linux-kernel - Re: [RFC PATCH 1/2] ASoC: soc-component: add snd_soc_component_read/write

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <6816a9fe-9b71-6a39-485e-1b6ce2b732ed@linaro.org>
Date:   Tue, 26 Jan 2021 14:03:29 +0000
From:   Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
To:     Mark Brown <broonie@...nel.org>
Cc:     lgirdwood@...il.com, alsa-devel@...a-project.org, perex@...ex.cz,
        tiwai@...e.com, linux-kernel@...r.kernel.org, vkoul@...nel.org
Subject: Re: [RFC PATCH 1/2] ASoC: soc-component: add
 snd_soc_component_read/write_field()



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
>