linux-kernel - Re: [PATCH RESEND 0/6 v10] gpio: Add block GPIO

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Date:	Mon, 17 Dec 2012 17:28:40 +0100
From:	Wolfgang Grandegger <wg@...ndegger.com>
To:	Roland Stigge <stigge@...com.de>
CC:	rmallon@...il.com, gregkh@...uxfoundation.org,
	linus.walleij@...aro.org, broonie@...nsource.wolfsonmicro.com,
	linux-kernel@...r.kernel.org, w.sang@...gutronix.de,
	grant.likely@...retlab.ca, daniel-gl@....net, sr@...x.de,
	plagnioj@...osoft.com, linux-arm-kernel@...ts.infradead.org,
	highguy@...il.com
Subject: Re: [PATCH RESEND 0/6 v10] gpio: Add block GPIO

On 12/17/2012 02:51 PM, Roland Stigge wrote:
> Hi Wolfgang,
> 
> On 12/17/2012 02:32 PM, Roland Stigge wrote:
>> And I guess Russell is right: If possible, we should write outputs
>> simultaneously via ODSR (plus OWER/OWDR/OWSR) instead of separate set/clear.
>>
>> I wonder if we need to save/restore the state of OWSR at every write
>> operation or if we need/can cache it. Assuming that block GPIO are the
>> only code in the kernel that manipulates ODSR.
> 
> Can you please test the following:
> 
> +static void at91_gpiolib_set_block(struct gpio_chip *chip, unsigned long mask, unsigned long val)
> +{
> +       struct at91_gpio_chip *at91_gpio = to_at91_gpio_chip(chip);
> +       void __iomem *pio = at91_gpio->regbase;
> +
> +       __raw_writel(~mask, pio + PIO_OWDR);

This would also disable normal GPIOs configured for output! From the
manual I understand that if the pin is configured for output, we could
either use PIO_SODR/PIO_CODR to set/clear the bits individually or
PIO_ODSR for synchronous data output. But than we need to care about the
non-block GPIO outputs as well... requiring a read-modify-write cycle :(.

Wolfgang.


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