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

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Message-ID: <c1a16ab4-72d9-f736-065c-b80858f85b7b@arm.com>
Date:   Mon, 25 Mar 2019 18:27:52 +0000
From:   James Morse <james.morse@....com>
To:     Borislav Petkov <bp@...en8.de>, Rui Zhao <ruizhao@...look.com>
Cc:     "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
        "okaya@...nel.org" <okaya@...nel.org>,
        "mchehab@...nel.org" <mchehab@...nel.org>,
        "will.deacon@....com" <will.deacon@....com>,
        "sashal@...nel.org" <sashal@...nel.org>,
        "hangl@...rosoft.com" <hangl@...rosoft.com>,
        "lewan@...rosoft.com" <lewan@...rosoft.com>,
        Rui Zhao <ruizhao@...rosoft.com>
Subject: Re: [PATCH v2 1/2] EDAC: add EDAC driver for DMC520

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@...rosoft.com>
>>
>> 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.

Thanks,

James