDATA
2020-08-19 14:25 ` Benjamin Bara - SKIDATA
2020-08-20 15:01 ` Robin Gong
2020-08-21 4:34 ` Richard Leitner
2020-08-21 9:21 ` Robin Gong
2020-08-21 9:54 ` Richard Leitner
2020-08-20 6:52 ` Sascha Hauer
2020-08-21 9:52 ` Robin Gong
2020-08-25 6:12 ` Sascha Hauer [this message]
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