Re: [PATCH v3 1/3] driver core: handle -EPROBE_DEFER from bus_type.match()

[Ulf Hansson]

On 1 December 2015 at 14:34, Marek Szyprowski <m.szyprowski@xxxxxxxxxxx> wrote:
> From: Tomeu Vizoso <tomeu.vizoso@xxxxxxxxxxxxx>
>
> Allow implementations of the match() callback in struct bus_type to
> return errors and if it's -EPROBE_DEFER then queue the device for
> deferred probing.
>
> This is useful to buses such as AMBA in which devices are registered
> before their matching information can be retrieved from the HW
> (typically because a clock driver hasn't probed yet).
>
> Signed-off-by: Tomeu Vizoso <tomeu.vizoso@xxxxxxxxxxxxx>
> [changed if-else code structure, adjusted documentation to match the code]
> Signed-off-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
> ---
>  Documentation/driver-model/porting.txt |  6 ++++--
>  drivers/base/dd.c                      | 24 ++++++++++++++++++++++--
>  include/linux/device.h                 |  2 +-
>  3 files changed, 27 insertions(+), 5 deletions(-)
>
> diff --git a/Documentation/driver-model/porting.txt b/Documentation/driver-model/porting.txt
> index 92d86f7..453053f 100644
> --- a/Documentation/driver-model/porting.txt
> +++ b/Documentation/driver-model/porting.txt
> @@ -340,8 +340,10 @@ comparison:
>
>    int (*match)(struct device * dev, struct device_driver * drv);
>
> -match should return '1' if the driver supports the device, and '0'
> -otherwise.
> +match should return positive value if the driver supports the device,
> +and zero otherwise. It may also return error code (for example
> +-EPROBE_DEFER) if determining that given driver supports the device is
> +not possible.
>
>  When a device is registered, the bus's list of drivers is iterated
>  over. bus->match() is called for each one until a match is found.
> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> index a641cf3..793e915 100644
> --- a/drivers/base/dd.c
> +++ b/drivers/base/dd.c
> @@ -490,6 +490,7 @@ static int __device_attach_driver(struct device_driver *drv, void *_data)
>         struct device_attach_data *data = _data;
>         struct device *dev = data->dev;
>         bool async_allowed;
> +       int ret;
>
>         /*
>          * Check if device has already been claimed. This may
> @@ -500,8 +501,17 @@ static int __device_attach_driver(struct device_driver *drv, void *_data)
>         if (dev->driver)
>                 return -EBUSY;
>
> -       if (!driver_match_device(drv, dev))
> +       ret = driver_match_device(drv, dev);
> +       if (ret == 0) {
> +               /* no match */
>                 return 0;
> +       } else if (ret == -EPROBE_DEFER) {
> +               dev_dbg(dev, "Device match requests probe deferral\n");
> +               driver_deferred_probe_add(dev);
> +       } else if (ret < 0) {
> +               dev_dbg(dev, "Bus failed to match device: %d", ret);
> +               return ret;
> +       } /* ret > 0 means positive match */
>
>         async_allowed = driver_allows_async_probing(drv);
>
> @@ -621,6 +631,7 @@ void device_initial_probe(struct device *dev)
>  static int __driver_attach(struct device *dev, void *data)
>  {
>         struct device_driver *drv = data;
> +       int ret;
>
>         /*
>          * Lock device and try to bind to it. We drop the error
> @@ -632,8 +643,17 @@ static int __driver_attach(struct device *dev, void *data)
>          * is an error.
>          */
>
> -       if (!driver_match_device(drv, dev))
> +       ret = driver_match_device(drv, dev);
> +       if (ret == 0) {
> +               /* no match */
>                 return 0;
> +       } else if (ret == -EPROBE_DEFER) {
> +               dev_dbg(dev, "Device match requests probe deferral\n");
> +               driver_deferred_probe_add(dev);
> +       } else if (ret < 0) {
> +               dev_dbg(dev, "Bus failed to match device: %d", ret);
> +               return ret;
> +       } /* ret > 0 means positive match */
>
>         if (dev->parent)        /* Needed for USB */
>                 device_lock(dev->parent);
> diff --git a/include/linux/device.h b/include/linux/device.h
> index b8f411b..d4e7d1f 100644
> --- a/include/linux/device.h
> +++ b/include/linux/device.h
> @@ -70,7 +70,7 @@ extern void bus_remove_file(struct bus_type *, struct bus_attribute *);
>   * @dev_groups:        Default attributes of the devices on the bus.
>   * @drv_groups: Default attributes of the device drivers on the bus.
>   * @match:     Called, perhaps multiple times, whenever a new device or driver
> - *             is added for this bus. It should return a nonzero value if the
> + *             is added for this bus. It should return a positive value if the

Perhaps add some more information about what happens when returning
error codes!?

>   *             given device can be handled by the given driver.
>   * @uevent:    Called when a device is added, removed, or a few other things
>   *             that generate uevents to add the environment variables.
> --
> 1.9.2
>

Besides the minor nit above, you may add my:

Reviewed-by: Ulf Hansson <ulf.hansson@xxxxxxxxxx>

Kind regards
Uffe
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