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

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Date:	Fri, 9 Nov 2012 09:53:26 -0700
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Grant Likely <grant.likely@...retlab.ca>
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 9:43 AM, Grant Likely <grant.likely@...retlab.ca> wrote:
> 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.

Yep, *that* makes perfect sense to me.  Something along these lines, maybe:

    #define dev_is_acpi(d)    ((d)->bus == &acpi_bus_type)
    #define dev_acpi_handle(d)    (dev_is_acpi(d) ? (acpi_handle)
d->datum : NULL)
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