Message-ID: <600D5CB4DFD93545BF61FF01473D11AC0D87BDAD@limkexm2.ad.analog.com>
Date:	Fri, 17 Aug 2007 21:25:45 +0100
From:	"Hennerich, Michael" <Michael.Hennerich@...log.com>
To:	"David Brownell" <david-b@...bell.net>,
	"Mike Frysinger" <vapier.adi@...il.com>
Cc:	"Bryan Wu" <bryan.wu@...log.com>, <torvalds@...ux-foundation.org>,
	<linux-kernel@...r.kernel.org>, <akpm@...ux-foundation.org>,
	"Michael Hennerich" <michael.hennerich@...log.com>
Subject: RE: [PATCH 02/12] Blackfin arch: Add label to call new GPIO API



>-----Original Message-----
>From: David Brownell [mailto:david-b@...bell.net]
>
>On Friday 17 August 2007, Mike Frysinger wrote:
>> On 8/17/07, David Brownell <david-b@...bell.net> wrote:
>> > ...
>> > Just for the record, this is an unusual way to use these calls.
>> >
>> > Other platforms completely decouple these issues from the
>> > IRQ infrastructure ... doing the pinmux and gpio claiming
>> > separately from the request_irq()/free_irq() paths, mostly
>> > as part of board setup.  Doing all of that "early":
>> >
>> >  - keeps those error returns from causing hard-to-track-down
>> >    runtime bugs;
>> >
>> >  - works always, even on platforms where a given IRQ may
>> >    appear on any of several pins/balls;
>> >
>> >  - makes it easier to cross-check against board schematics,
>> >    by keeping most board-specific setup in one source file;
>> >
>> >  - shrinks the kernel's runtime footprint;
>> >
>> >  - allows the label to be more descriptive ... describeing
>> >    exactly *which* IRQ, so that using the labels for better
>> >    diagnostics actually gives better diagnostics.
>> >
>> > Again, not "wrong"; but probably sub-optimal.  You might
>> > want to move towards earlier binding now, while Linux is
>> > still young on Blackfin and you don't have legacy code to
>> > worry about.
>>
>> in the Blackfin port, if you want to use a pin as an IRQ rather than
>> GPIO, you use the normal request_irq/free_irq API ... those functions
>> will call back into the proper GPIO/PORTMUX code so that the pin is
>> setup properly.  this is done so that code isnt duplicated across
>> files and so that we can easily detect if someone does something
>> incorrect like try to take the same pin and use it as
>> irq/gpio/whatever at the same time ...
>>
>> are you saying that other ports dont unify the backend code paths at
all
>?
>
>Some platforms try to "unify" the pin setup in the boot loader.
>Most of them cope with bogus bootloaders by doing it in the board
>setup code.
>
>I don't know of any who try to do it "late" as you summarized.
>
>See above why "late" unification is not necessarily as good as
>"early" unification.
>
>And then there's the OMAP1 example, where for example you might
>know that you want MPUIO-0 but that's insufficient to tell whether
>you must mux ball F18 or R13 ... so it's impossible to do the kind
>of "late" unification done here, and pinmux *MUST* be separate from
>IRQ setup.

Dave,

We are not talking about PIN routing. One physical PIN/BALL can only
have one dedicated function the same time. It's more about telling about
possible conflicts, on a development board level.

What Mike wants to point out is that a external IRQ is first a GPIO and
needs to be configured like an INPUT GPIO and then a specific bit needs
to be set unmask it as IRQ.

So why not use the GPIO infrastructure to setup this pin as GPIO?

-Michael  

  


>
>- Dave
-
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