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From:   Saravana Kannan <saravanak@google.com>
Date:   Thu, 18 Feb 2021 09:24:56 -0800
Message-ID: <CAGETcx-M51sy86QGXQpnevXb0AniNPatVJwcM9tRQttVXH5JEg@mail.gmail.com>
Subject: Re: [PATCH] driver core: Avoid pointless deferred probe attempts
To:     "Rafael J. Wysocki" <rafael@kernel.org>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        "Cc: Android Kernel" <kernel-team@android.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Thu, Feb 18, 2021 at 9:18 AM Rafael J. Wysocki <rafael@kernel.org> wrote:
>
> On Thu, Feb 18, 2021 at 12:51 AM Saravana Kannan <saravanak@google.com> wrote:
> >
> > There's no point in adding a device to the deferred probe list if we
> > know for sure that it doesn't have a matching driver. So, check if a
> > device can match with a driver before adding it to the deferred probe
> > list.
>
> What if a matching driver module loads in the meantime?

Driver registration always triggers a match attempt and this flag will
get set at that point. Yes, the user can disable autoprobe, but
that'll block deferred probes too.

-Saravana

>
> >
> > Signed-off-by: Saravana Kannan <saravanak@google.com>
> > ---
> > Geert,
> >
> > Can you give this a shot for your I2C DMA issue with fw_devlink=on?
> >
> > -Saravana
> >
> >  drivers/base/dd.c      | 6 ++++++
> >  include/linux/device.h | 4 ++++
> >  2 files changed, 10 insertions(+)
> >
> > diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> > index 9179825ff646..f18963f42e21 100644
> > --- a/drivers/base/dd.c
> > +++ b/drivers/base/dd.c
> > @@ -123,6 +123,9 @@ static DECLARE_WORK(deferred_probe_work, deferred_probe_work_func);
> >
> >  void driver_deferred_probe_add(struct device *dev)
> >  {
> > +       if (!dev->can_match)
> > +               return;
> > +
> >         mutex_lock(&deferred_probe_mutex);
> >         if (list_empty(&dev->p->deferred_probe)) {
> >                 dev_dbg(dev, "Added to deferred list\n");
> > @@ -726,6 +729,7 @@ static int driver_probe_device(struct device_driver *drv, struct device *dev)
> >         if (!device_is_registered(dev))
> >                 return -ENODEV;
> >
> > +       dev->can_match = true;
> >         pr_debug("bus: '%s': %s: matched device %s with driver %s\n",
> >                  drv->bus->name, __func__, dev_name(dev), drv->name);
> >
> > @@ -829,6 +833,7 @@ static int __device_attach_driver(struct device_driver *drv, void *_data)
> >                 return 0;
> >         } else if (ret == -EPROBE_DEFER) {
> >                 dev_dbg(dev, "Device match requests probe deferral\n");
> > +               dev->can_match = true;
> >                 driver_deferred_probe_add(dev);
> >         } else if (ret < 0) {
> >                 dev_dbg(dev, "Bus failed to match device: %d\n", ret);
> > @@ -1064,6 +1069,7 @@ static int __driver_attach(struct device *dev, void *data)
> >                 return 0;
> >         } else if (ret == -EPROBE_DEFER) {
> >                 dev_dbg(dev, "Device match requests probe deferral\n");
> > +               dev->can_match = true;
> >                 driver_deferred_probe_add(dev);
> >         } else if (ret < 0) {
> >                 dev_dbg(dev, "Bus failed to match device: %d\n", ret);
> > diff --git a/include/linux/device.h b/include/linux/device.h
> > index 7619a84f8ce4..1f9cc1ba78bc 100644
> > --- a/include/linux/device.h
> > +++ b/include/linux/device.h
> > @@ -438,6 +438,9 @@ struct dev_links_info {
> >   * @state_synced: The hardware state of this device has been synced to match
> >   *               the software state of this device by calling the driver/bus
> >   *               sync_state() callback.
> > + * @can_match: The device has matched with a driver at least once or it is in
> > + *             a bus (like AMBA) which can't check for matching drivers until
> > + *             other devices probe successfully.
> >   * @dma_coherent: this particular device is dma coherent, even if the
> >   *             architecture supports non-coherent devices.
> >   * @dma_ops_bypass: If set to %true then the dma_ops are bypassed for the
> > @@ -544,6 +547,7 @@ struct device {
> >         bool                    offline:1;
> >         bool                    of_node_reused:1;
> >         bool                    state_synced:1;
> > +       bool                    can_match:1;
> >  #if defined(CONFIG_ARCH_HAS_SYNC_DMA_FOR_DEVICE) || \
> >      defined(CONFIG_ARCH_HAS_SYNC_DMA_FOR_CPU) || \
> >      defined(CONFIG_ARCH_HAS_SYNC_DMA_FOR_CPU_ALL)
> > --