linux-kernel - Re: [RFC PATCH] gpio: support for GPIO forwarding

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Date:	Wed, 4 Feb 2015 10:51:27 +0100
From:	Linus Walleij <linus.walleij@...aro.org>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	Alexandre Courbot <gnurou@...il.com>,
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Darren Hart <dvhart@...ux.intel.com>,
	Arnd Bergmann <arnd@...db.de>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>
Subject: Re: [RFC PATCH] gpio: support for GPIO forwarding

On Fri, Jan 30, 2015 at 5:17 PM, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> On Friday, January 30, 2015 03:48:30 PM Linus Walleij wrote:

>> So you could detect one by making a checksum of the binary or something.
>>
>> And then you'd know that the table with this checksum needs patching?
>
> At a single table level it is generally difficult to say whether or not
> things are going to work.
>
> What needs to work is the namespace which is built from all of the tables
> provided combined.  So the namespace needs to be populated first and then
> fixes applied on top of that (presumably by deleting, adding or replacing
> objects).
>
> Now, in theory, you *may* be able to figure out that combination of tables
> A produces namespace B which then will require fix X if the system is Y,
> but quite frankly I wouldn't count on that.
>
> Moreover, fixups (or "patches" as I called them, but that wasn't exactly
> correct) need to be provided in the form of AML definition blocks to apply on
> top of an already populated namespace and if you want to use a binary kernel image,
> you can't really afford putting all that stuff for all systems it can possibly
> run on into it.  This means that distros need to be able to combine a fixup for
> the ACPI tables with the binary kernel and install the result into the system's
> boot medium (whatever it is).  Also it should be possible to update the fixup
> and the kernel image separately if necessary.
>
> Now from the kernel's perspective that raises the question: "What if the
> ACPI tables fixup provided by the distro is not sufficient?"
>
> That needs to be addressed somehow in the code.

Yeah I guess I'm convinced that we need to handle this particular
weirdness in the gpio-acpi code... if it can be contained there as
expressed by Alexandre.

Yours,
Linus Walleij
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