Re: [alsa-devel] [RFC PATCH 2/7] soundwire: add Slave sysfs support

[Pierre-Louis Bossart]

On 5/6/19 11:22 AM, Vinod Koul wrote:
> On 06-05-19, 17:19, Greg KH wrote:
> > On Mon, May 06, 2019 at 09:42:35AM -0500, Pierre-Louis Bossart wrote:
> > > > > +
> > > > > +int sdw_sysfs_slave_init(struct sdw_slave *slave)
> > > > > +{
> > > > > +	struct sdw_slave_sysfs *sysfs;
> > > > > +	unsigned int src_dpns, sink_dpns, i, j;
> > > > > +	int err;
> > > > > +
> > > > > +	if (slave->sysfs) {
> > > > > +		dev_err(&slave->dev, "SDW Slave sysfs is already initialized\n");
> > > > > +		err = -EIO;
> > > > > +		goto err_ret;
> > > > > +	}
> > > > > +
> > > > > +	sysfs = kzalloc(sizeof(*sysfs), GFP_KERNEL);
> > > >
> > > > Same question as patch 1, why a new device?
> > >
> > > yes it's the same open. In this case, the slave devices are defined at a
> > > different level so it's also confusing to create a device to represent the
> > > slave properties. The code works but I am not sure the initial directions
> > > are correct.
> >
> > You can just make a subdir for your attributes by using the attribute
> > group name, if a subdirectory is needed just to keep things a bit more
> > organized.
>
> The key here is 'a subdir' which is not the case here. We did discuss
> this in the initial patches for SoundWire which had sysfs :)
>
> The way MIPI disco spec organized properties, we have dp0 and dpN
> properties each of them requires to have a subdir of their own and that
> was the reason why I coded it to be creating a device.

Vinod, the question was not for dp0 and dpN, it's fine to have 
subdirectories there, but rather why we need separate devices for the 
master and slave properties.

> Do we have a better way to handle this?
>
> > Otherwise, you need to mess with having multiple "types" of struct
> > device all associated with the same bus.  It is possible, and not that
> > hard, but I don't think you are doing that here.
> >
> > thnaks,
> >
> > greg k-h