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

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Message-ID: <CAErSpo4V-0Tnaf__fKUHM_69tBvfLySWzaoCWha9gimx0va1-w@mail.gmail.com>
Date:	Fri, 9 Nov 2012 09:35:46 -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 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 :)

> but there is first
> the non-trivial problem to solve of figuring out how ACPI/DT/whatever
> data maps into what the driver expects. For example, say a device uses
> two GPIOs (A & B) and we have a generic get_gpio(int index) function
> that works for both ACPI and DT. But what if the ACPI binding has the
> gpios in the order A,B and DT orders them B,A? I do want to coordinate
> between the DT and ACPI camps to avoid those situations as much as
> possible, but they will happen. When they do the driver will still
> need firmware specific data. It doesn't make any sense to put that
> stuff outside the driver because only that specific driver needs the
> extra information.

Sure.  This seems like just a special case of "drivers need a way to
access the underlying ACPI/DT/whatever-specific functionality," e.g.,

    gpio = get_gpio(dev, dev_is_acpi(dev) ? 1 : 0);
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