linux-kernel - Re: Adding interrupt support to gpio-ich driver (possibly via SCI)

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Date:	Mon, 07 Apr 2014 21:02:29 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Matthew Garrett <mjg59@...f.ucam.org>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	Peter Tyser <ptyser@...-inc.com>,
	Mathias Nyman <mathias.nyman@...ux.intel.com>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>
Subject: Re: Adding interrupt support to gpio-ich driver (possibly via SCI)

On 04/07/2014 08:31 PM, Matthew Garrett wrote:
> On Mon, Apr 07, 2014 at 08:21:00PM -0700, Guenter Roeck wrote:
>> On 04/07/2014 07:48 PM, Matthew Garrett wrote:
>>> You shouldn't need to install an SCI handler - the way the hardware will
>>> generate an SCI is to raise a GPE. If you know which GPE the device
>>> raises (my recollection is that for most Intel chipsets it's GPIO number
>>> + 0x10) then you can just call acpi_install_gpe_handler(). The problem
>>
>> Sounds good. Do you by any chance have a pointer to some documentation
>> explaining this in some more detail ?
>
> The SCI is just IRQ 9 - it tells the OS that there's a firmware event,
> but in itself doesn't say what that event was. This is handled by the
> platform setting bits in the GPE*_STS registers. The ACPI code reads
> that and then dispatches the event to the appropriate handler. This will
> typically be some ACPI code (declared by _Lxx and _Exx methods in the
> ACPI tables - xx corresponds to the GPE number, L and E whether it's
> level or edge triggered), but in some cases you want to install a
> hardcoded event handler.
>
> I've only got the 5-series docs to hand, and I can't remember whether
> that's Panther Point, but you want to look at the definition of GPE0_STS
> to figure out which hardware events cause which GPEs. GPEs 16 to 31
> appear to correspond to GPIO 0 to 15, which is easy enough to handle.
>
Panther Point is Series 7 if I understand correctly, but the GPE0_STS
definition is the same.

That should get me started - thanks again!

Guenter

>>> is that the firmware may well already be using some of those GPIOs, and
>>> there's no easy way to tell. Checking the interrupt configuration isn't
>>> sufficient, since some of them may just be used as outputs.
>>>
>> The gpio-ich driver already has some magic to detect that condition - I
>> noticed that I can not request all GPIO pins on all hardware. Either case,
>> the gpio pins I am interested in are well defined on the hardware I am
>> dealing with, so I can be sure I won't step on some unexpected use.
>
> Ok. As long as you don't reprogram anything by default, I think this
> should be fine.
>

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