linux-kernel - Re: [PATCH 1/2] gpio/gpio-generic: read set register for caching if available

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Message-ID: <20110704154447.GG29977@ponder.secretlab.ca>
Date:	Mon, 4 Jul 2011 09:44:47 -0600
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:	linux-kernel@...r.kernel.org, sodaville@...utronix.de
Subject: Re: [PATCH 1/2] gpio/gpio-generic: read set register for caching if
 available

On Mon, Jun 27, 2011 at 09:26:22AM +0200, Sebastian Andrzej Siewior wrote:
> The ->data is a shadow copy which is used during the ->set callback in
> order to avoid a read of the register before write.
> If ->reg_set is set then we write to this location therefore we should
> cache that value.
> 
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> ---
>  drivers/gpio/gpio-generic.c |    5 ++++-
>  1 files changed, 4 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/gpio/gpio-generic.c b/drivers/gpio/gpio-generic.c
> index 231714d..9f8b5c6 100644
> --- a/drivers/gpio/gpio-generic.c
> +++ b/drivers/gpio/gpio-generic.c
> @@ -398,7 +398,10 @@ int __devinit bgpio_init(struct bgpio_chip *bgc,
>  	if (ret)
>  		return ret;
>  
> -	bgc->data = bgc->read_reg(bgc->reg_dat);
> +	if (bgc->reg_set)
> +		bgc->data = bgc->read_reg(bgc->reg_set);

On most of the gpio controllers that I've seen, the 'set' register
isn't something that you can actually read.  I don't think this is
something that can be done for all gpio controllers.

g.

> +	else
> +		bgc->data = bgc->read_reg(bgc->reg_dat);
>  
>  	return ret;
>  }
> -- 
> 1.7.4.4
> 
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