linux-kernel - Re: [PATCH 2/3] spi / ACPI: add ACPI enumeration support

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Message-ID: <CACxGe6vgYKv92x8qk5dbdA8UJNJPVxT_1p5Mn58NfBfVF3x+iQ@mail.gmail.com>
Date:	Fri, 9 Nov 2012 16:43:27 +0000
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
Cc:	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>, linux-kernel@...r.kernel.org,
	lenb@...nel.org, rafael.j.wysocki@...el.com,
	broonie@...nsource.wolfsonmicro.com, linus.walleij@...aro.org,
	khali@...ux-fr.org, ben-linux@...ff.org, w.sang@...gutronix.de,
	mathias.nyman@...ux.intel.com, linux-acpi@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"H. Peter Anvin" <hpa@...or.com>, Tony Luck <tony.luck@...el.com>
Subject: Re: [PATCH 2/3] spi / ACPI: add ACPI enumeration support

On Fri, Nov 9, 2012 at 4:35 PM, Bjorn Helgaas <bhelgaas@...gle.com> wrote:
> On Fri, Nov 9, 2012 at 8:45 AM, Grant Likely <grant.likely@...retlab.ca> wrote:
>> On Fri, Nov 9, 2012 at 3:11 PM, Bjorn Helgaas <bhelgaas@...gle.com> wrote:
>>> [+cc Greg, Peter, Tony since they acked the original patch [1]]
>>>
>>> On Thu, Nov 8, 2012 at 1:04 PM, Mika Westerberg
>>> <mika.westerberg@...ux.intel.com> wrote:
>>>> On Thu, Nov 08, 2012 at 12:32:25PM -0700, Bjorn Helgaas wrote:
>>>>> Struct device_driver is a generic structure, so it seems strange to
>>>>> have to include non-generic things like of_device_id and now
>>>>> acpi_match_table there.
>>>>
>>>> Yes, but in a sense the DT and ACPI are "generic". So that they are used to
>>>> describe the configuration of a machine.
>>>
>>> What I meant by "generic" was "useful across all architectures."  The
>>> new acpi_match_table and acpi_handle fields [1] are not generic in
>>> that sense because they're present on all architectures but used only
>>> on x86 and ia64.  The existing of_match_table and of_node are
>>> similarly unused on many architectures.  This doesn't seem like a
>>> scalable strategy to me.  Are we going to add a pnpbios_node for x86
>>> PNPBIOS machines without ACPI, a pdc_hpa for parisc machines with PDC,
>>> etc.?
>>>
>>> [1] https://patchwork.kernel.org/patch/1677221/
>>
>> Ultimately yes, I think that is what we want to do,
>
> Just to be clear, you think we *should* add things like pnpbios_node,
> pdc_hpa, etc., to struct device, one field for every scheme of telling
> the OS about non-enumerable devices, where only one of the N fields is
> used on any given machine?  That seems surprising to me, but maybe I
> just need to be educated :)

Ah, I see what you're asking.

In the short term, yes but only because we don't have any other
alternative. What I'd really rather have is a safe way to attach datum
(ie. acpi_device or device_node) to a struct device and get it back
later in a type safe way. It would actually be useful for all manner
of things, not just ACPI/DT. I experimented a bit with trying to
implement something a year back, but never spent enough time on it.

g.
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