Re: [PATCH v1] usb: core: Add ACPI support for USB interfaces

[Andy Shevchenko <andriy.shevchenko@linux.intel.com>]

On Tue, Mar 24, 2020 at 07:26:35AM +0100, Greg Kroah-Hartman wrote:
> On Mon, Mar 23, 2020 at 09:55:43PM +0200, Andy Shevchenko wrote:
> > The ACPI companion of the device has to be set for USB interfaces
> > in order to read and attach the properties described in the ACPI table.
> > Use ACPI_COMPANION_SET macro to set this.
> > 
> > Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> > ---
> >  drivers/usb/core/message.c | 2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > diff --git a/drivers/usb/core/message.c b/drivers/usb/core/message.c
> > index 5adf489428aa..d5f834f16993 100644
> > --- a/drivers/usb/core/message.c
> > +++ b/drivers/usb/core/message.c
> > @@ -5,6 +5,7 @@
> >   * Released under the GPLv2 only.
> >   */
> >  
> > +#include <linux/acpi.h>
> >  #include <linux/pci.h>	/* for scatterlist macros */
> >  #include <linux/usb.h>
> >  #include <linux/module.h>
> > @@ -1941,6 +1942,7 @@ int usb_set_configuration(struct usb_device *dev, int configuration)
> >  			intf->dev.of_node = usb_of_get_interface_node(dev,
> >  					configuration, ifnum);
> >  		}
> > +		ACPI_COMPANION_SET(&intf->dev, ACPI_COMPANION(&dev->dev));
> >  		intf->dev.driver = NULL;
> >  		intf->dev.bus = &usb_bus_type;
> >  		intf->dev.type = &usb_if_device_type;
> 

> And what does this "fix"?

It links the firmware node of physical USB device to USB interface.
Otherwise it will be no firmware nodes under a corresponding folder.

It mimics what is done for OF in couple of lines above.

> Is this a new feature, what isn't working today without this change?

Yes, it is a new feature. I can't tell it fixes anything, because no complains
so far. I doubt it previously works.

> And if it is a fix, should it be backported to older kernels, how far?

No, no need for that. Usually I put Fixes tag when I would like change to be
considered for backporting.

I'll probably update the commit message to clarify all this. Would it be enough?

-- 
With Best Regards,
Andy Shevchenko