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a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1561395834; bh=jD2uK5kCwexPBSnlloDzcLqIftPyzxTGZFnE/+MKxQM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=flxl+4YatLVLP2cePA3e4X7Wh66OFz4Df7unTW3gX7IS3uVUqtmUW+bqjszBy3MvG B5+DWZMnFBCVb3RpJ84i30TPyvr0bD5egtvEfqu+i+MV+3OoTkg4GQIa76HRa4YYRU Rrf1OiPhakYPRzxa7pXFv2aNJhrv/KGzo07Sm2To= Date: Mon, 24 Jun 2019 18:03:49 +0100 From: Will Deacon To: Vivek Gautam Subject: Re: [PATCH v3 3/4] iommu/arm-smmu: Add support to handle Qcom's wait-for-safe logic Message-ID: <20190624170348.7dncuc5qezqeyvq2@willie-the-truck> References: <20190612071554.13573-1-vivek.gautam@codeaurora.org> <20190612071554.13573-4-vivek.gautam@codeaurora.org> <20190614040520.GK22737@tuxbook-pro> <3e1f5e03-6448-8730-056d-fc47bdd71b3f@codeaurora.org> <20190618175218.GH4270@fuggles.cambridge.arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20170113 (1.7.2) Cc: "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" , linux-arm-msm , Will Deacon , open list , Bjorn Andersson , David Brown , "list@263.net:IOMMU DRIVERS , Joerg Roedel , " , robh+dt , Andy Gross , Robin Murphy X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.12 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: iommu-bounces@lists.linux-foundation.org Errors-To: iommu-bounces@lists.linux-foundation.org [+Krishna] Hi Vivek, On Mon, Jun 24, 2019 at 03:58:32PM +0530, Vivek Gautam wrote: > On Tue, Jun 18, 2019 at 11:22 PM Will Deacon wrote: > > On Fri, Jun 14, 2019 at 02:48:07PM +0530, Vivek Gautam wrote: > > > On 6/14/2019 9:35 AM, Bjorn Andersson wrote: > > > > On Wed 12 Jun 00:15 PDT 2019, Vivek Gautam wrote: > > > > > diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c > > > > > index 0ad086da399c..3c3ad43eda97 100644 > > > > > --- a/drivers/iommu/arm-smmu.c > > > > > +++ b/drivers/iommu/arm-smmu.c > > > > > @@ -39,6 +39,7 @@ > > > > > #include > > > > > #include > > > > > #include > > > > > +#include > > > > > #include > > > > > #include > > > > > @@ -177,6 +178,7 @@ struct arm_smmu_device { > > > > > u32 features; > > > > > #define ARM_SMMU_OPT_SECURE_CFG_ACCESS (1 << 0) > > > > > +#define ARM_SMMU_OPT_QCOM_FW_IMPL_SAFE_ERRATA (1 << 1) > > > > > u32 options; > > > > > enum arm_smmu_arch_version version; > > > > > enum arm_smmu_implementation model; > > > > > @@ -262,6 +264,7 @@ static bool using_legacy_binding, using_generic_binding; > > > > > static struct arm_smmu_option_prop arm_smmu_options[] = { > > > > > { ARM_SMMU_OPT_SECURE_CFG_ACCESS, "calxeda,smmu-secure-config-access" }, > > > > > + { ARM_SMMU_OPT_QCOM_FW_IMPL_SAFE_ERRATA, "qcom,smmu-500-fw-impl-safe-errata" }, > > > > This should be added to the DT binding as well. > > > > > > Ah right. I missed that. Will add this and respin unless Robin and Will have > > > concerns with this change. > > > > My only concern really is whether it's safe for us to turn this off. It's > > clear that somebody went to a lot of effort to add this extra goodness to > > the IP, but your benchmarks suggest they never actually tried it out after > > they finished building it. > > > > Is there some downside I'm not seeing from disabling this stuff? > > This wait-for-safe is a TLB invalidation enhancement to help display > and camera devices. > The SMMU hardware throttles the invalidations so that clients such as > display and camera can indicate when to start the invalidation. > So the SMMU essentially reduces the rate at which invalidations are > serviced from its queue. This also throttles the invalidations from > other masters too. > > On sdm845, the software is expected to serialize the invalidation > command loading into SMMU invalidation FIFO using hardware locks > (downstream code [2]), and is also expected to throttle non-real time > clients while waiting for SAFE==1 (downstream code[2]). We don't do > any of these yet, and as per my understanding as this wait-for-safe is > enabled by the bootloader in a one time config, this logic reduces > performance of devices such as usb and ufs. > > There's isn't any downside from disabling this logic until we have all > the pieces together from downstream in upstream kernels, and until we > have sdm845 devices that are running with full display/gfx stack > running. That's when we plan to revisit this and enable all the pieces > to get display and USB/UFS working with their optimum performance. Generally, I'd agree that approaching this incrementally makes sense, but in this case you're adding new device-tree properties ("qcom,smmu-500-fw-impl-safe-errata") in order to do so, which seems questionable if they're only going to be used in the short-term and will be obsolete once Linux knows how to drive the device properly. Instead, I think this needs to be part of a separate file that is maintained by you, which follows on from the work that Krishna is doing for nvidia built on top of Robin's prototype patches: http://linux-arm.org/git?p=linux-rm.git;a=shortlog;h=refs/heads/iommu/smmu-impl Once we have that, you can key this behaviour off the compatible string rather than having to add quirk properties to reflect the transient needs of Linux. Krishna -- how have you been getting on with the branch above? Will _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu