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

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Date: Tue, 9 Apr 2024 21:15:00 +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, 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.

-- 
With best wishes
Dmitry