linux-kernel - Re: [PATCHv7 0/3] QCOM smmu-500 wait-for-safe handling for sdm845

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Date:   Fri, 1 Nov 2019 16:31:36 +0000
From:   Will Deacon <will@...nel.org>
To:     Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>,
        agross@...nel.org
Cc:     Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>,
        iommu@...ts.linux-foundation.org,
        Stephen Boyd <swboyd@...omium.org>,
        Vivek Gautam <vivek.gautam@...eaurora.org>,
        bjorn.andersson@...aro.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Rajendra Nayak <rnayak@...eaurora.org>
Subject: Re: [PATCHv7 0/3] QCOM smmu-500 wait-for-safe handling for sdm845

On Fri, Sep 20, 2019 at 01:34:26PM +0530, Sai Prakash Ranjan wrote:
> Previous version of the patches are at [1]:
> 
> QCOM's implementation of smmu-500 on sdm845 adds a hardware logic called
> wait-for-safe. This logic helps in meeting the invalidation requirements
> from 'real-time clients', such as display and camera. This wait-for-safe
> logic ensures that the invalidations happen after getting an ack from these
> devices.
> In this patch-series we are disabling this wait-for-safe logic from the
> arm-smmu driver's probe as with this enabled the hardware tries to
> throttle invalidations from 'non-real-time clients', such as USB and UFS.
> 
> For detailed information please refer to patch [3/4] in this series.
> I have included the device tree patch too in this series for someone who
> would like to test out this. Here's a branch [2] that gets display on MTP
> SDM845 device.
> 
> This patch series is inspired from downstream work to handle under-performance
> issues on real-time clients on sdm845. In downstream we add separate page table
> ops to handle TLB maintenance and toggle wait-for-safe in tlb_sync call so that
> achieve required performance for display and camera [3, 4].

What's the plan for getting this merged? I'm not happy taking the firmware
bits without Andy's ack, but I also think the SMMU changes should go via
the IOMMU tree to avoid conflicts.

Andy?

Will