linux-kernel - Re: [PATCH v4 3/5] memory: tegra186-emc: Support non-bpmp icc scaling

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Message-ID: <6904a858-d7a3-457b-8141-692238d01582@kernel.org>
Date: Wed, 12 Nov 2025 08:26:33 +0100
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Jon Hunter <jonathanh@...dia.com>, Aaron Kling <webgeek1234@...il.com>
Cc: Rob Herring <robh@...nel.org>, Conor Dooley <conor+dt@...nel.org>,
 Thierry Reding <thierry.reding@...il.com>, linux-kernel@...r.kernel.org,
 devicetree@...r.kernel.org, linux-tegra@...r.kernel.org
Subject: Re: [PATCH v4 3/5] memory: tegra186-emc: Support non-bpmp icc scaling

On 12/11/2025 07:18, Jon Hunter wrote:
> 
> On 11/11/2025 23:17, Aaron Kling wrote:
> 
> ...
> 
>> Alright, I think I've got the picture of what's going on now. The
>> standard arm64 defconfig enables the t194 pcie driver as a module. And
>> my simple busybox ramdisk that I use for mainline regression testing
>> isn't loading any modules. If I set the pcie driver to built-in, I
>> replicate the issue. And I don't see the issue on my normal use case,
>> because I have the dt changes as well.
>>
>> So it appears that the pcie driver submits icc bandwidth. And without
>> cpufreq submitting bandwidth as well, the emc driver gets a very low
>> number and thus sets a very low emc freq. The question becomes... what
>> to do about it? If the related dt changes were submitted to
>> linux-next, everything should fall into place. And I'm not sure where
>> this falls on the severity scale since it doesn't full out break boot
>> or prevent operation.
> 
> Where are the related DT changes? If we can get these into -next and 
> lined up to be merged for v6.19, then that is fine. However, we should 

It's still breaking all the users then.

> not merge this for v6.19 without the DT changes.
> 
> I will also talk with Thierry to see if he has any concerns about users 
> seeing slow performance if they don't have an up-to-date DTB.
> 
> Is there any easy way to detect if the DTB has he necessary properties 
> to enable ICC scaling?
> 
> Jon
> 


Best regards,
Krzysztof