linux-kernel - Re: [PATCH v7 10/12] nvmem: s32g2_siul2: add NVMEM driver for SoC information

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Message-ID: <53bc13b9-365e-4212-84f9-85e67c23e067@oss.nxp.com>
Date: Fri, 1 Aug 2025 17:36:40 +0300
From: Andrei Stefanescu <andrei.stefanescu@....nxp.com>
To: Arnd Bergmann <arnd@...db.de>, Linus Walleij <linus.walleij@...aro.org>,
 Bartosz Golaszewski <brgl@...ev.pl>, Rob Herring <robh@...nel.org>,
 krzk+dt@...nel.org, Conor Dooley <conor+dt@...nel.org>,
 Chester Lin <chester62515@...il.com>, Matthias Brugger <mbrugger@...e.com>,
 Ghennadi Procopciuc <Ghennadi.Procopciuc@....com>,
 Larisa Grigore <larisa.grigore@....com>, Lee Jones <lee@...nel.org>,
 Shawn Guo <shawnguo@...nel.org>, Sascha Hauer <s.hauer@...gutronix.de>,
 Fabio Estevam <festevam@...il.com>, aisheng.dong@....com,
 Jacky Bai <ping.bai@....com>, Greg Kroah-Hartman
 <gregkh@...uxfoundation.org>, "Rafael J . Wysocki" <rafael@...nel.org>,
 Srinivas Kandagatla <srini@...nel.org>
Cc: "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, NXP S32 Linux Team <s32@....com>,
 Christophe Lizzi <clizzi@...hat.com>, Alberto Ruiz <aruizrui@...hat.com>,
 Enric Balletbo <eballetb@...hat.com>, echanude@...hat.com,
 Pengutronix Kernel Team <kernel@...gutronix.de>, imx@...ts.linux.dev,
 Vincent Guittot <vincent.guittot@...aro.org>
Subject: Re: [PATCH v7 10/12] nvmem: s32g2_siul2: add NVMEM driver for SoC
 information

> Thank you for the review! I've just taken a look over soc_device
> and I agree, this driver should be a soc_device. I will convert
> it in the next revision.
> 

Hi Arnd,

I took a more in-depth look over soc_device and how to apply it to SIUL2
and I have encountered an issue. Downstream [1], [2], [3] we use SIUL2
nvmem-cells to set the PCIe vendor id partially based on the part number
and also to ensure that the SerDes subsystem is present. I don't think we can
achieve this with a soc_device driver. I saw that we could export a custom
attribute but I don't think we can read it from the PCIe driver.

Apart from the proposed NVMEM driver, there is also an option of exporting
a syscon regmap for the registers which provide information about the SoC.

I have seen that typically NVMEM drivers export information read from fuses
but I think having a NVMEM driver is nicer way to access the information
instead of using a syscon regmap and manually extracting the needed bits. 

To provide a bit of context: the SIUL2 IP has two registers called
SIUL2 MCU ID Register (MIDR1/2) which export information such as:
the part number, major, minor, package, maximum frequency,
flash size, SRAM size, SerDes susbsytem presence and so on.

S32G2/3 SoCs have two SIUL2 blocks named SIUL2_0 and SIUL2_1. We need
to export the MIDR1/2 registers of both SIUL2 hardware blocks.

What do you think? Would it be ok to keep the existing NVMEM implementation?
Do you have any other suggestions?

Best regards,
Andrei

[1] - https://github.com/nxp-auto-linux/linux/blob/release/bsp44.0-6.6.85-rt/arch/arm64/boot/dts/freescale/s32cc.dtsi#L1036
[2] - https://github.com/nxp-auto-linux/linux/blob/release/bsp44.0-6.6.85-rt/drivers/pci/controller/dwc/pci-s32cc.c#L832
[3] - https://github.com/nxp-auto-linux/linux/blob/release/bsp44.0-6.6.85-rt/drivers/pci/controller/dwc/pci-s32cc.c#L163