linux-kernel - Re: [PATCH 5/7] regmap: Check if a register is writable instead of readable in regcache

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Message-ID: <20111116161631.GK29986@opensource.wolfsonmicro.com>
Date:	Wed, 16 Nov 2011 16:16:31 +0000
From:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
To:	Lars-Peter Clausen <lars@...afoo.de>
Cc:	Dimitris Papastamos <dp@...nsource.wolfsonmicro.com>,
	Jonathan Cameron <jic23@...nel.org>,
	Michael Hennerich <michael.hennerich@...log.com>,
	linux-kernel@...r.kernel.org, linux-iio@...r.kernel.org,
	device-drivers-devel@...ckfin.uclinux.org, drivers@...log.com
Subject: Re: [PATCH 5/7] regmap: Check if a register is writable instead of
 readable in regcache_read

On Wed, Nov 16, 2011 at 04:28:20PM +0100, Lars-Peter Clausen wrote:

> Currently regcache checks whether a register is readable when performing a
> cached read and returns an error if not. Change this check to test whether the
> register is writable. This makes more sense, since reading from the cache when
> the register is not readable allows the operation described above, but if the
> register is not writable there shouldn't  be a value for it in the cache anyway.

This logic doesn't entirely follow - one can have registers which are
volatile but could be read once at startup.  Plus...

> @@ -206,7 +206,7 @@ int regcache_read(struct regmap *map,
>  
>  	BUG_ON(!map->cache_ops);
>  
> -	if (!regmap_readable(map, reg))
> +	if (!regmap_writeable(map, reg))
>  		return -EIO;

...the code winds up just looking like an obvious bug.
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