linux-kernel - Re: [PATCH] drivers: create a pinmux subsystem v2

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Date:	Wed, 11 May 2011 00:58:53 +0100
From:	Jamie Iles <jamie@...ieiles.com>
To:	Linus Walleij <linus.walleij@...aro.org>
Cc:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	Martin Persson <martin.persson@...ricsson.com>,
	Lee Jones <lee.jones@...aro.org>,
	Stephen Warren <swarren@...dia.com>,
	Joe Perches <joe@...ches.com>,
	Russell King <linux@....linux.org.uk>
Subject: Re: [PATCH] drivers: create a pinmux subsystem v2

Hi Linus,

I haven't had chance to try this on my platform yet, but I have a couple 
of questions on how to deal with a few oddities that we have.

Thanks,

Jamie

On Wed, May 11, 2011 at 01:39:43AM +0200, Linus Walleij wrote:
> This creates a subsystem for handling of pinmux devices. These are
> devices that enable and disable groups of pins on primarily PGA and
> BGA type of chip packages and common in embedded systems.
> 
> This is being done to depopulate the arch/arm/* directory of such
> custom drivers and try to abstract the infrastructure they all
> need. See the Documentation/pinmux.txt file that is part of this
> patch for more details.
> 
> Cc: Stephen Warren <swarren@...dia.com>
> Cc: Joe Perches <joe@...ches.com>
> Cc: Russell King <linux@....linux.org.uk>
> Signed-off-by: Linus Walleij <linus.walleij@...aro.org>
> ---
[...]
> +static struct foo_pmx_func myfuncs[] = {
> +	{
> +		.name = "spi0-0",
> +		.pins = spi0_0_pins,
> +		.num_pins = ARRAY_SIZE(spi0_1_pins),
> +	},
> +	{
> +		.name = "i2c0",
> +		.pins = i2c0_pins,
> +		.num_pins = ARRAY_SIZE(i2c0_pins),
> +	},
> +	{
> +		.name = "spi0-1",
> +		.pins = spi0_1_pins,
> +		.num_pins = ARRAY_SIZE(spi0_1_pins),
> +	},
> +};

So I can see how this works well for these examples, but on our devices, 
we have some interfaces for connecting to radios and these have a pair 
of 8-bit RX and TX busses.  However, depending on what radio you 
connect, you may not need all 8 bits of each and this is dependent on 
the board.  What would be the best way to deal with that in this scheme 
where say we only wanted 4 bits of each, saving the others for GPIO?  
Would this need to be a function for each configuration?

[...]
> +/**
> + * pinmux_request_gpio() - request a single pin to be muxed in to be used
> + *	as a GPIO pin
> + * @pin: the pin to mux in as GPIO
> + * @gpio: the corresponding GPIO pin number
> + */
> +int pinmux_request_gpio(int pin, unsigned gpio)
> +{
> +	char gpiostr[16];
> +
> +	snprintf(gpiostr, 15, "gpio%d", gpio);
> +	return pin_request(pin, gpiostr, true);
> +}
> +EXPORT_SYMBOL_GPL(pinmux_request_gpio);

Our devices have two different GPIO controllers, which can be muxed to 
the same pad (they're slightly different - one is a bit slower but can 
do sigma-delta output) and our pinmux driver would need to know what 
GPIO controller it should route to the pad.  Could gpio_request_enable() 
be passed the GPIO number or is there a better way to do this?

Jamie
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