linux-kernel - Re: [PATCH 0/8] Support dynamic EMC frequency scaling on Tegra186/Tegra194

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Message-ID: <55e28e33-5a9d-4528-a44b-87cdf66bc289@nvidia.com>
Date: Fri, 5 Sep 2025 19:07:02 +0530
From: Sumit Gupta <sumitg@...dia.com>
To: Aaron Kling <webgeek1234@...il.com>
Cc: Krzysztof Kozlowski <krzk@...nel.org>, Rob Herring <robh@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, Thierry Reding
 <thierry.reding@...il.com>, Jonathan Hunter <jonathanh@...dia.com>,
 "Rafael J. Wysocki" <rafael@...nel.org>,
 Viresh Kumar <viresh.kumar@...aro.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, bbasu@...dia.com,
 linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
 linux-tegra@...r.kernel.org, linux-pm@...r.kernel.org, sumitg@...dia.com
Subject: Re: [PATCH 0/8] Support dynamic EMC frequency scaling on
 Tegra186/Tegra194

On 04/09/25 22:17, Aaron Kling wrote:
> External email: Use caution opening links or attachments
>
>
> On Thu, Sep 4, 2025 at 6:47 AM Sumit Gupta <sumitg@...dia.com> wrote:
>>
>> On 01/09/25 09:03, Aaron Kling via B4 Relay wrote:
>>> External email: Use caution opening links or attachments
>>>
>>>
>>> This series borrows the concept used on Tegra234 to scale EMC based on
>>> CPU frequency and applies it to Tegra186 and Tegra194. Except that the
>>> bpmp on those archs does not support bandwidth manager, so the scaling
>>> iteself is handled similar to how Tegra124 currently works.
>>>
>>> Signed-off-by: Aaron Kling <webgeek1234@...il.com>
>>> ---
>> Tegra186/194 had multiple drivers for BWMGR, ISOMGR and LA+PTSA configs
>> on the CPU side. I am not sure how effective this patch series will be
>> in absence
>> of those components. In Tegra234, those were moved to BPMP-FW. So, Kernel
>> forwards the BW request to BPMP (R5) who takes care of setting the final
>> freq.
> I know it's not ideal, but it seems to be working okay as a rough
> approximation. When the cpu governor kicks up the cpu freq, the emc
> freq scales to match. In my testing, this has been enough to keep aosp
> from obviously lagging. Existing drivers for earlier archs, such as
> tegra124-emc, stub out LA+PTSA as well. Does the lack of that handling
> make things worse for Tegra186/194 than it would for
> Tegra124/Tegra210? I'm trying to improve things across all these archs
> small pieces at time. In several of my recent series, I'm just trying
> to get any form of load based dfs to work, so I don't have to keep
> everything pegged to max frequency with the associated thermals and
> power usage.
>
> Aaron

I am not much familiar with the previous SoCs. But yes having some kind
of scaling is better than not having at all and running always at max. This
can be a starting point of more improvements for these SoCs in future.

Thank you,
Sumit Gupta