linux-kernel - Re: [PATCH] drm/msm/dpu: Add missing safe_lut

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Message-ID: <20231031081931.GC11778@thinkpad>
Date:   Tue, 31 Oct 2023 13:49:31 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     Bjorn Andersson <quic_bjorande@...cinc.com>
Cc:     Rob Clark <robdclark@...il.com>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Sean Paul <sean@...rly.run>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Bjorn Andersson <andersson@...nel.org>,
        Kuogee Hsieh <quic_khsieh@...cinc.com>,
        Johan Hovold <johan@...nel.org>, linux-arm-msm@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, freedreno@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Doug Anderson <dianders@...omium.org>,
        Rob Clark <robdclark@...omium.org>
Subject: Re: [PATCH] drm/msm/dpu: Add missing safe_lut_tbl in sc8280xp catalog

On Mon, Oct 30, 2023 at 04:23:20PM -0700, Bjorn Andersson wrote:
> During USB transfers on the SC8280XP __arm_smmu_tlb_sync() is seen to
> typically take 1-2ms to complete. As expected this results in poor
> performance, something that has been mitigated by proposing running the
> iommu in non-strict mode (boot with iommu.strict=0).
> 
> This turns out to be related to the SAFE logic, and programming the QOS
> SAFE values in the DPU (per suggestion from Rob and Doug) reduces the
> TLB sync time to below 10us, which means significant less time spent
> with interrupts disabled and a significant boost in throughput.
> 
> Fixes: 4a352c2fc15a ("drm/msm/dpu: Introduce SC8280XP")
> Cc: stable@...r.kernel.org
> Suggested-by: Doug Anderson <dianders@...omium.org>
> Suggested-by: Rob Clark <robdclark@...omium.org>
> Signed-off-by: Bjorn Andersson <quic_bjorande@...cinc.com>
> ---
>  drivers/gpu/drm/msm/disp/dpu1/catalog/dpu_8_0_sc8280xp.h | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/gpu/drm/msm/disp/dpu1/catalog/dpu_8_0_sc8280xp.h b/drivers/gpu/drm/msm/disp/dpu1/catalog/dpu_8_0_sc8280xp.h
> index 1ccd1edd693c..4c0528794e7a 100644
> --- a/drivers/gpu/drm/msm/disp/dpu1/catalog/dpu_8_0_sc8280xp.h
> +++ b/drivers/gpu/drm/msm/disp/dpu1/catalog/dpu_8_0_sc8280xp.h
> @@ -406,6 +406,7 @@ static const struct dpu_perf_cfg sc8280xp_perf_data = {
>  	.min_llcc_ib = 0,
>  	.min_dram_ib = 800000,
>  	.danger_lut_tbl = {0xf, 0xffff, 0x0},
> +	.safe_lut_tbl = {0xfe00, 0xfe00, 0xffff},

What does these values represent? And how SAFE is to override the default QoS
values?

I'm not too familiar with the MSM DRM driver, so please excuse my ignorance.

- Mani

>  	.qos_lut_tbl = {
>  		{.nentry = ARRAY_SIZE(sc8180x_qos_linear),
>  		.entries = sc8180x_qos_linear
> 
> ---
> base-commit: c503e3eec382ac708ee7adf874add37b77c5d312
> change-id: 20231030-sc8280xp-dpu-safe-lut-9769027b8452
> 
> Best regards,
> -- 
> Bjorn Andersson <quic_bjorande@...cinc.com>
> 

-- 
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