linux-kernel - Re: [RFC PATCH 11/12] platform/x86: skeleton for oftree based board device initialization

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Date:   Fri, 12 Feb 2021 10:58:58 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     "Enrico Weigelt, metux IT consult" <info@...ux.net>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, Hans de Goede <hdegoede@...hat.com>
Subject: Re: [RFC PATCH 11/12] platform/x86: skeleton for oftree based board
 device initialization

On Mon, Feb 8, 2021 at 11:22 PM Enrico Weigelt, metux IT consult
<info@...ux.net> wrote:

> Lots of boards have extra devices that can't be fully probed via bus'es
> (like PCI) or generic firmware mechanisms like ACPI. Often those capabilities
> are just partial or even highly depend on firmware version.

I think Intel people often take the stance that the ACPI DSDT (or whatever)
needs to be fixed.

If the usecase is to explicitly work around deployed firmware that cannot
and will not be upgraded/fixed by describing the hardware using DT
instead, based on just the DMI ID then we should spell that out
explicitly.

It feels a bit like fixing a problem using a different hardware description
just because we can. Look in drivers/gpio/gpiolib-acpi.c
table gpiolib_acpi_quirks[]. It's just an example how this is fixed using
fine granular ACPI-specific mechanisms at several places in the kernel
instead of just tossing out the whole description and redoing it in
device tree.

I haven't worked with this in practice so I suppose it is a bit up to
the people who end up having to fix this kind of stuff, Hans de Goede
and Andy are fixing this kind of stuff all the time so their buy-in is
important, we need to see that this is a real, useful tool for people
like them, not just nice to have.

Yours,
Linus Walleij