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

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Message-ID: <74ebd488-15c1-47a5-86f4-14263e3a914e@linaro.org>
Date: Tue, 9 Apr 2024 20:27:22 +0200
From: Konrad Dybcio <konrad.dybcio@...aro.org>
To: Dmitry Baryshkov <dmitry.baryshkov@...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 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

Konrad