linux-kernel - Re: [PATCH] gpio: pca953x: Don't flip bits on PCA957x GPIO expanders when probing them.

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Date:	Sun, 4 Aug 2013 20:35:51 +0800
From:	Haojian Zhuang <haojian.zhuang@...il.com>
To:	Graeme Smecher <gsmecher@...eespeedlogic.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Grant Likely <grant.likely@...aro.org>,
	Haojian Zhuang <haojian.zhuang@...vell.com>
Subject: Re: [PATCH] gpio: pca953x: Don't flip bits on PCA957x GPIO expanders
 when probing them.

On Sat, Aug 3, 2013 at 5:24 AM, Graeme Smecher
<gsmecher@...eespeedlogic.com> wrote:
> The pca957x driver supports a handful of I2C GPIO expanders from NXP, Maxim,
> and TI. For the PCA9574 and PCA9575 devices only, the driver resets the GPIO
> level and direction in the pca957x_probe function. This seems like the wrong
> thing to do, since it can cause hardware bit twiddles during warm reboots when
> the chip state and reset values don't match.
>
> This kind of initialization is best left upstream (in a bootloader) or
> downstream (in userspace). It's also an inconsistency across devices supported
> by this driver.
>
> Signed-off-by: Graeme Smecher <gsmecher@...eespeedlogic.com>
> Cc: Grant Likely <grant.likely@...aro.org>
> Cc: Haojian Zhuang <haojian.zhuang@...vell.com>
> ---
>  drivers/gpio/gpio-pca953x.c |   11 -----------
>  1 file changed, 11 deletions(-)
>
> diff --git a/drivers/gpio/gpio-pca953x.c b/drivers/gpio/gpio-pca953x.c
> index 426c51d..47c08d8 100644
> --- a/drivers/gpio/gpio-pca953x.c
> +++ b/drivers/gpio/gpio-pca953x.c
> @@ -683,17 +683,6 @@ static int device_pca957x_init(struct pca953x_chip *chip, u32 invert)
>         int ret;
>         u8 val[MAX_BANK];
>
> -       /* Let every port in proper state, that could save power */
> -       memset(val, 0, NBANK(chip));
> -       pca953x_write_regs(chip, PCA957X_PUPD, val);
> -       memset(val, 0xFF, NBANK(chip));
> -       pca953x_write_regs(chip, PCA957X_CFG, val);
> -       memset(val, 0, NBANK(chip));
> -       pca953x_write_regs(chip, PCA957X_OUT, val);
> -
> -       ret = pca953x_read_regs(chip, PCA957X_IN, val);
> -       if (ret)
> -               goto out;
>         ret = pca953x_read_regs(chip, PCA957X_OUT, chip->reg_output);
>         if (ret)
>                 goto out;
> --
> 1.7.10.4
>

Acked-by: Haojian Zhuang <haojian.zhuang@...il.com>
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