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Message-ID: <c547e19c-158a-4512-b2d9-01668b7ac2f0@linaro.org>
Date: Wed, 10 Apr 2024 13:47:00 +0200
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Subject: Re: [PATCH 3/6] drm/msm/adreno: Allow specifying default speedbin
 value
To: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Cc: Rob Clark <robdclark@gmail.com>, Bjorn Andersson <andersson@kernel.org>,
 Abhinav Kumar <quic_abhinavk@quicinc.com>, Sean Paul <sean@poorly.run>,
 Marijn Suijten <marijn.suijten@somainline.org>,
 David Airlie <airlied@gmail.com>, Daniel Vetter <daniel@ffwll.ch>,
 Rob Herring <robh@kernel.org>, Krzysztof Kozlowski <krzk+dt@kernel.org>,
 Conor Dooley <conor+dt@kernel.org>, linux-arm-msm@vger.kernel.org,
 linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org,
 freedreno@lists.freedesktop.org, devicetree@vger.kernel.org,
 Neil Armstrong <neil.armstrong@linaro.org>
References: <20240405-topic-smem_speedbin-v1-0-ce2b864251b1@linaro.org>
 <20240405-topic-smem_speedbin-v1-3-ce2b864251b1@linaro.org>
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From: Konrad Dybcio <konrad.dybcio@linaro.org>
In-Reply-To: <CAA8EJprAcBDEwYeGJZ=JX2qkS4wQEraXsgCiCyZU3z1ksuxivw@mail.gmail.com>
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On 4/9/24 20:31, Dmitry Baryshkov wrote:
> On Tue, 9 Apr 2024 at 21:27, Konrad Dybcio <konrad.dybcio@linaro.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@linaro.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@linaro.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.

opp-supported-hw is a u32 bitmask fwiw

I was thinking, either 0xffffffff or some driver-side hackery
(dev_pm_opp_enable).

Perhaps I'd be more in favor of the latter, as putting meaningless gobblygoo
in dt is not good

Konrad