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 <[email protected]> > Signed-off-by: Rob Herring <[email protected]> > --- > 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 >
