[alsa-devel] [PATCH] ASoC: rsnd: Protect register accesses with a spinlock instead of a mutex

[Lars-Peter Clausen]

On 07/24/2014 04:16 AM, Kuninori Morimoto wrote:
>
> Hi Laurent
>
>>> The hardware registers are accessed from atomic contexts (the
>>> rsnd_soc_dai_trigger function, for instance, is called with the PCM
>>> substream spinlock held). They thus can't be protected by a mutex.
>>>
>>> Protect regmap register accesses with a spinlock instead of a mutex by
>>> setting the fast_io flag.
>>>
>>> Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas at ideasonboard.com>
>>> ---
>>>   sound/soc/sh/rcar/gen.c | 1 +
>>>   1 file changed, 1 insertion(+)
>>>
>>> An even better solution might be to use regmap-mmio instead of a custom bus.
>>> Morimoto-san, is there anything that would prevent the driver from switching
>>> to regmap-mmio ?
>>
>> I guess it is possilbe to use regmap-mmio.
>> I check it.
>
> Hmm... rsnd driver is using "regmap_field".
> regmap-mmio  requests "offset"  on "reg"
> regmap-filed requests "address" on "reg"
>
> So, if rsnd driver uses regmap-mmio,
> then, it needs tricky initialize like...
>
>        regmap_init_mmio(dev, 0, config)
>

Create one regmap instance per base address and in the regmap_fields use an 
relative offset to the base address rather than the absolute address. That's 
how the API is intended to be used, the current implementation is quite a hack.

- Lars