linux-kernel - Re: [PATCH] ARM: at91: spi: request all csgpio in spi probe

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Date:	Thu, 31 Jul 2014 17:59:06 +0200
From:	Alexandre Belloni <alexandre.belloni@...e-electrons.com>
To:	Boris BREZILLON <boris.brezillon@...e-electrons.com>
Cc:	Jiří Prchal <jiri.prchal@...ignal.cz>,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, nicolas.ferre@...el.com,
	voice.shen@...el.com, Mark Brown <broonie@...nel.org>
Subject: Re: [PATCH] ARM: at91: spi: request all csgpio in spi probe

On 29/07/2014 at 10:00:17 +0200, Boris Brezillon wrote :
> Hi Alexandre,
> 
> > While this solves the particular issue Jiří is seeing, this will not
> > solve the case where PA14 (CS0) is not used by the spi driver at all. It
> > will remained muxed as CS0 and toggle when the spi master needs to
> > access CS0 until another driver muxes it to something else. I still
> > believe we should explicitly ask pinctrl to mux them as gpios.
> > 
> 
> Do we really care about this case ?
> After all, if a given pin needs a specific muxing during kernel boot
> (i.e. a pin connected to a gpio-led that needs to stay in its previous
> state or a pin connected to the reset line of a device that needs to
> stay up and running during kernel boot) the bootloader/bootstrap should
> have muxed this pin appropriately before booting the kernel.
> 

Yeah, you are right.


> What do you mean by "we should explicitly ask pinctrl to mux them as
> gpios" ?
> Do you mean configuring all the pins as GPIOs when the pin controller is
> probed, or just adding a new pinctrl state configuring the pin as an
> output GPIO and reference it in the pinctrl-0 property of the spi
> controller.
> 
> If the former, you'll break devices that needs their pins to stay in
> the state they were during the bootloader/boostrap phase.
> The latter won't work if the pin you request as GPIO is later requested
> by another device (which, if I'm correct, is exactly the case you're
> trying to solve).
> 

Again you are right, let's not care about that use case. I still feel
that the pinctrl-0 property has to be filled correctly.

-- 
Alexandre Belloni, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com
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