From: Nate Case <ncase@xes-inc•com>
To: Peter Korsgaard <jacmet@sunsite•dk>
Cc: linuxppc-dev@ozlabs•org, Trent Piepho <tpiepho@freescale•com>
Subject: Re: [v5] powerpc: gpio driver for mpc8349/8572/8610 and compatible
Date: Thu, 30 Oct 2008 09:39:35 -0500 [thread overview]
Message-ID: <1225377575.27415.99.camel@localhost.localdomain> (raw)
In-Reply-To: <8763najzl1.fsf@macbook.be.48ers.dk>
On Thu, 2008-10-30 at 08:45 +0100, Peter Korsgaard wrote:
> I would write a dedicated driver for something like that instead of
> using gpiolib.
>
> Gpiolib has quite some overhead compared to the actual work for
> changing a SoC gpio pin, but it also has some very nice
> advantages. For most stuff people use GPIO pins for, the overhead is
> not an issue (SPI chip selects, leds, keys, reset signals, ..). It's
> very handy that we nowadays have generic drivers that work with any
> GPIO (being SoC gpios or stuff on spi/i2c).
For what it's worth, I think it could be useful to have an optimally
fast gpiolib driver. This would let you have truly generic bit-bang
drivers. Take a look at drivers/spi for example -- there's ~7 bit-bang
drivers in there that use spi_bitbang.c for a library of functions. I
am not familiar with these drivers, but at a glance it seems feasible
that with fast gpiolib implementations you could reduce all of those to
a single spi_bitbang.c driver.
Trent, it looks like the big performance wins for you were obtained by
deviating from the gpiolib interface? In that case a generic SPI/JTAG
bit bang driver wouldn't benefit from the speed boosts in your MPC8572
GPIO driver (without explicitly calling mpc8572_gpio_lock and
_mpc8572_gpio_set, etc). Is that correct? In any case, I appreciate
what you did with your driver, so please don't give up on getting some
of your bits merged in :)
--
Nate Case <ncase@xes-inc•com>
next prev parent reply other threads:[~2008-10-30 14:40 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-09-23 15:35 [PATCH v5] powerpc: gpio driver for mpc8349/8572/8610 and compatible Peter Korsgaard
2008-09-23 15:42 ` Kumar Gala
2008-10-30 1:07 ` [v5] " Trent Piepho
2008-10-30 7:45 ` Peter Korsgaard
2008-10-30 8:58 ` Trent Piepho
2008-10-30 13:44 ` Kumar Gala
2008-10-30 14:39 ` Nate Case [this message]
2008-10-30 18:04 ` Anton Vorontsov
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