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From: David Brownell <david-b@pacbell.net>
To: benh@kernel.crashing.org
Cc: avorontsov@ru.mvista.com, linux-kernel@vger.kernel.org,
	linuxppc-dev@ozlabs.org, i2c@lm-sensors.org,
	Jean Delvare <khali@linux-fr.org>,
	David Miller <davem@davemloft.net>
Subject: Re: [PATCH 4/7] gpiolib: implement dev_gpiochip_{add,remove} calls
Date: Wed, 22 Oct 2008 23:06:01 -0700	[thread overview]
Message-ID: <200810222306.01661.david-b@pacbell.net> (raw)
In-Reply-To: <1224737145.7654.387.camel@pasglop>

On Wednesday 22 October 2008, Benjamin Herrenschmidt wrote:
> On Wed, 2008-10-22 at 14:04 -0700, David Brownell wrote:
> > > So if we register the board infos after 
> > > the controller registered, then nobody will probe the board infos.
> > 
> > See above.  If you're doing it right, there's no problem.
> > That is, scan the OF tables early.  Just like PNP tables
> > get scanned early, for example.
> 
> It's still pretty yucky in that case to scan the device-tree to convert
> it into some kind of fugly board info ... I'd rather have the end
> drivers that actually use those GPIOs scan the device-tree directly.

Keep in mind that these problems are not specific to GPIOs.

And, very important!!, most of the drivers run without OF...

Pretty much any little device that needs board-specific
customization has the same class of problems:  drivers
will need a variety of parameters that may are often not
sharable with other devices, with idiosyncratic usage.
And they hook up to other drivers in arbitrary ways.

When PCs have such issues, ACPI hides them from Linux.

If those parameters -- potentially including callbacks
that escape to FORTH -- are stored in the OF device tree,
so be it.  But "fugly" sounds like part of that problem
domain, so it's no surprise that it maps onto the solution
space too...


Specifically with respect to GPIOs ... what do you mean
by "end driver" though?  I previously pointed at one
example (Davinci EVM) where one bank of GPIOs is used
by about six different drivers ... none of which have
any reason to know they're using a pcf8574a vs any other
kind of GPIO.  Is the "end driver" the IDE/CF driver?
The USB OTG driver?  The driver sitting the next layer
above of one of those?  *Some* of the drivers need to
touch the GPIOs.  Others don't.

 
> But then, I'm not a believer in generic drivers for things
> like GPIOs, i2c devices, etc.. :-)

I kind of like being able to re-use code myself.  ;)

It's a win to have *one* pcf8574/5 driver that can be
reused -- with a bit of care configuring it into the
system -- instead of having every board contribute yet
another board-specific hack in drivers/i2c/chips ...

And I think such stuff can be done even with OF.

- Dave

  reply	other threads:[~2008-10-23  6:06 UTC|newest]

Thread overview: 52+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-10-16 17:12 [PATCH 0/7 RFC] Handle I2C GPIO controllers with the OF (was: pca9539 I2C gpio expander) Anton Vorontsov
2008-10-16 17:12 ` [PATCH 1/7] powerpc and sparc: introduce dev_archdata node accessors Anton Vorontsov
2008-10-16 22:36   ` David Miller
2008-10-16 23:02     ` Grant Likely
2008-10-16 17:12 ` [PATCH 2/7] i2c: add info->archdata field Anton Vorontsov
2008-10-17  9:21   ` Jean Delvare
2008-10-22  0:27     ` Benjamin Herrenschmidt
2008-10-22  6:50       ` Jean Delvare
2008-10-22  7:37         ` Benjamin Herrenschmidt
2008-10-22 10:08           ` Anton Vorontsov
2008-10-22 11:07             ` Jean Delvare
2008-10-22 12:50               ` Anton Vorontsov
2008-10-16 17:12 ` [PATCH 3/7] of: fill the archdata for I2C devices Anton Vorontsov
2008-10-22  4:14   ` Grant Likely
2008-10-16 17:12 ` [PATCH 4/7] gpiolib: implement dev_gpiochip_{add,remove} calls Anton Vorontsov
2008-10-17 20:24   ` David Brownell
2008-10-17 21:29     ` Anton Vorontsov
2008-10-20  7:29       ` David Brownell
2008-10-20 15:48         ` Anton Vorontsov
2008-10-22  0:29           ` Benjamin Herrenschmidt
2008-10-22  1:03             ` Anton Vorontsov
2008-10-22  1:42               ` Anton Vorontsov
2008-10-22  2:28                 ` Benjamin Herrenschmidt
2008-10-22  4:20                   ` Grant Likely
2008-10-22  4:22                   ` David Brownell
2008-10-22 10:36                     ` Anton Vorontsov
2008-10-22 10:46                       ` Anton Vorontsov
2008-10-22 18:32                         ` Anton Vorontsov
2008-10-22 21:04                           ` David Brownell
2008-10-22 21:22                             ` Anton Vorontsov
2008-10-22 21:52                               ` David Brownell
2008-10-22 22:29                                 ` Anton Vorontsov
2008-10-23  5:19                                   ` David Brownell
2008-10-23  4:45                             ` Benjamin Herrenschmidt
2008-10-23  6:06                               ` David Brownell [this message]
2008-10-23  6:15                           ` David Brownell
2008-10-28 17:45                         ` [PATCH 0/6 RFC] OF-glue devices for I2C/SPI (was: " Anton Vorontsov
2008-10-28 17:46                           ` [PATCH 1/6] of/base: Add new helper of_should_create_pdev() Anton Vorontsov
2008-10-28 17:46                           ` [PATCH 2/6] of/of_i2c: implement of_{,un}register_i2c_device Anton Vorontsov
2008-10-28 17:46                           ` [PATCH 3/6] of/of_i2c: add support for dedicated OF I2C devices Anton Vorontsov
2008-10-28 18:41                             ` David Miller
2008-10-28 17:46                           ` [PATCH 4/6] of/gpio: add support for two-stage registration for the of_gpio_chips Anton Vorontsov
2008-10-28 17:46                           ` [PATCH 5/6] gpio/pca953x: pass gpio_chip pointer to the setup/teardown callbacks Anton Vorontsov
2008-10-28 17:46                           ` [PATCH 6/6] gpio: OpenFirmware bindings for the pca953x Anton Vorontsov
2008-10-28 17:53                           ` [PATCH 0/6 RFC] OF-glue devices for I2C/SPI (was: Re: [PATCH 4/7] gpiolib: implement dev_gpiochip_{add,remove} calls Grant Likely
2008-10-22  2:27               ` Benjamin Herrenschmidt
2008-10-16 17:13 ` [PATCH 5/7] of/gpio: implement of_dev_gpiochip_{add,remove} calls Anton Vorontsov
2008-10-17 20:25   ` David Brownell
2008-10-17 21:13     ` Anton Vorontsov
2008-10-16 17:13 ` [PATCH 6/7] gpio/pca953x: convert to dev_gpiochip_add and make it work with the OF Anton Vorontsov
2008-10-16 17:13 ` [PATCH 7/7] i2c/mcu_mpc8349emitx: convert to the new I2C/OF/GPIO infrastructure Anton Vorontsov
2008-10-17 16:07 ` [PATCH 0/7 RFC] Handle I2C GPIO controllers with the OF (was: pca9539 I2C gpio expander) Steven A. Falco

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