Re: [RFC PATCH v2 19/19] hw/usb: Inline usb_bus_from_device()

[Thomas Huth]

On 13/02/2023 09.44, Philippe Mathieu-Daudé wrote:
> On 13/2/23 09:11, Thomas Huth wrote:
> > On 13/02/2023 08.08, Philippe Mathieu-Daudé wrote:
> > > Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
> > > ---
> > > RFC Other devices don't use such helper. Maybe it should
> > >      be the other way around, introduce more bus_from_device()
> > >      helpers?
> > > ---
> > >   hw/usb/bus.c        | 10 +++++-----
> > >   hw/usb/core.c       |  6 +++---
> > >   hw/usb/dev-hub.c    |  4 ++--
> > >   hw/usb/dev-serial.c | 10 +++++-----
> > >   hw/usb/hcd-xhci.c   |  2 +-
> > >   include/hw/usb.h    |  5 -----
> > >   6 files changed, 16 insertions(+), 21 deletions(-)
> > >
> > > diff --git a/hw/usb/bus.c b/hw/usb/bus.c
> > > index d7c3c71435..4a1b67761c 100644
> > > --- a/hw/usb/bus.c
> > > +++ b/hw/usb/bus.c
> > > @@ -427,7 +427,7 @@ void usb_unregister_port(USBBus *bus, USBPort *port)
> > >   void usb_claim_port(USBDevice *dev, Error **errp)
> > >   {
> > > -    USBBus *bus = usb_bus_from_device(dev);
> > > +    USBBus *bus = USB_BUS(qdev_get_parent_bus(DEVICE(dev)));
> >
> > You're certainly missing a proper justification in the patch description 
> > here. The "other devices don't use such a helper" does not sound like a 
> > real justification to me, since the code lines rather get longer this way. 
> > Thus this rather looks like unnecessary code churn to me --> rather drop 
> > the patch?
>
> The idea is to avoid having 7 different ways of implementing something
> with 3 different APIs and 2 unfinished API conversions in flight.

Ok, then please add such information to the patch description.

> I'm wondering if the QOM DECLARE_xxx() macros could also define some
> xxx_BUS_FROM_DEV() or xxx_PARENT_BUS() macros. So here it would become:
>
>      USBBus *bus = USB_PARENT_BUS(dev);

Sounds more readable at a first glance, but when looking at the output of:

  grep -r '(qdev_get_parent_bus' hw/

it seems like there aren't that many other places using this pattern (many 
places rather use BUS() instead), so it's maybe hard to justify such a 
change. Thus I think your patch here is likely the better solution right now 
(when you add a proper patch description).

 Thomas