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SubjectRe: [PATCH v5 10/15] soundwire: Add sysfs for SoundWire DisCo properties
On Wed, Dec 13, 2017 at 03:24:30PM +0530, Vinod Koul wrote:
> On Wed, Dec 13, 2017 at 10:15:37AM +0100, Greg Kroah-Hartman wrote:
> > On Wed, Dec 06, 2017 at 09:17:06PM +0530, Vinod Koul wrote:
> > > It helps to read the properties for understanding and debugging
> > > systems, so add sysfs files for SoundWire DisCo properties.
> > >
> > > TODO: Add ABI files for sysfs
> >
> > Is this TODO done?
>
> Nope sorry not yet. But before this get merged will add
>
> > > + * Base file is:
> > > + * properties
> > > + * |---- interface-revision
> > > + * |---- master-count
> > > + * |---- link-N
> > > + * |---- clock-stop-modes
> > > + * |---- max-clock-frequency
> > > + * |---- clock-frequencies
> > > + * |---- default-frame-rows
> > > + * |---- default-frame-cols
> > > + * |---- dynamic-frame-shape
> > > + * |---- command-error-threshold
> > > + */
> >
> > Why nest them so deep? Anyway, that's not really an issue I guess, it's
> > your ABI, not mine :)
>
> well it gives us a hierarchical view. We have N links...

That's fine, then make it a real 'struct device' if you want to have a
reference counted object. Tie it to your bus, and you are good to go.
Don't use a raw kobject as that totaly breaks the device heirachy in the
kernel as well as preventing any of these attributes from being accessed
by userspace libraries (i.e. libudev.)

> > > +
> > > +struct sdw_master_sysfs {
> > > + struct kobject kobj;
> > > + struct sdw_bus *bus;
> >
> > Huh? Why do you need to use kobjects?
> >
> > When you switch from using a 'struct device' and hang a kobject off of
> > it, that's a huge signal that something is wrong here. That kobject
> > will now no longer be part of the device "chain" in the system, uevents
> > will get odd, and other strange things can happen.
> >
> > Why can't you just use "normal" attributes attached to the device? You
> > shouldn't need a kobject here. What am I missing?
>
> Okay my understanding might be incorrect then. So we can have N links in
> the system and each link would have a kobject for "link-N". Not sure how
> device attributes would do link-N/clock-stop-modes and so on, if they can
> let me know how and I will surely change that.

You can create a subdirectory for attributes quite easily. If you don't
want to make it a "full" object, and all you care about is the
subdirectory, then do it that way. Otherwise use a 'struct device'
please.

thanks,

greg k-h

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