linux-kernel - Re: [PATCH 001/001] gpio-mxs: Select faster gpio-generic set methods

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Date:	Mon, 24 Jun 2013 14:59:30 +0800
From:	Shawn Guo <shawn.guo@...aro.org>
To:	Simon Pearson <spearson@...malabs.com>
CC:	<grant.likely@...retlab.ca>, <linus.walleij@...aro.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 001/001] gpio-mxs: Select faster gpio-generic set methods

On Fri, Jun 21, 2013 at 11:14:07AM -0700, Simon Pearson wrote:
> From: Simon Pearson <spearson@...malabs.com>
> 
> Kernel 3.8.4.  By defining both the set and clear registers,
> the speed of the gpio isimproved. gpio-generic.c, selects the
> bgpio_set_with_clear() which isfaster than the current
> bgpio_set_set().  This has performance implications for all
> bitbang drivers (i2c, spi, etc).  Slow SPI as compared to
> 2.6.35.33 improved by a factor of 10 (80kHz CLK to 800kHz CLK).
> 
> Signed-off-by: Simon Pearson <spearson@...malabs.com>

The latest mainline kernel already has the improvement made by commit
90dae4e (gpio: mxs: Use set and clear capabilities of the gpio
controller).

Shawn

> 
> ---
> --- a/drivers/gpio/gpio-mxs.c.orig    2013-03-20 13:11:19.000000000 -0700
> +++ b/drivers/gpio/gpio-mxs.c    2013-06-21 10:02:33.000000000 -0700
> @@ -292,7 +292,8 @@ static int mxs_gpio_probe(struct platfor
> 
>      err = bgpio_init(&port->bgc, &pdev->dev, 4,
>               port->base + PINCTRL_DIN(port),
> -             port->base + PINCTRL_DOUT(port), NULL,
> +             port->base + PINCTRL_DOUT(port) + MXS_SET,
> +             port->base + PINCTRL_DOUT(port) + MXS_CLR,
>               port->base + PINCTRL_DOE(port), NULL, 0);
>      if (err)
>          goto out_irqdesc_free;

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