common: add initial barebox deep-probe support

The barebox 'deep probe' or 'probe on demand' mechanism is the answer of
unwanted -EPROBE_DEFER failures. The EPROBE_DEFER error code was
introduced by commit ab3da15bc14c ("base: Introduce deferred probing")
and since then it causes a few problems.

The error is returned if either the device is not yet present or the
driver is not yet registered. This makes sense on linux systems where
modules and hot-plug devices are used very often but not for barebox.
The module support is rarely used and devices aren't hot pluggable.

The current barebox behaviour populates all devices before the drivers
are registered so all devices are present during the driver
registration. So the driver probe() function gets called immediately
after the driver registration and causes the -EPROBE_DEFER error if this
driver depends on an other not yet registered driver.

To get rid of the EPROBE_DEFER error code we need to reorder the device
population and the driver registration. All drivers must be registered
first. In an ideal world all driver can be registered by the same
initcall level. Then devices are getting populated which causes calling
the driver probe() function but this time resources/devices are created
on demand if not yet available.

Dependencies between devices are normally expressed as references to
other device nodes. With deep probe barebox provides helper functions
which take a device node and probe the device behind that node if
necessary. This means instead of returning -EPROBE_DEFER, we can now
make the desired resources available once we need them.

If the resource can't be created we are returning -ENODEV since we are
not supporting hot-plugging. Dropping EPROBE_DEFER is the long-term
goal, avoid initcall shifting is the short-term goal.

Call it deep-probe since the on-demand device creation can create very
deep stacks. This commit adds the initial support for: spi, i2c, reset,
regulator, gpio and clk resource on-demand creation. The deep-probe
mechanism must be enabled for each board to avoid breaking changes using
deep_probe_enable(). This can be changed later after all boards are
converted to the new mechanism.

Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
Link: https://lore.pengutronix.de/20201021115813.31645-8-m.felsch@pengutronix.de
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Link: https://lore.barebox.org/20210625072540.32717-10-s.hauer@pengutronix.de
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

1 files changed, 2 insertions, 0 deletions

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 8421d9d7c1..d1d3bdcc41 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -107,6 +107,8 @@ struct spi_device *spi_new_device(struct spi_controller *ctrl,
 	if (status)
 		goto fail;
 
+	chip->device_node->dev = &proxy->dev;
+
 	return proxy;
 fail:
 	free(proxy);