linux-kernel - Re: [PATCH v2 1/6] software node: Provide replacement for device_add

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Date:   Thu, 4 Feb 2021 17:13:04 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Felipe Balbi <balbi@...nel.org>,
        Mathias Nyman <mathias.nyman@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:ULTRA-WIDEBAND (UWB) SUBSYSTEM:" 
        <linux-usb@...r.kernel.org>
Subject: Re: [PATCH v2 1/6] software node: Provide replacement for
 device_add_properties()

On Thu, Feb 04, 2021 at 05:06:53PM +0100, Rafael J. Wysocki wrote:
> On Thu, Feb 4, 2021 at 3:17 PM Heikki Krogerus
> <heikki.krogerus@...ux.intel.com> wrote:
> >
> > At the moment the function device_del() is calling
> > device_remove_properties() unconditionally. That will result into the
> > reference count of the software node attached to the device being
> > decremented, and in most cases it will hit 0 at that point. So in
> > practice device_del() will unregister the software node attached to
> > the device, even if that was not the intention of the caller. Right
> > now software nodes can not be reused or shared because of that.
> >
> > So device_del() can not unregister the software nodes unconditionally
> > like that. Unfortunately some of the users of device_add_properties()
> > are now relying on this behaviour. Because of that, and also in
> > general, we do need a function that can offer similar behaviour where
> > the lifetime of the software node is bound to the lifetime of the
> > device. But it just has to be a separate function so the behaviour is
> > optional. We can not remove the device_remove_properties() call from
> > device_del() before we have that new function, and before we have
> > replaced device_add_properties() calls with it in all the places that
> > require that behaviour.
> >
> > This adds function device_create_managed_software_node() that can be
> > used for exactly that purpose. Software nodes created with it are
> > declared "managed", and separate handling for those nodes is added to
> > the software node code. The reference count of the "managed" nodes is
> > decremented when the device they are attached to is removed. This will
> > not affect the other nodes that are not declared "managed".
> >
> > The function device_create_managed_software_node() has also one
> > additional feature that device_add_properties() does not have. It
> > allows the software nodes created with it to be part of a node
> > hierarchy by taking also an optional parent node as parameter.
> >
> > Signed-off-by: Heikki Krogerus <heikki.krogerus@...ux.intel.com>
> 
> The rationale is clear now, so
> 
> Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> and I'm assuming that this will be routed via the USB tree.

Yes, I will do so, thanks.

greg k-h