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[34.124.234.44]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2baf1d2700dsm29924885ad.2.2026.05.08.09.58.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 08 May 2026 09:58:31 -0700 (PDT) Date: Fri, 8 May 2026 16:58:25 +0000 From: Pranjal Shrivastava To: Jason Gunthorpe Cc: iommu@lists.linux.dev, Jonathan Hunter , Joerg Roedel , linux-arm-kernel@lists.infradead.org, linux-tegra@vger.kernel.org, Robin Murphy , Thierry Reding , Krishna Reddy , Will Deacon , David Matlack , Pasha Tatashin , patches@lists.linux.dev, Samiullah Khawaja , Mostafa Saleh Subject: Re: [PATCH 2/9] iommu/arm-smmu-v3: Use the HW arm_smmu_cmd in cmdq selection functions Message-ID: References: <0-v1-b7dc0a0d4aa0+3723d-smmu_no_cmdq_ent_jgg@nvidia.com> <2-v1-b7dc0a0d4aa0+3723d-smmu_no_cmdq_ent_jgg@nvidia.com> <20260508155432.GE9254@nvidia.com> Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260508155432.GE9254@nvidia.com> On Fri, May 08, 2026 at 12:54:32PM -0300, Jason Gunthorpe wrote: > On Fri, May 08, 2026 at 07:47:45AM +0000, Pranjal Shrivastava wrote: > > On Fri, May 01, 2026 at 11:29:11AM -0300, Jason Gunthorpe wrote: > > > Start removing the use of struct arm_smmu_cmdq_ent, starting at the > > > lower levels of the call chain. Change the functions that determine what > > > cmdq to issue the batch to into using struct arm_smmu_cmd directly. > > > > > > Signed-off-by: Jason Gunthorpe > > > --- > > > drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 47 ++++++++++++------- > > > drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h | 8 ++-- > > > .../iommu/arm/arm-smmu-v3/tegra241-cmdqv.c | 8 ++-- > > > 3 files changed, 38 insertions(+), 25 deletions(-) > > > > [...] > > > > > index = cmds->num * CMDQ_ENT_DWORDS; > > > - if (unlikely(arm_smmu_cmdq_build_cmd(&cmds->cmds[index], cmd))) { > > > - dev_warn(smmu->dev, "ignoring unknown CMDQ opcode 0x%x\n", > > > - cmd->opcode); > > > - return; > > > - } > > > - > > > + memcpy(&cmds->cmds[index], cmd.data, sizeof(cmd.data)); > > > cmds->num++; > > > } > > > > The memcpy is a temporary step and goes way in Patch 4. > > To be clear patch 4 still has the memcpy: > > - index = cmds->num * CMDQ_ENT_DWORDS; > - memcpy(&cmds->cmds[index], cmd.data, sizeof(cmd.data)); > - cmds->num++; > + cmds->cmds[cmds->num++] = cmd; > ^^^^^^^^^^^ > > The compiler just builds it. > > The flow evolution is: > > Now: > struct arm_smmu_cmdq_ent (stack) -> arm_smmu_cmdq_build_cmd (batch) -> memcpy (queue) > Here: > struct arm_smmu_cmdq_ent (stack) -> arm_smmu_cmdq_build_cmd (stack) -> memcpy (batch) -> memcpy (queue) > Done: > struct arm_smmu_cmd (stack) -> memcpy (batch) -> memcpy (queue) > > So the net result is the same before/after this series, we just carry > an extra stack copy till the last patch. Right that makes sense. N Thanks, Praan