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[34.142.210.164]) by smtp.gmail.com with ESMTPSA id a92af1059eb24-1432435648esm45959637c88.5.2026.09.08.13.23.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 08 Sep 2026 13:23:56 -0700 (PDT) Date: Tue, 8 Sep 2026 20:23:49 +0000 From: Pranjal Shrivastava To: Thomas Gleixner Cc: iommu@lists.linux.dev, Will Deacon , Joerg Roedel , Robin Murphy , Jason Gunthorpe , Mostafa Saleh , Nicolin Chen , Daniel Mentz , Ashish Mhetre , linux-arm-kernel@lists.infradead.org, Greg Kroah-Hartman , rafael@kernel.org, Danilo Krummrich , driver-core@lists.linux.dev Subject: Re: [PATCH v10 08/15] iommu/arm-smmu-v3: Cache and restore MSI config Message-ID: References: <20260908171712.356645-1-praan@google.com> <20260908171712.356645-9-praan@google.com> <87pkyn1pqm.ffs@fw13> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <87pkyn1pqm.ffs@fw13> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260908_132359_115555_D4EFCF12 X-CRM114-Status: GOOD ( 27.12 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, Sep 08, 2026 at 09:56:33PM +0200, Thomas Gleixner wrote: > On Tue, Sep 08 2026 at 17:17, Pranjal Shrivastava wrote: > > +static void __maybe_unused arm_smmu_resume_msis(struct arm_smmu_device *smmu) > > +{ > > + /* Clear the MSI address regs as they reset to unknown value */ > > + writeq_relaxed(0, smmu->base + ARM_SMMU_GERROR_IRQ_CFG0); > > + writeq_relaxed(0, smmu->base + ARM_SMMU_EVTQ_IRQ_CFG0); > > + > > + if (smmu->features & ARM_SMMU_FEAT_PRI) > > + writeq_relaxed(0, smmu->base + ARM_SMMU_PRIQ_IRQ_CFG0); > > + > > + if (!(smmu->features & ARM_SMMU_FEAT_MSI)) > > + return; > > + > > + if (!smmu->dev->msi.domain) { > > + dev_err(smmu->dev, "msi_domain absent during resume\n"); > > + smmu->features &= ~ARM_SMMU_FEAT_MSI; > > + return; > > If dev->msi.domain == NULL then arm_smmu_setup_msis() already cleared > the MSI feature bit. Has it magically been set again or does resume run > before init or does dev->msi.domain magically disappear during suspend? > > I'm all for defensive programming, but this is voodoo and not structured > defense. > > Aside of that dev->msi.domain is the patently wrong condition. For > devices which instantiate a MSI device domain dev->msi.domain points to > the MSI parent domain and not to the actual relevant device domain. > > You can't query that easily by chasing pointers (for a reason), but > there is no point to do so. See below and the patch I sent you. > Guilty of voodoo defense. You're completely right—FEAT_MSI was already vleared on fallback during probe, and checking the parent domain here was misguided. Dropping that entirely. (I added the check here and then updated the setup_msis() part). > > + platform_device_msi_rewrite(smmu->dev, smmu->gerr_irq, arm_smmu_write_msi_msg); > > + platform_device_msi_rewrite(smmu->dev, smmu->evtq.q.irq, arm_smmu_write_msi_msg); > > + > > + if (smmu->features & ARM_SMMU_FEAT_PRI) > > + platform_device_msi_rewrite(smmu->dev, smmu->priq.q.irq, arm_smmu_write_msi_msg); > > And that's exactly the point I made about sprinkling this stuff all over > the place and thereby violating all layering rules. > > Done correctly this whole function boils down to: > > static void __maybe_unused arm_smmu_resume_msis(struct arm_smmu_device *smmu) > { > /* Clear the MSI address regs as they reset to unknown value */ > writeq_relaxed(0, smmu->base + ARM_SMMU_GERROR_IRQ_CFG0); > writeq_relaxed(0, smmu->base + ARM_SMMU_EVTQ_IRQ_CFG0); > > if (smmu->features & ARM_SMMU_FEAT_PRI) > writeq_relaxed(0, smmu->base + ARM_SMMU_PRIQ_IRQ_CFG0); > > msi_device_domain_restore_msi_msgs(smmu->dev, 0); > } > > It just works simply because the function returns early when there is no > domain or the domain is not a MSI device domain, which is correct > because there is nothing to do when nothing is set up. > > But that results in too comprehensible code I fear. > I certainly won't complain about code being too comprehensible! :) This is much cleaner than what I had. I'll drop my implementation of patch 7 (platform_device_msi_rewrite) completely in favor of your core msi_device_domain_restore_msi_msgs() helper, simplify patch 8 to this and take it for a spin. Thanks, Praan