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

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Date:   Mon, 29 May 2023 11:08:46 +0200
From:   Konrad Dybcio <konrad.dybcio@...aro.org>
To:     Dmitry Baryshkov <dmitry.baryshkov@...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 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"?

> - 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

> - 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.

Konrad
>