linux-kernel - Re: [PATCH v1 04/16] thunderbolt: ACPI: Use acpi_find_child_by

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Date:   Fri, 10 Jun 2022 15:12:49 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Heikki Krogerus <heikki.krogerus@...ux.intel.com>
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>,
        Mika Westerberg <mika.westerberg@...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>
Subject: Re: [PATCH v1 04/16] thunderbolt: ACPI: Use acpi_find_child_by_adr()

On Fri, Jun 10, 2022 at 8:46 AM Heikki Krogerus
<heikki.krogerus@...ux.intel.com> wrote:
>
> On Thu, Jun 09, 2022 at 03:54:40PM +0200, Rafael J. Wysocki wrote:
> > From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> >
> > Instead of walking the list of children of an ACPI device directly
> > in order to find the child matching a given bus address, use
> > acpi_find_child_by_adr() for this purpose.
> >
> > 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>
> > ---
> >  drivers/thunderbolt/acpi.c |    9 +--------
> >  1 file changed, 1 insertion(+), 8 deletions(-)
> >
> > Index: linux-pm/drivers/thunderbolt/acpi.c
> > ===================================================================
> > --- linux-pm.orig/drivers/thunderbolt/acpi.c
> > +++ linux-pm/drivers/thunderbolt/acpi.c
> > @@ -304,8 +304,6 @@ static bool tb_acpi_bus_match(struct 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;
> >
> > @@ -313,12 +311,7 @@ static struct acpi_device *tb_acpi_find_
> >        * 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;
> > +     return acpi_find_child_by_adr(adev, port->port);
> >  }
> >
> >  static struct acpi_device *tb_acpi_switch_find_companion(struct tb_switch *sw)
>
> I don't think you need tb_acpi_find_port() anymore. You can just call
> acpi_find_child_by_ard(ACPI_COMPANION(...), port->port) directly, no?

Technically I can, but I thought that the comment in
tb_acpi_find_port() was worth retaining.