linux-kernel - Re: [PATCH 3/6] drm/msm/adreno: Allow specifying default speedbin value

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Date: Tue, 9 Apr 2024 21:31:11 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Konrad Dybcio <konrad.dybcio@...aro.org>
Cc: Rob Clark <robdclark@...il.com>, Bjorn Andersson <andersson@...nel.org>, 
	Abhinav Kumar <quic_abhinavk@...cinc.com>, Sean Paul <sean@...rly.run>, 
	Marijn Suijten <marijn.suijten@...ainline.org>, David Airlie <airlied@...il.com>, 
	Daniel Vetter <daniel@...ll.ch>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, linux-arm-msm@...r.kernel.org, 
	linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org, 
	freedreno@...ts.freedesktop.org, devicetree@...r.kernel.org, 
	Neil Armstrong <neil.armstrong@...aro.org>
Subject: Re: [PATCH 3/6] drm/msm/adreno: Allow specifying default speedbin value

On Tue, 9 Apr 2024 at 21:27, Konrad Dybcio <konrad.dybcio@...aro.org> wrote:
>
>
>
> On 4/9/24 20:15, Dmitry Baryshkov wrote:
> > On Tue, Apr 09, 2024 at 08:07:56PM +0200, Konrad Dybcio wrote:
> >>
> >>
> >> On 4/9/24 20:04, Dmitry Baryshkov wrote:
> >>> On Tue, Apr 09, 2024 at 10:12:00AM -0700, Rob Clark wrote:
> >>>> On Tue, Apr 9, 2024 at 8:23 AM Dmitry Baryshkov
> >>>> <dmitry.baryshkov@...aro.org> wrote:
> >>>>>
> >>>>> On Tue, Apr 09, 2024 at 05:12:46PM +0200, Konrad Dybcio wrote:
> >>>>>>
> >>>>>>
> >>>>>> On 4/6/24 04:56, Dmitry Baryshkov wrote:
> >>>>>>> On Fri, Apr 05, 2024 at 10:41:31AM +0200, Konrad Dybcio wrote:
> >>>>>>>> From: Neil Armstrong <neil.armstrong@...aro.org>
> >>>>>>>>
> >>>>>>>> Usually, speedbin 0 is the "super SKU", a.k.a the one which can clock
> >>>>>>>> the highest. Falling back to it when things go wrong is largely
> >>>>>>>> suboptimal, as more often than not, the top frequencies are not
> >>>>>>>> supposed to work on other bins.
> >>>>>>>
> >>>>>>> Isn't it better to just return an error here instead of trying to guess
> >>>>>>> which speedbin to use?
> >>>>>>
> >>>>>> Not sure. I'd rather better compatibility for e.g. booting up a new
> >>>>>> laptop with just dt.
> >>>>>
> >>>>> New speedbin can have lower max speed, so by attempting to run it at
> >>>>> higher freq you might be breaking it.
> >>>>
> >>>> Usually there are some OPPs in common to all speedbins, so picking a
> >>>> freq from that set would seem like the safe thing to do
> >>>
> >>> Well, the issue is about an uknown speed bin. So in theory we know
> >>> nothing about the set of speeds itsupports. My point is that we should
> >>> simplfy fail in such case.
> >>
> >> Or we could allow e.g. the lowest frequency (or 2) which if often shared
> >> across the board to work, giving a compromise between OOBE and sanity
> >
> > That's also an option. But we should not be using existing speed table for
> > the unknown bin.
>
> I derived this logic from msm-5.15 where it's "intended behavior".. I
> suppose we can do better as you said though
>
> There have been cases in the past where the default speed bin ended up
> having a higher max freq than subsequent ones, and I don't think I can
> trust this product/feature code approach to guarantee this never
> happening again.
>
> So. I think sticking to a single lowest freq and printing a big red line
> in dmesg makes sense here

Make 0x80 the default supported-hw, make sure that the lowest freq has
0xff. Plus big-red-line.
And hope that we'll never see 16 speed bins for the hardware.


-- 
With best wishes
Dmitry