linux-kernel - Re: [PATCH 2/5] soundwire: sysfs: cleanup the logic for creating the dp0 sysfs attributes

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Date:   Fri, 29 Jul 2022 09:57:52 -0500
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
        Vinod Koul <vkoul@...nel.org>,
        Sanyog Kale <sanyog.r.kale@...el.com>,
        Bard Liao <yung-chuan.liao@...ux.intel.com>
Subject: Re: [PATCH 2/5] soundwire: sysfs: cleanup the logic for creating the
 dp0 sysfs attributes



On 7/29/22 09:52, Greg Kroah-Hartman wrote:
> On Fri, Jul 29, 2022 at 09:46:26AM -0500, Pierre-Louis Bossart wrote:
>>
>>
>> On 7/29/22 08:50, Greg Kroah-Hartman wrote:
>>> There's no need to special-case the dp0 sysfs attributes, the
>>> is_visible() callback in the attribute group can handle that for us, so
>>> add that and add it to the attribute group list making the logic simpler
>>> overall.
>>>
>>> This is a step on the way to moving all of the sysfs attribute handling
>>> into the default driver core attribute group logic so that the soundwire
>>> core does not have to do any of it manually.
>>>
>>> Cc: Vinod Koul <vkoul@...nel.org>
>>> Cc: Bard Liao <yung-chuan.liao@...ux.intel.com>
>>> Cc: Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
>>> Cc: Sanyog Kale <sanyog.r.kale@...el.com>
>>> Cc: alsa-devel@...a-project.org
>>> Cc: linux-kernel@...r.kernel.org
>>> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>>> ---
>>>  drivers/soundwire/sysfs_slave.c | 18 ++++++++++++------
>>>  1 file changed, 12 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/drivers/soundwire/sysfs_slave.c b/drivers/soundwire/sysfs_slave.c
>>> index 83e3f6cc3250..3723333a5c2b 100644
>>> --- a/drivers/soundwire/sysfs_slave.c
>>> +++ b/drivers/soundwire/sysfs_slave.c
>>> @@ -174,6 +174,16 @@ static ssize_t words_show(struct device *dev,
>>>  }
>>>  static DEVICE_ATTR_RO(words);
>>>  
>>> +static umode_t dp0_is_visible(struct kobject *kobj, struct attribute *attr,
>>> +			      int n)
>>> +{
>>> +	struct sdw_slave *slave = dev_to_sdw_dev(kobj_to_dev(kobj));
>>> +
>>> +	if (slave->prop.dp0_prop)
>>> +		return attr->mode;
>>> +	return 0;
>>> +}
>>
>> This changes the results slightly by creating an empty 'dp0' directory
>> with no attributes inside.
>>
>> Before:
>>
>> [root@...ora ~]# cd /sys/bus/soundwire/devices/sdw:3:025d:0714:01
>> [root@...ora sdw:3:025d:0714:01]# ls dp0
>> ls: cannot access 'dp0': No such file or directory
>>
>> After:
>> [root@...ora sdw:3:025d:0714:01]# ls dp0
> 
> That should be fine, tools should just be looking for the attributes,
> not the existance of a directory, right?

The idea what that we would only expose ports that actually exist.
That's helpful information anyone with a basic knowledge of the
SoundWire specification would understand.

The attributes are really details that few people/applications would
understand, and unfortunately the information reported in DSDT is more
often than not complete garbage.