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

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Message-ID: <4006695.qV8Mor20ru@vostro.rjw.lan>
Date:	Thu, 22 Jan 2015 17:12:07 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Linus Walleij <linus.walleij@...aro.org>
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 Thursday, January 22, 2015 09:17:38 AM Linus Walleij wrote:
> On Tue, Jan 20, 2015 at 10:25 PM, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> 
> > Yes, it can (in principle).  In fact, we have a plan to refine it, but it is
> > going to take some time.  Once we've done that, we'll see how painful it is to
> > "patch" ACPI tables this way in practice.
> >
> > Also there is an ecosystem problem related to distributing such "patches".
> > Today, distributions don't need to worry about patching buggy platform
> > firmware, because they get workarounds in the kernel, but if we switch over
> > to the model in which platform firmware "overlays" need to be provided in
> > addition to it, then suddenly questions arise about who should be responsible
> > for making them available, how to avoid duplication of efforts between
> > distributions etc.
> >
> > All of that needs to be clarified before we start making hard statements like
> > "No in-kernel workarounds for that!"
> 
> OK so why can't the patching happen in the kernel?
> 
> If the kernel anyway has to supply some kind of workaround for
> the issue, it is more a question of where to place it. Whether it does
> so by patching the ACPI tables or by detecting a bad ACPI thing
> and working around it at runtime in a certain driver doesn't really
> matter, does it?

It needs to know what to patch and how so the result is still consistent.

How do you think the kernel is going to figure that out?

> They are both in-kernel ACPI fixes, just that one
> of the mechanisms is generic.

I'm not following you here, sorry.

> I don't understand why this obsession with userspace having
> to do the ACPI table patching - if kernels should "just work" then
> put this stuff behind Kconfig and have it in the kernel.

This is not an obsession and your suggestion here leads to having custom
per-board kernels which is not supportable in the long term.


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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