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

[Andrei Stefanescu]

> 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