Re: [PATCH 5/7] regmap: Check if a register is writable instead of readable in regcache_read

[Lars-Peter Clausen <lars@metafoo.de>]

On 11/16/2011 05:16 PM, Mark Brown wrote:
> 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...

Hm? The use case here is chips which do not support readback. So we never
want to fallback to a hardware read but still want to be able to do a cached
read.

> 
>> @@ -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.

Why? If a register is not writable we won't have anything in the cache for
it. So reading from the cache for a register which is not writable doesn't
make any sense.