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

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Message-ID: <aaf2cc37-b8d1-4666-9a3c-753ed34af760@kernel.org>
Date: Wed, 12 Nov 2025 12:42:33 +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 11:59, Jon Hunter wrote:
> 
> On 12/11/2025 07:26, Krzysztof Kozlowski wrote:
>> 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.
> 
> Yes indeed.


Please test if dropping sync_state from memory controller drivers helps
you. This might be the easiest fix and it is also known solution when
there are no users.

Best regards,
Krzysztof