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

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Message-ID: <CAF6AEGtshehnG8vPonD=ckH8-xbW+D6ykCrZBWDT6bVh3U0pOw@mail.gmail.com>
Date:   Mon, 14 Nov 2022 12:42:41 -0800
From:   Rob Clark <robdclark@...il.com>
To:     Doug Anderson <dianders@...omium.org>
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>,
        Akhil P Oommen <quic_akhilpo@...cinc.com>,
        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 Mon, Nov 14, 2022 at 12:27 PM Doug Anderson <dianders@...omium.org> 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?

Oh, that's right.. and even worse!  Ok, stand by for v2

> 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