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

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Message-ID: <YupcPEbc0xD5pDtt@matsya>
Date:   Wed, 3 Aug 2022 17:00:04 +0530
From:   Vinod Koul <vkoul@...nel.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>,
        alsa-devel@...a-project.org, linux-kernel@...r.kernel.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 29-07-22, 17:03, Greg Kroah-Hartman wrote:
> On Fri, Jul 29, 2022 at 09:57:52AM -0500, Pierre-Louis Bossart wrote:
> > 
> > 
> > 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.
> 
> Is "dp0" a port?  If so, why isn't it a real device?

No they are not. It is a logical channel to send data to the device. The
device can have one or many data ports...

So the device logic or usb-endpoint style maynot look good here...

The change looks good though, dp0 maybe present and empty, we should
looks for attributes...

> > 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.
> 
> I don't understand what DSDT is, or how it is relevant here :(
> 
> thanks,
> 
> greg k-h

-- 
~Vinod