linux-kernel - Re: [PATCH 5/5] drm/msm/dpu1: Handle the reg bus ICC path

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Message-ID: <f77bcfdc-e50e-d27b-6634-2095033c85d6@linaro.org>
Date:   Mon, 17 Apr 2023 17:55:18 +0200
From:   Konrad Dybcio <konrad.dybcio@...aro.org>
To:     Rob Clark <robdclark@...il.com>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Krishna Manikandan <quic_mkrishn@...cinc.com>
Cc:     Marijn Suijten <marijn.suijten@...ainline.org>,
        linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/5] drm/msm/dpu1: Handle the reg bus ICC path



On 17.04.2023 17:30, Konrad Dybcio wrote:
> Apart from the already handled data bus (MAS_MDP_Pn<->DDR), there's
> another path that needs to be handled to ensure MDSS functions properly,
> namely the "reg bus", a.k.a the CPU-MDSS interconnect.
> 
> Gating that path may have a variety of effects.. from none to otherwise
> inexplicable DSI timeouts..
> 
> On the DPU side, we need to keep the bus alive. The vendor driver
> kickstarts it to max (300Mbps) throughput on first commit, but in
> exchange for some battery life in rare DPU-enabled-panel-disabled
> usecases, we can request it at DPU init and gate it at suspend.
> 
> Signed-off-by: Konrad Dybcio <konrad.dybcio@...aro.org>
> ---
[...]
> @@ -1261,6 +1270,15 @@ static int __maybe_unused dpu_runtime_resume(struct device *dev)
>  		return rc;
>  	}
>  
> +	/*
> +	 * The vendor driver supports setting 76.8 / 150 / 300 Mbps on this
This should have obviously been M>B<ps..

Konrad
> +	 * path, but it seems to go for the highest level when display output
> +	 * is enabled and zero otherwise. For simplicity, we can assume that
> +	 * DPU being enabled and running implies that.
> +	 */
> +	if (dpu_kms->reg_bus_path)
> +		icc_set_bw(dpu_kms->reg_bus_path, 0, MBps_to_icc(300));
> +
>  	dpu_vbif_init_memtypes(dpu_kms);
>  
>  	drm_for_each_encoder(encoder, ddev)
> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.h b/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.h
> index d5d9bec90705..c332381d58c4 100644
> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.h
> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.h
> @@ -111,6 +111,7 @@ struct dpu_kms {
>  	atomic_t bandwidth_ref;
>  	struct icc_path *mdp_path[2];
>  	u32 num_mdp_paths;
> +	struct icc_path *reg_bus_path;
>  };
>  
>  struct vsync_info {
>