[PATCH] driver core: Avoid pointless deferred probe attempts

[PATCH] driver core: Avoid pointless deferred probe attempts

[Saravana Kannan]

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.

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)
-- 
2.30.0.478.g8a0d178c01-goog

Re: [PATCH] driver core: Avoid pointless deferred probe attempts

[Rafael J. Wysocki]

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?

>
> 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)
> --

Re: [PATCH] driver core: Avoid pointless deferred probe attempts

[Saravana Kannan]

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)
> > --

Re: [PATCH] driver core: Avoid pointless deferred probe attempts

[Saravana Kannan]

On Thu, Feb 18, 2021 at 9:24 AM Saravana Kannan <saravanak@google.com> wrote:
>
> 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.
>

Btw, this can wait for 5.13. Doesn't need to go into 5.12-rcX.

> > > 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;
> > > +

Also, if you are worried about this check, for now, I can move it
inside device_links_driver_bound() which is the only place that
currently adds a device to the deferred probe list before the driver
is present. But it seemed like a good check in general to have in
driver_deferred_probe_add(), so I put it there.

-Saravana

Re: [PATCH] driver core: Avoid pointless deferred probe attempts

[Geert Uytterhoeven]

Hi Saravana,

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.
>
> Signed-off-by: Saravana Kannan <saravanak@google.com>

Thanks for your patch!

> ---
> Geert,
>
> Can you give this a shot for your I2C DMA issue with fw_devlink=on?

Yes, this makes I2C use DMA again on Salvator-XS during kernel boot-up.

I haven't run any more elaborate tests on other platforms.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Re: [PATCH] driver core: Avoid pointless deferred probe attempts

[Saravana Kannan]

On Tue, Feb 23, 2021 at 2:10 AM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
>
> Hi Saravana,
>
> 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.
> >
> > Signed-off-by: Saravana Kannan <saravanak@google.com>
>
> Thanks for your patch!
>
> > ---
> > Geert,
> >
> > Can you give this a shot for your I2C DMA issue with fw_devlink=on?
>
> Yes, this makes I2C use DMA again on Salvator-XS during kernel boot-up.

Thanks for testing Geert!

> I haven't run any more elaborate tests on other platforms.

Yeah, this change should only go into 5.13 after it gets tested as
part of driver-core-next.

-Saravana

Re: [PATCH] driver core: Avoid pointless deferred probe attempts

[Saravana Kannan]

On Thu, Feb 18, 2021 at 9:24 AM Saravana Kannan <saravanak@google.com> wrote:
>
> 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.
>

Let me know what you think Rafael.

-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)
> > > --