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

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Message-ID: <d16803e5-7b6d-4472-b50c-aa324cf52736@nvidia.com>
Date: Wed, 12 Nov 2025 06:18:08 +0000
From: Jon Hunter <jonathanh@...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>, 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 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 
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

-- 
nvpublic