On Thu 24 May 10:50 PDT 2018, Rob Herring wrote:
> Deferred probe will currently wait forever on dependent devices to probe,
> but sometimes a driver will never exist. It's also not always critical for
> a driver to exist. Platforms can rely on default configuration from the
> bootloader or reset defaults for things such as pinctrl and power domains.
> This is often the case with initial platform support until various drivers
> get enabled. There's at least 2 scenarios where deferred probe can render
> a platform broken. Both involve using a DT which has more devices and
> dependencies than the kernel supports. The 1st case is a driver may be
> disabled in the kernel config. The 2nd case is the kernel version may
> simply not have the dependent driver. This can happen if using a newer DT
> (provided by firmware perhaps) with a stable kernel version.
>
> Subsystems or drivers may opt-in to this behavior by calling
> driver_deferred_probe_check_init_done() instead of just returning
> -EPROBE_DEFER. They may use additional information from DT or kernel's
> config to decide whether to continue to defer probe or not.
>
For builtin drivers this still looks reasonable.
But I would like to have an additional clarification here stating that
drivers that might be targeted by this query must not be compiled as
modules.
And I would prefer to see an ack from e.g. Arnd that arm-soc is okay
that we drop "tristate" on drivers affected by this; e.g. if we put this
in the pinctrl core then all pinctrl drivers should be "bool" and so
should any i2c, ssbi and spmi buses and drivers be.
Regards,
Bjorn
> Cc: Alexander Graf <agraf@xxxxxxx>
> Signed-off-by: Rob Herring <robh@xxxxxxxxxx>
> ---
> drivers/base/dd.c | 17 +++++++++++++++++
> include/linux/device.h | 2 ++
> 2 files changed, 19 insertions(+)
>
> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> index c9f54089429b..d6034718da6f 100644
> --- a/drivers/base/dd.c
> +++ b/drivers/base/dd.c
> @@ -226,6 +226,16 @@ void device_unblock_probing(void)
> driver_deferred_probe_trigger();
> }
>
> +int driver_deferred_probe_check_init_done(struct device *dev, bool optional)
> +{
> + if (optional && initcalls_done) {
> + dev_WARN(dev, "ignoring dependency for device, assuming no driver");
> + return -ENODEV;
> + }
> +
> + return -EPROBE_DEFER;
> +}
> +
> /**
> * deferred_probe_initcall() - Enable probing of deferred devices
> *
> @@ -240,6 +250,13 @@ static int deferred_probe_initcall(void)
> /* Sort as many dependencies as possible before exiting initcalls */
> flush_work(&deferred_probe_work);
> initcalls_done = true;
> +
> + /*
> + * Trigger deferred probe again, this time we won't defer anything
> + * that is optional
> + */
> + driver_deferred_probe_trigger();
> + flush_work(&deferred_probe_work);
> return 0;
> }
> late_initcall(deferred_probe_initcall);
> diff --git a/include/linux/device.h b/include/linux/device.h
> index 477956990f5e..f3dafd44c285 100644
> --- a/include/linux/device.h
> +++ b/include/linux/device.h
> @@ -334,6 +334,8 @@ struct device *driver_find_device(struct device_driver *drv,
> struct device *start, void *data,
> int (*match)(struct device *dev, void *data));
>
> +int driver_deferred_probe_check_init_done(struct device *dev, bool optional);
> +
> /**
> * struct subsys_interface - interfaces to device functions
> * @name: name of the device function
> --
> 2.17.0
>
--
To unsubscribe from this list: send the line "unsubscribe devicetree" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
