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From: shc_work@mail.ru (=?UTF-8?B?QWxleGFuZGVyIFNoaXlhbg==?=)
Date: Wed, 04 Dec 2013 14:16:06 +0400
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To: linux-arm-kernel@lists.infradead.org
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> > > > > > > On Sat, Nov 30, 2013 at 11:03:20AM +0400, Alexander Shiyan wrote:
> > > > > > > > This patch changes the default direction for pins used
> > > > > > > > as GPIO to "input". This prevents a short circuit on the
> > > > > > > > configuration stage when GPIO-pin is connected to the
> > > > > > > > other output pin.
> > > > > > > 
> > > > > > > Markus,
> > > > > > > 
> > > > > > > Does it make sense to you?
> > > > > > 
> > > > > > I am not sure if this really happens. However, it does make sense and I
> > > > > > can't see any disadvantages in changing the default GPIO mux direction to
> > > > > > input.
> > > > > > 
> > > > > What happens, if the bootloader already set up a pin as output and
> > > > > linux later does the pinconfig stuff?
> > > > > If the pin is reconfigured as input then, this may produce an unwanted
> > > > > glitch on the pin. IMO the pinconfig driver should not touch the pin
> > > > > direction, but leave it to the gpio driver to set that up. 
> > > > 
> > > > Such pin can be overridden by board DTS.
> > > > 
> > > So, which pins will be configured with the default direction?
> > > If pins are not stated in DT they should be not configured at all, I
> > > suppose.
> > 
> > Yes. We talk about GPIOs defined in DTS.
> > Just one example: We have one GPIO pin connected to switch between ground
> > and resistor to pullup (gpio-key driver). When pinctrl driver will initialize pin for the
> > driver (before gpio_direction_input() in the driver), direction will be set to output
> > and this may cause short circuit.
> > 
> The pin direction should be determined by the GPIO driver, not the

Direction determined by driver that use this GPIO pin,
setup this direction should be by GPIO driver.

> pinctrl driver. Pins that have been set up correctly by the bootloader
> must not change their direction when the pinctrl driver reconfigures
> the pins!

Yes. But this is another topic for discussion, it does not concern with this patch.

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