Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751069AbdGNTBN (ORCPT ); Fri, 14 Jul 2017 15:01:13 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:51704 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750819AbdGNTBL (ORCPT ); Fri, 14 Jul 2017 15:01:11 -0400 Date: Fri, 14 Jul 2017 20:01:14 +0100 From: Will Deacon To: Rob Clark Cc: Sricharan R , Vivek Gautam , Stephen Boyd , Joerg Roedel , Robin Murphy , Rob Herring , Mark Rutland , Marek Szyprowski , "iommu@lists.linux-foundation.org" , "devicetree@vger.kernel.org" , Linux Kernel Mailing List , linux-clk , linux-arm-msm , Stanimir Varbanov , Archit Taneja , "linux-arm-kernel@lists.infradead.org" Subject: Re: [PATCH V4 3/6] iommu/arm-smmu: Invoke pm_runtime during probe, add/remove device Message-ID: <20170714190113.GE26488@arm.com> References: <20170712225459.GZ22780@codeaurora.org> <5ee0bacd-e557-a6c4-a897-844fb12ea6ae@codeaurora.org> <4dbc938c-ac88-9bd4-cf00-458008ae24c1@codeaurora.org> <60a56ae6-ed9d-57cd-130f-5bd9d32d4d58@codeaurora.org> <20170714170743.GA26488@arm.com> <20170714180615.GC26488@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5600 Lines: 107 On Fri, Jul 14, 2017 at 02:25:45PM -0400, Rob Clark wrote: > On Fri, Jul 14, 2017 at 2:06 PM, Will Deacon wrote: > > On Fri, Jul 14, 2017 at 01:42:13PM -0400, Rob Clark wrote: > >> On Fri, Jul 14, 2017 at 1:07 PM, Will Deacon 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 wrote: > >> >> > Hi, > >> >> > > >> >> > On 7/13/2017 5:20 PM, Rob Clark wrote: > >> >> >> On Thu, Jul 13, 2017 at 1:35 AM, Sricharan R 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). > > > > If it doesn't deadlock, then yes, it will stall transactions. However, that > > doesn't mean it necessarily prevents page table walks. > > btw, I guess the concern about pagetable walk is that the unmap could > have removed some sub-level of the pt that the tlb walk would hit? > Would deferring freeing those pages help? Could do, but it sounds like a lot of complication that I think we can fix by making the suspend operation put the SMMU into a "clean" state. > > Instead of bypass, we > > could configure all the streams to terminate, but this race still worries me > > somewhat. I thought that the SMMU would only be suspended if all of its > > masters were suspended, so if the GPU wants to come out of suspend then the > > SMMU should be resumed first. > > I believe this should be true.. on the gpu side, I'm mostly trying to > avoid having to power the gpu back on to free buffers. (On the v4l2 > side, somewhere in the core videobuf code would also need to be made > to wrap it's dma_unmap_sg() with pm_runtime_get/put()..) Right, and we shouldn't have to resume it if we suspend it in a clean state, with the TLBs invalidated. Will