linux-kernel - Re: [PATCH v2 04/16] thunderbolt: ACPI: Replace tb_acpi_find_port() with acpi_find_child_by

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Date:   Wed, 15 Jun 2022 09:27:46 +0300
From:   Mika Westerberg <mika.westerberg@...ux.intel.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux ACPI <linux-acpi@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Hans de Goede <hdegoede@...hat.com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Andreas Noever <andreas.noever@...il.com>,
        Michael Jamet <michael.jamet@...el.com>,
        Yehezkel Bernat <YehezkelShB@...il.com>,
        "open list:ULTRA-WIDEBAND (UWB) SUBSYSTEM:" 
        <linux-usb@...r.kernel.org>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>
Subject: Re: [PATCH v2 04/16] thunderbolt: ACPI: Replace tb_acpi_find_port()
 with acpi_find_child_by_adr()

On Tue, Jun 14, 2022 at 08:25:53PM +0200, Rafael J. Wysocki wrote:
> Hi Mika,
> 
> On Tue, Jun 14, 2022 at 8:07 AM Mika Westerberg
> <mika.westerberg@...ux.intel.com> wrote:
> >
> > Hi Rafael,
> >
> > On Mon, Jun 13, 2022 at 08:11:36PM +0200, Rafael J. Wysocki wrote:
> > > From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > >
> > > Use acpi_find_child_by_adr() to find the child matching a given bus
> > > address instead of tb_acpi_find_port() that walks the list of children
> > > of an ACPI device directly for this purpose and drop the latter.
> > >
> > > Apart from simplifying the code, this will help to eliminate the
> > > children list head from struct acpi_device as it is redundant and it
> > > is used in questionable ways in some places (in particular, locking is
> > > needed for walking the list pointed to it safely, but it is often
> > > missing).
> > >
> > > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > > ---
> > >
> > > v1 -> v2:
> > >    * Drop tb_acpi_find_port() (Heikki, Andy).
> > >    * Change the subject accordingly
> > >
> > > ---
> > >  drivers/thunderbolt/acpi.c |   27 ++++-----------------------
> > >  1 file changed, 4 insertions(+), 23 deletions(-)
> > >
> > > Index: linux-pm/drivers/thunderbolt/acpi.c
> > > ===================================================================
> > > --- linux-pm.orig/drivers/thunderbolt/acpi.c
> > > +++ linux-pm/drivers/thunderbolt/acpi.c
> > > @@ -301,26 +301,6 @@ static bool tb_acpi_bus_match(struct dev
> > >       return tb_is_switch(dev) || tb_is_usb4_port_device(dev);
> > >  }
> > >
> > > -static struct acpi_device *tb_acpi_find_port(struct acpi_device *adev,
> > > -                                          const struct tb_port *port)
> > > -{
> > > -     struct acpi_device *port_adev;
> > > -
> > > -     if (!adev)
> > > -             return NULL;
> > > -
> > > -     /*
> > > -      * Device routers exists under the downstream facing USB4 port
> > > -      * of the parent router. Their _ADR is always 0.
> > > -      */
> > > -     list_for_each_entry(port_adev, &adev->children, node) {
> > > -             if (acpi_device_adr(port_adev) == port->port)
> > > -                     return port_adev;
> > > -     }
> > > -
> > > -     return NULL;
> > > -}
> > > -
> > >  static struct acpi_device *tb_acpi_switch_find_companion(struct tb_switch *sw)
> > >  {
> > >       struct acpi_device *adev = NULL;
> > > @@ -331,7 +311,8 @@ static struct acpi_device *tb_acpi_switc
> > >               struct tb_port *port = tb_port_at(tb_route(sw), parent_sw);
> > >               struct acpi_device *port_adev;
> > >
> > > -             port_adev = tb_acpi_find_port(ACPI_COMPANION(&parent_sw->dev), port);
> > > +             port_adev = acpi_find_child_by_adr(ACPI_COMPANION(&parent_sw->dev),
> > > +                                                port->port);
> > >               if (port_adev)
> > >                       adev = acpi_find_child_device(port_adev, 0, false);
> > >       } else {
> > > @@ -364,8 +345,8 @@ static struct acpi_device *tb_acpi_find_
> > >       if (tb_is_switch(dev))
> > >               return tb_acpi_switch_find_companion(tb_to_switch(dev));
> > >       else if (tb_is_usb4_port_device(dev))
> > > -             return tb_acpi_find_port(ACPI_COMPANION(dev->parent),
> > > -                                      tb_to_usb4_port_device(dev)->port);
> >
> > Can you move the above comment here too?
> 
> Do you mean to move the comment from tb_acpi_find_port() right here or
> before the if (tb_is_switch(dev)) line above?
> 
> I think that tb_acpi_switch_find_companion() would be a better place
> for that comment.  At least it would match the code passing 0 to
> acpi_find_child_device() in there.

Yes, I agree (as long as the comment stays somewhere close ;-))