linux-kernel - Re: [PATCH 0/5] MDSS reg bus interconnect

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Message-ID: <3b5b6271-9611-9884-f0de-5b3f7c3d7b72@linaro.org>
Date:   Mon, 29 May 2023 13:01:13 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Konrad Dybcio <konrad.dybcio@...aro.org>
Cc:     Rob Clark <robdclark@...il.com>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        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>,
        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 0/5] MDSS reg bus interconnect

On 29/05/2023 12:08, Konrad Dybcio wrote:
> 
> 
> On 29.05.2023 10:47, Dmitry Baryshkov wrote:
>> On 29/05/2023 10:42, Konrad Dybcio wrote:
>>>
>>>
>>> On 29.05.2023 04:42, Dmitry Baryshkov wrote:
>>>> On Mon, 17 Apr 2023 at 18:30, Konrad Dybcio <konrad.dybcio@...aro.org> 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..
>>>>>
>>>>> This series tries to address the lack of that.
>>>>>
>>>>> Example path:
>>>>>
>>>>> interconnects = <&bimc MASTER_AMPSS_M0 0 &config_noc SLAVE_DISPLAY_CFG 0>;
>>>>
>>>> If we are going to touch the MDSS interconnects, could you please also
>>>> add the rotator interconnect to the bindings?
>>>> We do not need to touch it at this time, but let's not have to change
>>>> bindings later again.
>>>>
>>> Ack
>>
>> Also, several points noted from the mdss fbdev driver:
>>
>> - All possible clents vote for the low bw setting. This includes DSI, HDMI, MDSS itself and INTF
> As in, "you need NUM_CLIENTS * MIN_VOTE" or as in "any client necessitates
> a vote"?

Each client has separate vote

> 
>> - SMMU also casts such vote, which I do not think should be necessary, unless there is a separate MDSS SMMU?
> There's one on 8996, pre-845 SoCs often have a MMSS MMU, 845 and
> later have a MMSS-specific TBU which (theoretically) requires a
> vote for access to 0x400-0x7ff SIDs

Ack.

> 
>> - PINGPONG cacsts high bw setting for the sake of speeding up the LUT tables if required.
> Hm, I think is would be a separate topic.

I think so. I'd do a single vote from mdp5/dpu1. Then we can cast higher 
vote from PP/DSPP/etc.

-- 
With best wishes
Dmitry