linux-kernel - Re: [PATCH] drm/msm/a6xx: Fix speed-bin detection vs probe-defer

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Message-ID: <61b0954d-d294-4c60-3188-aa29b6545465@quicinc.com>
Date:   Tue, 15 Nov 2022 02:03:19 +0530
From:   Akhil P Oommen <quic_akhilpo@...cinc.com>
To:     Doug Anderson <dianders@...omium.org>,
        Rob Clark <robdclark@...il.com>
CC:     <dri-devel@...ts.freedesktop.org>,
        <freedreno@...ts.freedesktop.org>, <linux-arm-msm@...r.kernel.org>,
        Rob Clark <robdclark@...omium.org>,
        "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>, Chia-I Wu <olvaffe@...il.com>,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/msm/a6xx: Fix speed-bin detection vs probe-defer

On 11/15/2022 1:57 AM, Doug Anderson wrote:
> Hi,
>
> On Mon, Nov 14, 2022 at 11:41 AM Rob Clark <robdclark@...il.com> wrote:
>> From: Rob Clark <robdclark@...omium.org>
>>
>> If we get an error (other than -ENOENT) we need to propagate that up the
>> stack.  Otherwise if the nvmem driver hasn't probed yet, we'll end up with
>> whatever OPP(s) are represented by bit zero.
> Can you explain the "whatever OPP(s) are represented by bit zero"
> part? This doesn't seem to be true because `supp_hw` is initiated to
> UINT_MAX. If I'm remembering how this all works, doesn't that mean
> that if we get an error we'll assume all OPPs are OK?
>
> I'm not saying that I'm against your change, but I think maybe you're
> misdescribing the old behavior.
>
> Speaking of the initialization of supp_hw, if we want to change the
> behavior like your patch does then we should be able to remove that
> initialization, right?
>
> I would also suspect that your patch will result in a compiler
> warning, at least on some compilers. The goto label `done` is no
> longer needed, right?
>
> -Doug
You are right about the commit message. The problem is we can't enable 
all bits in supp_hw anymore due to changes like this:
https://patchwork.kernel.org/project/linux-arm-msm/patch/20220829011035.1.Ie3564662150e038571b7e2779cac7229191cf3bf@changeid/

This creates 2 opps with same freq when supp_hw = UINT_MAX.

-Akhil.