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SubjectRe: [PATCH 5/7] regmap: Check if a register is writable instead of readable in regcache_read
On 11/16/2011 05:38 PM, Mark Brown wrote:
> On Wed, Nov 16, 2011 at 05:34:33PM +0100, Lars-Peter Clausen wrote:
>> On 11/16/2011 05:16 PM, Mark Brown wrote:
>
>>> 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.
>
> This code will be run on every chip, including chips with read/write
> access. Caches are useful for all chips.

Of course. And it still works for chips with read/write support with this
patch, but it doesn't work for chips without read support without this patch.

>
>>>> @@ -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.
>
> If you're looking at the read function and it's checking to see if the
> register is writeable the first thought would be that this is a
> cut'n'paste error. The above code is at best *way* too cute.

We can of course add a comment explaining why it is regmap_writable instead
of regmap_readable.


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