Re: [PATCHv7 3/3] iommu: arm-smmu-impl: Add sdm845 implementation hook

From: Stephen Boyd <swboyd@chromium.org>
To: Andy Gross <agross@kernel.org>, Joerg Roedel <joro@8bytes.org>,
	Robin Murphy <robin.murphy@arm.com>,
	Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>,
	Vivek Gautam <vivek.gautam@codeaurora.org>,
	Will Deacon <will@kernel.org>,
	bjorn.andersson@linaro.org, iommu@lists.linux-foundation.org
Cc: linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org,
	Rajendra Nayak <rnayak@codeaurora.org>,
	Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
Subject: Re: [PATCHv7 3/3] iommu: arm-smmu-impl: Add sdm845 implementation hook
Date: Fri, 20 Sep 2019 14:07:28 -0700	[thread overview]
Message-ID: <5d853f91.1c69fb81.a630b.98dd@mx.google.com> (raw)
In-Reply-To: <3ed0de38b57fda1995d0f231cbcec38c16387a2a.1568966170.git.saiprakash.ranjan@codeaurora.org>

Quoting Sai Prakash Ranjan (2019-09-20 01:04:29)
> From: Vivek Gautam <vivek.gautam@codeaurora.org>
> 
> Add reset hook for sdm845 based platforms to turn off
> the wait-for-safe sequence.
> 
> Understanding how wait-for-safe logic affects USB and UFS performance
> on MTP845 and DB845 boards:
> 
> Qcom's implementation of arm,mmu-500 adds a WAIT-FOR-SAFE logic
> to address under-performance issues in real-time clients, such as
> Display, and Camera.
> On receiving an invalidation requests, the SMMU forwards SAFE request
> to these clients and waits for SAFE ack signal from real-time clients.
> The SAFE signal from such clients is used to qualify the start of
> invalidation.
> This logic is controlled by chicken bits, one for each - MDP (display),
> IFE0, and IFE1 (camera), that can be accessed only from secure software
> on sdm845.
> 
> This configuration, however, degrades the performance of non-real time
> clients, such as USB, and UFS etc. This happens because, with wait-for-safe
> logic enabled the hardware tries to throttle non-real time clients while
> waiting for SAFE ack signals from real-time clients.
> 
> On mtp845 and db845 devices, with wait-for-safe logic enabled by the
> bootloaders we see degraded performance of USB and UFS when kernel
> enables the smmu stage-1 translations for these clients.
> Turn off this wait-for-safe logic from the kernel gets us back the perf
> of USB and UFS devices until we re-visit this when we start seeing perf
> issues on display/camera on upstream supported SDM845 platforms.
> The bootloaders on these boards implement secure monitor callbacks to
> handle a specific command - QCOM_SCM_SVC_SMMU_PROGRAM with which the
> logic can be toggled.
> 
> There are other boards such as cheza whose bootloaders don't enable this
> logic. Such boards don't implement callbacks to handle the specific SCM
> call so disabling this logic for such boards will be a no-op.
> 
> This change is inspired by the downstream change from Patrick Daly
> to address performance issues with display and camera by handling
> this wait-for-safe within separte io-pagetable ops to do TLB
> maintenance. So a big thanks to him for the change and for all the
> offline discussions.
> 
> Without this change the UFS reads are pretty slow:
> $ time dd if=/dev/sda of=/dev/zero bs=1048576 count=10 conv=sync
> 10+0 records in
> 10+0 records out
> 10485760 bytes (10.0MB) copied, 22.394903 seconds, 457.2KB/s
> real    0m 22.39s
> user    0m 0.00s
> sys     0m 0.01s
> 
> With this change they are back to rock!
> $ time dd if=/dev/sda of=/dev/zero bs=1048576 count=300 conv=sync
> 300+0 records in
> 300+0 records out
> 314572800 bytes (300.0MB) copied, 1.030541 seconds, 291.1MB/s
> real    0m 1.03s
> user    0m 0.00s
> sys     0m 0.54s
> 
> Signed-off-by: Vivek Gautam <vivek.gautam@codeaurora.org>
> Reviewed-by: Robin Murphy <robin.murphy@arm.com>
> Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
> ---

Reviewed-by: Stephen Boyd <swboyd@chromium.org>