Re: [PATCH] driver: core: Allow subsystems to continue deferring probe

[Ulf Hansson]

+ Rob

On Wed, 5 Jun 2019 at 16:23, Thierry Reding <thierry.reding@xxxxxxxxx> wrote:
>
> From: Thierry Reding <treding@xxxxxxxxxx>
>
> Some subsystems, such as pinctrl, allow continuing to defer probe
> indefinitely. This is useful for devices that depend on resources
> provided by devices that are only probed after the init stage.
>
> One example of this can be seen on Tegra, where the DPAUX hardware
> contains pinmuxing controls for pins that it shares with an I2C
> controller. The I2C controller is typically used for communication
> with a monitor over HDMI (DDC). However, other instances of the I2C
> controller are used to access system critical components, such as a
> PMIC. The I2C controller driver will therefore usually be a builtin
> driver, whereas the DPAUX driver is part of the display driver that
> is loaded from a module to avoid bloating the kernel image with all
> of the DRM/KMS subsystem.
>
> In this particular case the pins used by this I2C/DDC controller
> become accessible very late in the boot process. However, since the
> controller is only used in conjunction with display, that's not an
> issue.
>
> Unfortunately the driver core currently outputs a warning message
> when a device fails to get the pinctrl before the end of the init
> stage. That can be confusing for the user because it may sound like
> an unwanted error occurred, whereas it's really an expected and
> harmless situation.
>
> In order to eliminate this warning, this patch allows callers of the
> driver_deferred_probe_check_state() helper to specify that they want
> to continue deferring probe, regardless of whether we're past the
> init stage or not. All of the callers of that function are updated
> for the new signature, but only the pinctrl subsystem passes a true
> value in the new persist parameter if appropriate.
>
> Signed-off-by: Thierry Reding <treding@xxxxxxxxxx>

Overall this looks good to me. I guess Greg prefers a separate
function, which sets a flag for the device to switch to this new
behavior. That seems like a reasonable change to make and avoids
changing calls to driver_deferred_probe_check_state().

Kind regards
Uffe

> ---
>  drivers/base/dd.c            | 17 ++++++++++++-----
>  drivers/base/power/domain.c  |  2 +-
>  drivers/iommu/of_iommu.c     |  2 +-
>  drivers/pinctrl/devicetree.c | 10 ++++++----
>  include/linux/device.h       |  2 +-
>  5 files changed, 21 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> index 0df9b4461766..25ffbadf4187 100644
> --- a/drivers/base/dd.c
> +++ b/drivers/base/dd.c
> @@ -238,23 +238,30 @@ __setup("deferred_probe_timeout=", deferred_probe_timeout_setup);
>  /**
>   * driver_deferred_probe_check_state() - Check deferred probe state
>   * @dev: device to check
> + * @persist: Boolean flag indicating whether drivers should keep trying to
> + *   probe after built-in drivers have had a chance to probe. This is useful
> + *   for built-in drivers that rely on resources provided by modular drivers.
>   *
>   * Returns -ENODEV if init is done and all built-in drivers have had a chance
> - * to probe (i.e. initcalls are done), -ETIMEDOUT if deferred probe debug
> - * timeout has expired, or -EPROBE_DEFER if none of those conditions are met.
> + * to probe (i.e. initcalls are done) and unless persist is set, -ETIMEDOUT if
> + * deferred probe debug timeout has expired, or -EPROBE_DEFER if none of those
> + * conditions are met.
>   *
>   * Drivers or subsystems can opt-in to calling this function instead of directly
>   * returning -EPROBE_DEFER.
>   */
> -int driver_deferred_probe_check_state(struct device *dev)
> +int driver_deferred_probe_check_state(struct device *dev, bool persist)
>  {
>         if (initcalls_done) {
>                 if (!deferred_probe_timeout) {
>                         dev_WARN(dev, "deferred probe timeout, ignoring dependency");
>                         return -ETIMEDOUT;
>                 }
> -               dev_warn(dev, "ignoring dependency for device, assuming no driver");
> -               return -ENODEV;
> +
> +               if (!persist) {
> +                       dev_warn(dev, "ignoring dependency for device, assuming no driver");
> +                       return -ENODEV;
> +               }
>         }
>         return -EPROBE_DEFER;
>  }
> diff --git a/drivers/base/power/domain.c b/drivers/base/power/domain.c
> index 33c30c1e6a30..effa5276a773 100644
> --- a/drivers/base/power/domain.c
> +++ b/drivers/base/power/domain.c
> @@ -2423,7 +2423,7 @@ static int __genpd_dev_pm_attach(struct device *dev, struct device *base_dev,
>                 mutex_unlock(&gpd_list_lock);
>                 dev_dbg(dev, "%s() failed to find PM domain: %ld\n",
>                         __func__, PTR_ERR(pd));
> -               return driver_deferred_probe_check_state(base_dev);
> +               return driver_deferred_probe_check_state(base_dev, false);
>         }
>
>         dev_dbg(dev, "adding to PM domain %s\n", pd->name);
> diff --git a/drivers/iommu/of_iommu.c b/drivers/iommu/of_iommu.c
> index f04a6df65eb8..70f3946b088a 100644
> --- a/drivers/iommu/of_iommu.c
> +++ b/drivers/iommu/of_iommu.c
> @@ -117,7 +117,7 @@ static int of_iommu_xlate(struct device *dev,
>          * a proper probe-ordering dependency mechanism in future.
>          */
>         if (!ops)
> -               return driver_deferred_probe_check_state(dev);
> +               return driver_deferred_probe_check_state(dev, false);
>
>         return ops->of_xlate(dev, iommu_spec);
>  }
> diff --git a/drivers/pinctrl/devicetree.c b/drivers/pinctrl/devicetree.c
> index f7e354f85518..c808bf567d24 100644
> --- a/drivers/pinctrl/devicetree.c
> +++ b/drivers/pinctrl/devicetree.c
> @@ -111,13 +111,15 @@ static int dt_to_map_one_config(struct pinctrl *p,
>
>                 np_pctldev = of_get_next_parent(np_pctldev);
>                 if (!np_pctldev || of_node_is_root(np_pctldev)) {
> +                       bool persist = false;
> +
>                         of_node_put(np_pctldev);
> -                       ret = driver_deferred_probe_check_state(p->dev);
>                         /* keep deferring if modules are enabled unless we've timed out */
> -                       if (IS_ENABLED(CONFIG_MODULES) && !allow_default && ret == -ENODEV)
> -                               ret = -EPROBE_DEFER;
> +                       if (IS_ENABLED(CONFIG_MODULES) && !allow_default)
> +                               persist = true;
>
> -                       return ret;
> +                       return driver_deferred_probe_check_state(p->dev,
> +                                                                persist);
>                 }
>                 /* If we're creating a hog we can use the passed pctldev */
>                 if (hog_pctldev && (np_pctldev == p->dev->of_node)) {
> diff --git a/include/linux/device.h b/include/linux/device.h
> index e0649f6adf2e..ecf59dfcbfb7 100644
> --- a/include/linux/device.h
> +++ b/include/linux/device.h
> @@ -340,7 +340,7 @@ struct device *driver_find_device(struct device_driver *drv,
>                                   int (*match)(struct device *dev, void *data));
>
>  void driver_deferred_probe_add(struct device *dev);
> -int driver_deferred_probe_check_state(struct device *dev);
> +int driver_deferred_probe_check_state(struct device *dev, bool persist);
>
>  /**
>   * struct subsys_interface - interfaces to device functions
> --
> 2.21.0
>