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

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Date: Tue, 9 Apr 2024 21:04:43 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Rob Clark <robdclark@...il.com>
Cc: Konrad Dybcio <konrad.dybcio@...aro.org>, 
	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 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.

> 
> BR,
> -R
> 
> >
> > >
> > > >
> > > > If that's not the case, I think the commit should be expanded with
> > > > actually setting default_speedbin for the existing GPUs.
> > >
> > > I think that should be addressed, although separately.
> >
> > I'd prefer to have it as a part of this patch, but I'd not NAK it just
> > for this reason.
> >
> > --
> > With best wishes
> > Dmitry

-- 
With best wishes
Dmitry