linux-kernel - Re: [PATCH v1 14/18] driver core: Use device's fwnode to check if it is waiting for suppliers

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Date:   Fri, 20 Nov 2020 18:00:30 -0800
From:   Saravana Kannan <saravanak@...gle.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Marc Zyngier <maz@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tomi Valkeinen <tomi.valkeinen@...com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Grygorii Strashko <grygorii.strashko@...com>,
        "Cc: Android Kernel" <kernel-team@...roid.com>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-efi <linux-efi@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH v1 14/18] driver core: Use device's fwnode to check if it
 is waiting for suppliers

On Mon, Nov 16, 2020 at 8:34 AM Rafael J. Wysocki <rafael@...nel.org> wrote:
>
> On Thu, Nov 5, 2020 at 12:24 AM Saravana Kannan <saravanak@...gle.com> wrote:
> >
> > To check if a device is still waiting for its supplier devices to be
> > added, we used to check if the devices is in a global
> > waiting_for_suppliers list. Since the global list will be deleted in
> > subsequent patches, this patch stops using this check.
>
> My kind of educated guess is that you want to drop
> waiting_for_suppliers and that's why you want to use supplier links
> here.

Yes, and a device would never be added waiting_for_suppliers list.

> >
> > Instead, this patch uses a more device specific check. It checks if the
> > device's fwnode has any fwnode links that haven't been converted to
> > device links yet.
> >
> > Signed-off-by: Saravana Kannan <saravanak@...gle.com>
> > ---
> >  drivers/base/core.c | 18 ++++++++----------
> >  1 file changed, 8 insertions(+), 10 deletions(-)
> >
> > diff --git a/drivers/base/core.c b/drivers/base/core.c
> > index 4ae5f2885ac5..d51dd564add1 100644
> > --- a/drivers/base/core.c
> > +++ b/drivers/base/core.c
> > @@ -51,6 +51,7 @@ static DEFINE_MUTEX(wfs_lock);
> >  static LIST_HEAD(deferred_sync);
> >  static unsigned int defer_sync_state_count = 1;
> >  static DEFINE_MUTEX(fwnode_link_lock);
> > +static bool fw_devlink_is_permissive(void);
> >
> >  /**
> >   * fwnode_link_add - Create a link between two fwnode_handles.
> > @@ -994,13 +995,13 @@ int device_links_check_suppliers(struct device *dev)
> >          * Device waiting for supplier to become available is not allowed to
> >          * probe.
> >          */
> > -       mutex_lock(&wfs_lock);
> > -       if (!list_empty(&dev->links.needs_suppliers) &&
> > -           dev->links.need_for_probe) {
> > -               mutex_unlock(&wfs_lock);
> > +       mutex_lock(&fwnode_link_lock);
> > +       if (dev->fwnode && !list_empty(&dev->fwnode->suppliers) &&
> > +           !fw_devlink_is_permissive()) {
> > +               mutex_unlock(&fwnode_link_lock);
> >                 return -EPROBE_DEFER;
> >         }
> > -       mutex_unlock(&wfs_lock);
> > +       mutex_unlock(&fwnode_link_lock);
> >
> >         device_links_write_lock();
> >
> > @@ -1166,10 +1167,7 @@ static ssize_t waiting_for_supplier_show(struct device *dev,
> >         bool val;
> >
> >         device_lock(dev);
> > -       mutex_lock(&wfs_lock);
> > -       val = !list_empty(&dev->links.needs_suppliers)
> > -             && dev->links.need_for_probe;
> > -       mutex_unlock(&wfs_lock);
>
> Why isn't the lock needed any more?
>
> Or maybe it wasn't needed previously too?

Yeah, I sent a separate patch for dropping this lock [1]. But I didn't
want to wait for that to land to write this series. The lock wasn't
needed in the first place and it was causing a lockdep warning.

>
> > +       val = !list_empty(&dev->fwnode->suppliers);
> >         device_unlock(dev);
> >         return sysfs_emit(buf, "%u\n", val);
> >  }
> > @@ -2226,7 +2224,7 @@ static int device_add_attrs(struct device *dev)
> >                         goto err_remove_dev_groups;
> >         }
> >
> > -       if (fw_devlink_flags && !fw_devlink_is_permissive()) {
> > +       if (fw_devlink_flags && !fw_devlink_is_permissive() && dev->fwnode) {
>
> And why is this change needed?

Because if a device doesn't have a fwnode, it can't ever be waiting on
a supplier. Also, the "show" function dereferences
dev->fwnode->suppliers.

-Saravana

[1] - https://lore.kernel.org/lkml/20201104205431.3795207-1-saravanak@google.com/
Ignore the 1/2 thing. There's only 1 relevant patch.