Re: [RFC PATCH 1/2] ASoC: soc-component: add snd_soc_component_read/write_field()

[Srinivas Kandagatla <srinivas.kandagatla@linaro.org>]

On 26/01/2021 13:36, Mark Brown wrote:
> On Tue, Jan 26, 2021 at 12:20:19PM +0000, Srinivas Kandagatla wrote:
> 
>> +#define __soc_component_field_shift(x) (__builtin_ffs(x) - 1)
> 
> Why not have this be a static inline?

Sure, that makes it even better to validate the mask aswell!

> 
>> +unsigned int snd_soc_component_read_field(struct snd_soc_component *component,
>> +					  unsigned int reg, unsigned int mask)
>> +{
>> +	unsigned int val;
>> +
>> +	mutex_lock(&component->io_mutex);
>> +	val = soc_component_read_no_lock(component, reg);
>> +	if (mask)
>> +		val = (val & mask) >> __soc_component_field_shift(mask);
> 
> I don't understand why this is open coding the locking when it's just a
> simple read and then shift?

I agree! something like this should be good I guess:

unsigned int snd_soc_component_read_field(...)
{
	unsigned int val;

	val = snd_soc_component_read(component, reg);

	val = (val & mask) >> __soc_component_field_shift(mask);

	return val;
}

> 
>> +	mutex_lock(&component->io_mutex);
>> +
>> +	old = soc_component_read_no_lock(component, reg);
>> +
>> +	val = val << __soc_component_field_shift(mask);
>> +
>> +	new = (old & ~mask) | (val & mask);
>> +
>> +	change = old != new;
>> +	if (change)
>> +		ret = soc_component_write_no_lock(component, reg, new);
>> +
>> +	mutex_unlock(&component->io_mutex);
> 
> This needs the lock as it's a read/modify/write but could also be
> implemented in terms of the existing update_bits() operation rather than
> open coding it.
True!, we could simplify this to :

int snd_soc_component_write_field(struct snd_soc_component *component,
				  unsigned int reg, unsigned int mask,
				  unsigned int val)
{
	val = (val << __soc_component_field_shift(mask)) & mask;

	return snd_soc_component_update_bits(component, reg, mask, val);
}

Does that look okay to you?


--srini
>