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

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Message-ID: <29cf2c16-3a0e-42c5-a083-16f77ae5d09a@nvidia.com>
Date: Fri, 21 Nov 2025 11:21:21 +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 12/11/2025 07:21, Aaron Kling wrote:
> On Wed, Nov 12, 2025 at 12:18 AM Jon Hunter <jonathanh@...dia.com> 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
>> not merge this for v6.19 without the DT changes.
> 
> The dt changes are here [0].

To confirm, applying the DT changes do not fix this for me. Thierry is 
having a look at this to see if there is a way to fix this.

BTW, I have also noticed that Thierry's memory frequency test [0] is 
also failing on Tegra186. The test simply tries to set the frequency via 
the sysfs and this is now failing. I am seeing ...

memory: emc: - available rates: (* = current)
memory: emc:   -   40800000
memory: emc:   -   68000000
memory: emc:   -  102000000
memory: emc:   -  204000000
memory: emc:   -  408000000
memory: emc:   -  665600000
memory: emc:   -  800000000
memory: emc:   - 1062400000
memory: emc:   - 1331200000
memory: emc:   - 1600000000
memory: emc:   - 1866000000 *
memory: emc: - testing:
memory: emc:   -   40800000...OSError: [Errno 34] Numerical result out 
of range

Jon

[0] https://github.com/thierryreding/tegra-tests

-- 
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