From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751732AbdGMLxr (ORCPT ); Thu, 13 Jul 2017 07:53:47 -0400 Received: from mail-lf0-f66.google.com ([209.85.215.66]:35492 "EHLO mail-lf0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751050AbdGMLxp (ORCPT ); Thu, 13 Jul 2017 07:53:45 -0400 MIME-Version: 1.0 In-Reply-To: References: <1499333825-7658-1-git-send-email-vivek.gautam@codeaurora.org> <1499333825-7658-4-git-send-email-vivek.gautam@codeaurora.org> <20170712225459.GZ22780@codeaurora.org> <5ee0bacd-e557-a6c4-a897-844fb12ea6ae@codeaurora.org> <20170713064843.GX22780@codeaurora.org> From: Rob Clark Date: Thu, 13 Jul 2017 07:53:42 -0400 Message-ID: Subject: Re: [PATCH V4 3/6] iommu/arm-smmu: Invoke pm_runtime during probe, add/remove device To: Robin Murphy Cc: Stephen Boyd , Vivek Gautam , Joerg Roedel , Rob Herring , Mark Rutland , Will Deacon , Marek Szyprowski , "iommu@lists.linux-foundation.org" , "devicetree@vger.kernel.org" , Linux Kernel Mailing List , linux-clk , linux-arm-msm , Sricharan R , Stanimir Varbanov , Archit Taneja , "linux-arm-kernel@lists.infradead.org" Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jul 13, 2017 at 5:50 AM, Robin Murphy wrote: > On 13/07/17 07:48, Stephen Boyd wrote: >> On 07/13, 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? >>> >> >> While removing the spinlock around the map/unmap path may be one >> thing, I'm not sure that's all of them. Is there a path from an >> atomic DMA allocation (GFP_ATOMIC sort of thing) mapped into an >> IOMMU for a device that can eventually get down to here and >> attempt to turn a clk on? > > Yes, in the DMA path map/unmap will frequently be called from IRQ > handlers (think e.g. network packets). The whole point of removing the > lock was to allow multiple maps/unmaps to execute in parallel (since we > know they will be safely operating on different areas of the pagetable). > AFAICS this change is going to largely reintroduce that bottleneck via > dev->power_lock, which is anything but what we want :( > Maybe __pm_runtime_resume() needs some sort of fast-path if already enabled? Or otherwise we need some sort of flag to tell the iommu that it cannot rely on the unmapping device to be resumed? BR, -R