Re: [PATCH v2 1/2] EDAC: add EDAC driver for DMC520

From: James Morse
Date: Mon Mar 25 2019 - 14:28:00 EST

Hi guys,

On 23/03/2019 09:23, Borislav Petkov wrote:
> On Thu, Mar 07, 2019 at 01:24:01AM +0000, Rui Zhao wrote:
>> From: Rui Zhao <ruizhao@xxxxxxxxxxxxx>
>> New driver supports error detection and correction on
>> the devices with ARM DMC-520 memory controller.

A question/suggestion on the direction...

Could we avoid probing the driver based on the root hardware compatible?
Could we use the device/chip/platform specific one instead?

We want to avoid per-function edac drivers. If ${my_chip} has edac support for L3 and
memory, I should have a ${my_chip}_edac driver that pulls in the appropriate L3 and memory
code, and presents a sensible view to edac_core.

Thinking out loud...

You have:

>> +static const struct of_device_id dmc520_edac_driver_id[] = {
>> + { .compatible = "arm,dmc-520", },
>> + { /* end of table */ }
>> +};
>> +

If you wanted to add another device with edac support, we'd ask you to create
${your_chip}_edac driver and pull in the DMC520 and the other device.

But probing the 'arm,dmc-520' compatible like this leaves us in a tricky place if someone
else does this: ${their_device} probes the dmc520 like this too, but they can't stop it on
their platform as it will break yours...

It's normal to have a specific compatible, vexpress has:
| compatible = "arm,vexpress,v2f-2xv6,ca7x3", "arm,vexpress,v2f-2xv6", "arm,vexpress";

Could we do the same here:
| compatible = "vendor,soc-name-dmc520", "arm,dmc-520";

or even:
| compatible = "microsoft,product-name-dmc520", "arm,dmc-520";
if there is some firmware/board configuration that means vendor/soc isn't precise enough.

Then we always probe the driver from "vendor,soc-name-dmc520", never from "arm,dmc520".

This means we grow a list of vendor/soc-name that are using this driver, but if one of
them wants to support a second edac device, we can remove their vendor/soc-name from the
list without affecting anyone else.