From: Rob Clark <robdclark@gmail.com>
To: Will Deacon <will.deacon@arm.com>
Cc: Sricharan R <sricharan@codeaurora.org>,
Vivek Gautam <vivek.gautam@codeaurora.org>,
Stephen Boyd <sboyd@codeaurora.org>,
Joerg Roedel <joro@8bytes.org>,
Robin Murphy <robin.murphy@arm.com>,
Rob Herring <robh+dt@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Marek Szyprowski <m.szyprowski@samsung.com>,
"iommu@lists.linux-foundation.org"
<iommu@lists.linux-foundation.org>,
"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
linux-clk <linux-clk@vger.kernel.org>,
linux-arm-msm <linux-arm-msm@vger.kernel.org>,
Stanimir Varbanov <stanimir.varbanov@linaro.org>,
Archit Taneja <architt@codeaurora.org>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH V4 3/6] iommu/arm-smmu: Invoke pm_runtime during probe, add/remove device
Date: Fri, 14 Jul 2017 13:42:13 -0400 [thread overview]
Message-ID: <CAF6AEGtMiVJvSrPXmQppM2NwS3fsXM8Vep3g0PwQK7SH4N=3xQ@mail.gmail.com> (raw)
In-Reply-To: <20170714170743.GA26488@arm.com>
On Fri, Jul 14, 2017 at 1:07 PM, Will Deacon <will.deacon@arm.com> wrote:
> On Thu, Jul 13, 2017 at 10:55:10AM -0400, Rob Clark wrote:
>> On Thu, Jul 13, 2017 at 9:53 AM, Sricharan R <sricharan@codeaurora.org> wrote:
>> > Hi,
>> >
>> > On 7/13/2017 5:20 PM, Rob Clark wrote:
>> >> On Thu, Jul 13, 2017 at 1:35 AM, Sricharan R <sricharan@codeaurora.org> wrote:
>> >>> Hi Vivek,
>> >>>
>> >>> On 7/13/2017 10:43 AM, Vivek Gautam wrote:
>> >>>> Hi Stephen,
>> >>>>
>> >>>>
>> >>>> On 07/13/2017 04:24 AM, Stephen Boyd wrote:
>> >>>>> On 07/06, Vivek Gautam wrote:
>> >>>>>> @@ -1231,12 +1237,18 @@ static int arm_smmu_map(struct iommu_domain *domain, unsigned long iova,
>> >>>>>> static size_t arm_smmu_unmap(struct iommu_domain *domain, unsigned long iova,
>> >>>>>> size_t size)
>> >>>>>> {
>> >>>>>> - struct io_pgtable_ops *ops = to_smmu_domain(domain)->pgtbl_ops;
>> >>>>>> + struct arm_smmu_domain *smmu_domain = to_smmu_domain(domain);
>> >>>>>> + struct io_pgtable_ops *ops = smmu_domain->pgtbl_ops;
>> >>>>>> + size_t ret;
>> >>>>>> if (!ops)
>> >>>>>> return 0;
>> >>>>>> - return ops->unmap(ops, iova, size);
>> >>>>>> + pm_runtime_get_sync(smmu_domain->smmu->dev);
>> >>>>> Can these map/unmap ops be called from an atomic context? I seem
>> >>>>> to recall that being a problem before.
>> >>>>
>> >>>> That's something which was dropped in the following patch merged in master:
>> >>>> 523d7423e21b iommu/arm-smmu: Remove io-pgtable spinlock
>> >>>>
>> >>>> Looks like we don't need locks here anymore?
>> >>>
>> >>> Apart from the locking, wonder why a explicit pm_runtime is needed
>> >>> from unmap. Somehow looks like some path in the master using that
>> >>> should have enabled the pm ?
>> >>>
>> >>
>> >> Yes, there are a bunch of scenarios where unmap can happen with
>> >> disabled master (but not in atomic context). On the gpu side we
>> >> opportunistically keep a buffer mapping until the buffer is freed
>> >> (which can happen after gpu is disabled). Likewise, v4l2 won't unmap
>> >> an exported dmabuf while some other driver holds a reference to it
>> >> (which can be dropped when the v4l2 device is suspended).
>> >>
>> >> Since unmap triggers tbl flush which touches iommu regs, the iommu
>> >> driver *definitely* needs a pm_runtime_get_sync().
>> >
>> > Ok, with that being the case, there are two things here,
>> >
>> > 1) If the device links are still intact at these places where unmap is called,
>> > then pm_runtime from the master would setup the all the clocks. That would
>> > avoid reintroducing the locking indirectly here.
>> >
>> > 2) If not, then doing it here is the only way. But for both cases, since
>> > the unmap can be called from atomic context, resume handler here should
>> > avoid doing clk_prepare_enable , instead move the clk_prepare to the init.
>> >
>>
>> I do kinda like the approach Marek suggested.. of deferring the tlb
>> flush until resume. I'm wondering if we could combine that with
>> putting the mmu in a stalled state when we suspend (and not resume the
>> mmu until after the pending tlb flush)?
>
> I'm not sure that a stalled state is what we're after here, because we need
> to take care to prevent any table walks if we've freed the underlying pages.
