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

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Date:	Mon, 17 Dec 2012 18:15:19 +0100
From:	Roland Stigge <stigge@...com.de>
To:	Wolfgang Grandegger <wg@...ndegger.com>
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 05:28 PM, Wolfgang Grandegger wrote:
> On 12/17/2012 02:51 PM, Roland Stigge wrote:
>> Hi Wolfgang,
>>> 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 :(.

>From the manual, I read about OWER: "Enables writing PIO_ODSR for the
I/O line" (analogous for OWDR). Would interpret this as affecting ODSR
(for block GPIO) but not SODR/CODR (as currently with single GPIOs).

Have you tried? ;-)

Thanks in advance,

Roland
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