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

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Date:   Thu, 18 Feb 2021 18:18:27 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Saravana Kannan <saravanak@...gle.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        "Cc: Android Kernel" <kernel-team@...roid.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] driver core: Avoid pointless deferred probe attempts

On Thu, Feb 18, 2021 at 12:51 AM Saravana Kannan <saravanak@...gle.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@...gle.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)
> --