> What we could try to do is disable the SMMU (put into global bypass) and
> invalidate the TLB when performing a suspend operation, then we just ignore
> invalidation whilst the clocks are stopped and, on resume, enable the SMMU
> again.
wouldn't stalled just block any memory transactions by device(s) using
the context bank? Putting it in bypass isn't really a good thing if
there is any chance the device can sneak in a memory access before
we've taking it back out of bypass (ie. makes gpu a giant userspace
controlled root hole).
BR,
-R
> That said, I don't think we can tolerate suspend/resume racing with
> map/unmap, and it's not clear to me how we avoid that without penalising
> the fastpath.
>
> Will
next prev parent reply other threads:[~2017-07-14 17:42 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-07-06 9:36 [PATCH V4 0/6] iommu/arm-smmu: Add runtime pm/sleep support Vivek Gautam
2017-07-06 9:37 ` [PATCH V4 1/6] iommu/arm-smmu: Fix the error path in arm_smmu_add_device Vivek Gautam
2017-07-06 9:37 ` [PATCH V4 2/6] iommu/arm-smmu: Add pm_runtime/sleep ops Vivek Gautam
2017-07-12 22:58 ` Stephen Boyd
2017-07-12 23:01 ` Stephen Boyd
2017-07-13 3:57 ` Vivek Gautam
2017-07-06 9:37 ` [PATCH V4 3/6] iommu/arm-smmu: Invoke pm_runtime during probe, add/remove device Vivek Gautam
2017-07-12 22:54 ` Stephen Boyd
2017-07-13 5:13 ` Vivek Gautam
2017-07-13 5:35 ` Sricharan R
2017-07-13 11:50 ` Rob Clark
2017-07-13 12:02 ` Marek Szyprowski
2017-07-13 12:10 ` Rob Clark
2017-07-13 12:23 ` Marek Szyprowski
2017-07-13 13:53 ` Sricharan R
2017-07-13 14:55 ` Rob Clark
2017-07-14 17:07 ` Will Deacon
2017-07-14 17:42 ` Rob Clark [this message]
2017-07-14 18:06 ` Will Deacon
2017-07-14 18:25 ` Rob Clark
2017-07-14 19:01 ` Will Deacon
2017-07-14 19:34 ` Rob Clark
2017-07-14 19:36 ` Will Deacon
2017-07-14 19:39 ` Rob Clark
2017-07-17 11:46 ` Sricharan R
2017-07-17 12:28 ` Sricharan R
2017-07-24 15:31 ` Vivek Gautam
2017-08-02 9:53 ` [PATCH] iommu/arm-smmu: Defer TLB flush in case of unmap op Vivek Gautam
2017-08-02 12:17 ` Robin Murphy
2017-08-03 5:35 ` Vivek Gautam
2017-08-04 17:04 ` Robin Murphy
2017-08-07 7:44 ` Vivek Gautam
2017-08-07 8:27 ` [PATCH V4 3/6] iommu/arm-smmu: Invoke pm_runtime during probe, add/remove device Vivek Gautam
2017-08-07 12:29 ` Rob Clark
2017-11-14 18:30 ` Vivek Gautam
2017-11-27 22:22 ` Stephen Boyd
2017-11-27 23:43 ` Rob Clark
2017-11-28 13:43 ` Vivek Gautam
2017-11-28 20:05 ` Rob Clark
2017-07-13 13:57 ` Vivek Gautam
2017-07-13 14:01 ` Vivek Gautam
2017-07-13 6:48 ` Stephen Boyd
2017-07-13 9:50 ` Robin Murphy
2017-07-13 11:53 ` Rob Clark
2017-07-06 9:37 ` [PATCH V4 4/6] iommu/arm-smmu: Add the device_link between masters and smmu Vivek Gautam
2017-07-12 22:55 ` Stephen Boyd
2017-07-13 3:59 ` Vivek Gautam
2017-07-06 9:37 ` [PATCH V4 5/6] iommu/arm-smmu: Add support for MMU40x/500 clocks Vivek Gautam
2017-07-10 3:37 ` Rob Herring
2017-07-11 5:18 ` Vivek Gautam
2017-07-06 9:37 ` [PATCH V4 6/6] iommu/arm-smmu: Add support for qcom,msm8996-smmu-v2 clocks Vivek Gautam
2017-07-10 3:40 ` Rob Herring
2017-07-10 6:42 ` Vivek Gautam
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='CAF6AEGtMiVJvSrPXmQppM2NwS3fsXM8Vep3g0PwQK7SH4N=3xQ@mail.gmail.com' \
--to=robdclark@gmail.com \
--cc=architt@codeaurora.org \
--cc=devicetree@vger.kernel.org \
--cc=iommu@lists.linux-foundation.org \
--cc=joro@8bytes.org \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-arm-msm@vger.kernel.org \
--cc=linux-clk@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=m.szyprowski@samsung.com \
--cc=mark.rutland@arm.com \
--cc=robh+dt@kernel.org \
--cc=robin.murphy@arm.com \
--cc=sboyd@codeaurora.org \
--cc=sricharan@codeaurora.org \
--cc=stanimir.varbanov@linaro.org \
--cc=vivek.gautam@codeaurora.org \
--cc=will.deacon@arm.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).