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Message-ID: <bb8e3633-3fe5-b4d2-08e1-0789a68620a8@linaro.org>
Date:   Wed, 19 Apr 2023 23:26:21 +0200
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Subject: Re: [Freedreno] [PATCH 5/5] drm/msm/dpu1: Handle the reg bus ICC path
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To:     Jeykumar Sankaran <quic_jeykumar@quicinc.com>,
        Rob Clark <robdclark@gmail.com>,
        Abhinav Kumar <quic_abhinavk@quicinc.com>,
        Dmitry Baryshkov <dmitry.baryshkov@linaro.org>,
        Sean Paul <sean@poorly.run>, David Airlie <airlied@gmail.com>,
        Daniel Vetter <daniel@ffwll.ch>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Krishna Manikandan <quic_mkrishn@quicinc.com>
Cc:     devicetree@vger.kernel.org, linux-arm-msm@vger.kernel.org,
        linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org,
        Marijn Suijten <marijn.suijten@somainline.org>,
        freedreno@lists.freedesktop.org
References: <20230417-topic-dpu_regbus-v1-0-06fbdc1643c0@linaro.org>
 <20230417-topic-dpu_regbus-v1-5-06fbdc1643c0@linaro.org>
 <11c72462-b256-d0db-a666-9615da4420f6@quicinc.com>
 <e15ec005-ef52-c14c-bdeb-faaca207d39b@linaro.org>
 <77bb1b3c-09cb-310a-be34-166e573a13a7@quicinc.com>
From:   Konrad Dybcio <konrad.dybcio@linaro.org>
In-Reply-To: <77bb1b3c-09cb-310a-be34-166e573a13a7@quicinc.com>
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Precedence: bulk


On 19.04.2023 22:11, Jeykumar Sankaran wrote:
> 
> 
> On 4/19/2023 12:48 PM, Konrad Dybcio wrote:
>>
>>
>> On 19.04.2023 21:06, Jeykumar Sankaran wrote:
>>>
>>>
>>> On 4/17/2023 8:30 AM, 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@linaro.org>
>>>> ---
>>>>    drivers/gpu/drm/msm/disp/dpu1/dpu_kms.c | 22 ++++++++++++++++++++--
>>>>    drivers/gpu/drm/msm/disp/dpu1/dpu_kms.h |  1 +
>>>>    2 files changed, 21 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.c
>>>> index dd6c1c40ab9e..d1f77faebbc0 100644
>>>> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.c
>>>> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.c
>>>> @@ -384,15 +384,17 @@ static int dpu_kms_global_obj_init(struct dpu_kms *dpu_kms)
>>>>        return 0;
>>>>    }
>>>>    -static int dpu_kms_parse_data_bus_icc_path(struct dpu_kms *dpu_kms)
>>>> +static int dpu_kms_parse_icc_paths(struct dpu_kms *dpu_kms)
>>>>    {
>>>>        struct icc_path *path0;
>>>>        struct icc_path *path1;
>>>> +    struct icc_path *reg_bus_path;
>>>>        struct drm_device *dev = dpu_kms->dev;
>>>>        struct device *dpu_dev = dev->dev;
>>>>          path0 = msm_icc_get(dpu_dev, "mdp0-mem");
>>>>        path1 = msm_icc_get(dpu_dev, "mdp1-mem");
>>>> +    reg_bus_path = msm_icc_get(dpu_dev, "cpu-cfg");
>>>>          if (IS_ERR_OR_NULL(path0))
>>>>            return PTR_ERR_OR_ZERO(path0);
>>>> @@ -404,6 +406,10 @@ static int dpu_kms_parse_data_bus_icc_path(struct dpu_kms *dpu_kms)
>>>>            dpu_kms->mdp_path[1] = path1;
>>>>            dpu_kms->num_mdp_paths++;
>>>>        }
>>>> +
>>>> +    if (!IS_ERR_OR_NULL(reg_bus_path))
>>>> +        dpu_kms->reg_bus_path = reg_bus_path;
>>>> +
>>>>        return 0;
>>>>    }
>>>>    @@ -1039,7 +1045,7 @@ static int dpu_kms_hw_init(struct msm_kms *kms)
>>>>            DPU_DEBUG("REG_DMA is not defined");
>>>>        }
>>>>    -    dpu_kms_parse_data_bus_icc_path(dpu_kms);
>>>> +    dpu_kms_parse_icc_paths(dpu_kms);
>>>>          rc = pm_runtime_resume_and_get(&dpu_kms->pdev->dev);
>>>>        if (rc < 0)
>>>> @@ -1241,6 +1247,9 @@ static int __maybe_unused dpu_runtime_suspend(struct device *dev)
>>>>        for (i = 0; i < dpu_kms->num_mdp_paths; i++)
>>>>            icc_set_bw(dpu_kms->mdp_path[i], 0, 0);
>>>>    +    if (dpu_kms->reg_bus_path)
>>>> +        icc_set_bw(dpu_kms->reg_bus_path, 0, 0);
>>>> +
>>>>        return 0;
>>>>    }
>>>>    @@ -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
>>> How do you arrive at these distint BW values? Are they provided by the ICC fwk for the given path?
>> They're hardcoded in the SDE driver.
>>
>> Konrad
> These bandwidths are derived from the scaling frequencies of all the buses participating in the icc-path. So they cannot be constants. Ideally they should be read from the hw catalog data of the respective platform.
msm-5.4 : rotator/sde_rotator_base.c

static const struct sde_rot_bus_data sde_rot_reg_bus_table[] = {
        {0, 0},
        {0, 76800},
        {0, 150000},
        {0, 300000},
};

One of the two voters begs to disagree, but I do indeed see that some
SoCs (lahaina, yupik, shima..) cast votes for 74/148/265 MBps instead
of 77/150/300 from the MDSS device (with rotator being considered
separate), or so say their DTs, thanks for pointing that out.

Nonetheless, this code would taste good with bolognese sauce..

Konrad

> 
> Jeykumar S.
>>>> +     * 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 {
>>>>