linux-kernel - Re: [PATCH v3 2/3] firmware: add exynos ACPM protocol driver

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Message-ID: <0ba62a72-8247-447f-b710-234385a29d14@gmail.com>
Date: Sun, 8 Dec 2024 18:38:50 +0200
From: Markuss Broks <markuss.broks@...il.com>
To: Daniel Lezcano <daniel.lezcano@...aro.org>,
 Krzysztof Kozlowski <krzk@...nel.org>
Cc: Tudor Ambarus <tudor.ambarus@...aro.org>, robh@...nel.org,
 krzk+dt@...nel.org, conor+dt@...nel.org, alim.akhtar@...sung.com,
 linux-kernel@...r.kernel.org, linux-samsung-soc@...r.kernel.org,
 devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 andre.draszik@...aro.org, kernel-team@...roid.com, willmcvicker@...gle.com,
 peter.griffin@...aro.org, javierm@...hat.com, tzimmermann@...e.de,
 vincent.guittot@...aro.org, ulf.hansson@...aro.org, arnd@...db.de
Subject: Re: [PATCH v3 2/3] firmware: add exynos ACPM protocol driver


On 12/6/24 9:50 PM, Daniel Lezcano wrote:
> On 12/6/24 14:28, Krzysztof Kozlowski wrote:
>> On Fri, Dec 06, 2024 at 12:39:56AM +0100, Daniel Lezcano wrote:
>>>> +# SPDX-License-Identifier: GPL-2.0-only
>>>> +
>>>> +config EXYNOS_ACPM_PROTOCOL
>>>> +    tristate "Exynos Alive Clock and Power Manager (ACPM) Message 
>>>> Protocol"
>>>
>>> Given the importance of this driver where a lot of PM services rely 
>>> on, does
>>> it really make sense to allow it as a module ?
>>>
>>> Some PM services may be needed very early in the boot process
>>>
>>
>> If it works as module e.g. on Android, it is beneficial. I think the
>> platform was booting fine without it, at least to some shell, so I can
>> imagine this can be loaded a bit later.
>
> Usually the firmware sets the frequency to the maximum in order to 
> boot the kernel as fast as possible. That may lead to thermal issues 
> at boot time where the thermal framework won't be able to kick in as 
> some components will depends on ACPM while the system stays at its 
> highest performance state.
Also, as far as I understand, ACPM is used here as an interface to the 
PMIC, so every driver which would need power management from the main 
SoC PMIC would get deferred until the ACPM module has been loaded. This 
would make it impossible to e.g. initialize the UFS or the MMC card 
before initramfs.
>
>
- Markuss