Re: [PATCH v2 1/8] driver core: make deferring probe after init optional

[Greg Kroah-Hartman]

On Thu, May 24, 2018 at 12:50:17PM -0500, 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.
> 
> 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");

You really only need dev_warn(), here, right?

thanks,

greg k-h