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

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Date:	Mon, 17 Dec 2012 14:51:58 +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

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);
+       __raw_writel(mask, pio + PIO_OWER);
+       __raw_writel(val, pio + PIO_ODSR);
+}

Would caching OWSR be a significant speedup here?

Thanks in advance,

Roland
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