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Subject: Re: [RFC] regmap: allow volatile register writes with cached only
 read maps
To:     Mark Brown <broonie@kernel.org>
Cc:     linux-kernel@vger.kernel.org
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 <20180511020049.GD949@sirena.org.uk>
From:   Jorge Ramirez-Ortiz <jramirez@baylibre.com>
Message-ID: <7cc158bb-3471-4d8e-d066-2e7f535812eb@baylibre.com>
Date:   Fri, 11 May 2018 12:29:42 +0200
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On 05/11/2018 04:00 AM, Mark Brown wrote:
> On Wed, May 09, 2018 at 01:49:21PM +0200, Jorge Ramirez-Ortiz wrote:
>> On 05/09/2018 10:39 AM, Mark Brown wrote:
>>> I don't understand what voltile access means for write only devices.
>>> Volatile means that we don't read the cache but go direct to the
>>> hardware so if we can't read the hardware that's pretty redundant, a
>>> volatile read that goes to the cache is just a default read.
>> 1. only cached reads: (as a consequence every regmap write must succeed).
>> 2. cached writes: do not access the hardware unless the value differs from
>> what is in the cache already or (3) applies.
>> 3. support for selectable volatile writes: those that will always access the
>> device no matter what the cache holds.
> We don't currently suppress writes except when regmap_update_bits()
> notices that the modification was a noop.  You probably want to be using
> regmap_write_bits() here instead of regmap_update_bits(), that will
> always do the write.

but isnt that interface at a different level?
I am not sure if you are asking me to review my patch or just discarding 
the RFC and highlighting that I have a configuration problem.

In my use case and what triggered this RFC (config below), an 'amixer 
set' might never reach the driver's .reg_write interface even though the 
register is configured as volatile (to me this is not consistent since 
volatile_reg is being silently ignored).

So I dont see where/how your recommendation fits; maybe you could 
clarify a bit more please?

static const struct regmap_config foo_regmap = {
 ??? .reg_write??? ?????? = foo_write_reg,

 ??? .reg_bits??? ??????? = 32,
 ??? .val_bits??? ??????? = 32,
 ??? .reg_stride??? ????? = 1,

 ??? .volatile_reg??? ??? = foo_volatile_reg,

 ??? .max_register??? ??? = CODEC_ENABLE_DEBUG_CTRL_REG,
 ??? .reg_defaults??? ??? = foo_reg_defaults,
 ??? .num_reg_defaults??? = ARRAY_SIZE(foo_reg_defaults),
 ??? .cache_type??? ????? = REGCACHE_RBTREE,
};