linux-kernel - Re: [PATCH v3 3/3] gpio: add Intel SCH GPIO controller driver

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Message-ID: <4B84CC0E.5060203@compulab.co.il>
Date:	Wed, 24 Feb 2010 08:49:50 +0200
From:	Mike Rapoport <mike@...pulab.co.il>
To:	David Brownell <david-b@...bell.net>
CC:	Denis Turischev <denis@...pulab.co.il>,
	Samuel Ortiz <sameo@...ux.intel.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Mike Rapoport <mike@...pulab.co.il>
Subject: Re: [PATCH v3 3/3] gpio: add Intel SCH GPIO controller driver

David Brownell wrote:
> On Sunday 21 February 2010, Denis Turischev wrote:
>> v2: there is no acpi_check_region, it will be implemented in mfd-core
>> v3: patch refreshed against the latest Linus tree
> 
> Could such call really address the GPIO conflict issue I mentioned?
> 
> The AML bytecodes I looked at were writing directly to Southbridge
> GPIO registers (or reading them), or relying on ACPI to mediate the
> GPIO interrupts.  ISTR that button drivers, and code to switch into
> or out of low power states, were good sources of such bad examples.

I'm really not an ACPI expert, but as far as I understand possibility of 
such conflicts largely depends on particular board/BIOS implementation. 
On the hardware we have such conflict cannot happen, unless there are 
bugs in ACPI we are not yet aware of. :)

> Calls like that should clearly be able to handle cases where ACPI
> has a "Real" Driver (tm) ... e.g. for SMBus hardware.
> 
> I'm not sure what a good solution for this would be, short of just
> not using ACPI ... which may not be practical, given the limited
> degree of x86 board/system support for Linux.
> 
> I mention this mostly because when I looked at the issue in the
> context of an ICHx GPIO driver, I didn't see a good solution to
> the problem then ... and nothing seems to have changed meanwhile.

I've looked at two x86 drivers in drivers/gpiolib (cs5535 and langwell) 
and there's no treatment of ACPI in either of them. Since SCH is defined 
by Intel as "embedded" product, having a GPIO driver for it seems 
logical even despite problems you mention.

> - Dave
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-- 
Sincerely yours,
Mike.

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