linux-kernel - Re: [RFC] gpio/stmpe: add bitmask to block requests to unavailable GPIOs

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Date:	Wed, 18 Aug 2010 12:31:37 +0200
From:	Wolfram Sang <w.sang@...gutronix.de>
To:	Rabin VINCENT <rabin.vincent@...ricsson.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linus WALLEIJ <linus.walleij@...ricsson.com>,
	Samuel Ortiz <sameo@...ux.intel.com>
Subject: Re: [RFC] gpio/stmpe: add bitmask to block requests to unavailable
 GPIOs

On Wed, Aug 18, 2010 at 03:39:50PM +0530, Rabin VINCENT wrote:
> On Mon, Aug 16, 2010 at 17:14:44 +0200, Wolfram Sang wrote:
> > GPIOs on these controller are multi-functional. If you decided to use
> > some of them e.g. as input channels for the ADC, you surely don't want
> > those pins to be reassigned as simple GPIOs (which may be triggered even
> > from userspace via 'export'). Same for the touchscreen controller pins.
> > Since knowledge about the hardware is needed to decide which GPIOs to
> > reserve, let this bitmask be inside platform_data and provide some
> > defines to assist potential users.
> 
> Could this be done without the platform data, say something like the
> below?  (Though this does assume that nobody tries to request GPIOs
> before the STMPE subdrivers reserve their pins.)
> 

While I'd also like to skip the additional platform_data entry, your
last comment is in deed a drawback. Also, when thinking of a generic
solution (ADC comes to my mind), you can't make an assumption which pins
will have the alternate function as you can do with the touchscreen
driver. If a pin is an ADC-input channel or a GPIO, that is board
design.

Regards,

   Wolfram

> diff --git a/drivers/input/touchscreen/stmpe-ts.c b/drivers/input/touchscreen/stmpe-ts.c
> index 656148e..d1595f9 100644
> --- a/drivers/input/touchscreen/stmpe-ts.c
> +++ b/drivers/input/touchscreen/stmpe-ts.c
> @@ -179,6 +179,12 @@ static int __devinit stmpe_init_hw(struct stmpe_touch *ts)
>  		return ret;
>  	}
>  
> +	ret = stmpe_set_altfunc(stmpe, 0xf0, STMPE_BLOCK_TOUCHSCREEN);
> +	if (ret) {
> +		dev_err(dev, "Could not enable alternate function for pins\n");
> +		return ret;
> +	}
> +
>  	adc_ctrl1 = SAMPLE_TIME(ts->sample_time) | MOD_12B(ts->mod_12b) |
>  		REF_SEL(ts->ref_sel);
>  	adc_ctrl1_mask = SAMPLE_TIME(0xff) | MOD_12B(0xff) | REF_SEL(0xff);
> diff --git a/drivers/mfd/stmpe.c b/drivers/mfd/stmpe.c
> index 0754c5e9..4f748fa 100644
> --- a/drivers/mfd/stmpe.c
> +++ b/drivers/mfd/stmpe.c
> @@ -253,6 +253,12 @@ int stmpe_set_altfunc(struct stmpe *stmpe, u32 pins, enum stmpe_block block)
>  
>  	mutex_lock(&stmpe->lock);
>  
> +	if (block == STMPE_BLOCK_GPIO && (pins & stmpe->af_pins)) {
> +		dev_dbg(stmpe->dev, "not allowing change of AF pins to GPIO\n");
> +		ret = -EBUSY;
> +		goto out;
> +	}
> +
>  	ret = __stmpe_enable(stmpe, STMPE_BLOCK_GPIO);
>  	if (ret < 0)
>  		goto out;
> @@ -274,6 +280,11 @@ int stmpe_set_altfunc(struct stmpe *stmpe, u32 pins, enum stmpe_block block)
>  		pins &= ~(1 << pin);
>  	}
>  
> +	if (block == STMPE_BLOCK_GPIO)
> +		stmpe->af_pins &= ~pins;
> +	else
> +		stmpe->af_pins |= pins;
> +
>  	ret = __stmpe_block_write(stmpe, regaddr, numregs, regs);
>  
>  out:
> diff --git a/include/linux/mfd/stmpe.h b/include/linux/mfd/stmpe.h
> index 39ca758..ba5a847 100644
> --- a/include/linux/mfd/stmpe.h
> +++ b/include/linux/mfd/stmpe.h
> @@ -64,6 +64,7 @@ struct stmpe_variant_info;
>   * @num_gpios: number of gpios, differs for variants
>   * @ier: cache of IER registers for bus_lock
>   * @oldier: cache of IER registers for bus_lock
> + * @af_pins: mask of pins set in alternate function mode
>   * @pdata: platform data
>   */
>  struct stmpe {
> @@ -79,6 +80,7 @@ struct stmpe {
>  	int num_gpios;
>  	u8 ier[2];
>  	u8 oldier[2];
> +	u32 af_pins;
>  	struct stmpe_platform_data *pdata;
>  };
>  

-- 
Pengutronix e.K.                           | Wolfram Sang                |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |

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