linux-kernel - Re: [PATCH 06/12] pinctrl/nomadik: implement pin configuration

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Message-ID: <4FAAD721.3070101@wwwdotorg.org>
Date:	Wed, 09 May 2012 14:44:17 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Linus Walleij <linus.walleij@...ricsson.com>
CC:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	Stephen Warren <swarren@...dia.com>,
	Shawn Guo <shawn.guo@...escale.com>,
	Thomas Abraham <thomas.abraham@...aro.org>,
	Dong Aisheng <dong.aisheng@...aro.org>,
	Rajendra Nayak <rajendra.nayak@...aro.org>,
	Haojian Zhuang <haojian.zhuang@...vell.com>,
	Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [PATCH 06/12] pinctrl/nomadik: implement pin configuration

On 05/08/2012 03:45 AM, Linus Walleij wrote:
> From: Linus Walleij <linus.walleij@...aro.org>
> 
> This implements the pin configuration interface for the
> Nomadik pin controller.
> 
> As part of the exercise we add a bit in the pin_cfg_t for
> the Nomadik pinctrl driver that indicates if the pin should
> be forced into GPIO mode. This is not done to go behind the
> back of the GPIO subsystem, but to ensure that default modes
> can be set by hogs on boot and system suspend/resume states.
> It was used implicitly by the old code defining all config
> settings and modes in a single config word but we now have
> a split between pinmux and pinconf leading to the need to
> have this.

Yes, I have wondered if we should have always represented the
GPIO/pinctrl interaction as a pinctrl "function" of "GPIO. There are a
few gotchas that prevented me moving forward with this though:

1) On Tegra at least, GPIO-vs-pinmux is actually a bit in the GPIO
controller, so that mux is after the pinmux's output mux

2) I'm not sure how it'd work when you could mux "GPIO controller A GPIO
x" or "GPIO controller B pin y" onto the same pinctrl pin

3) On Tegra at least, special-function muxing is at a per-pingroup
level, but GPIO muxing is at a per-pin level. So much for regular HW:-(

> @@ -1561,7 +1562,8 @@ int nmk_gpio_request_enable(struct pinctrl_dev *pctldev,
>  
>  	clk_enable(nmk_chip->clk);
>  	bit = offset % NMK_GPIO_PER_CHIP;
> -	__nmk_gpio_set_mode_safe(nmk_chip, bit, NMK_GPIO_ALT_GPIO, false);
> +	/* There is no glitch when converting any pin to GPIO */
> +	__nmk_gpio_set_mode(nmk_chip, bit, NMK_GPIO_ALT_GPIO);

Was that meant to be squashed into some other earlier change?
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