The BCM2835aux SPI driver uses devm_spi_register_master() on bind.
As a consequence, on unbind, __device_release_driver() first invokes
bcm2835aux_spi_remove() before unregistering the SPI controller via
devres_release_all().

This order is incorrect:  bcm2835aux_spi_remove() turns off the SPI
controller, including its interrupts and clock.  The SPI controller
is thus no longer usable.

When the SPI controller is subsequently unregistered, it unbinds all
its slave devices.  If their drivers need to access the SPI bus,
e.g. to quiesce their interrupts, unbinding will fail.

As a rule, devm_spi_register_master() must not be used if the
->remove() hook performs teardown steps which shall be performed
after unbinding of slaves.

Fix by using the non-devm variant spi_register_master().  Note that the
struct spi_master as well as the driver-private data are not freed until
after bcm2835aux_spi_remove() has finished, so accessing them is safe.

Fixes: 1ea29b39 ("spi: bcm2835aux: add bcm2835 auxiliary spi device driver")
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Cc: stable@vger.kernel.org # v4.4+
Cc: Martin Sperl <kernel@martin.sperl.org>
Link: https://lore.kernel.org/r/32f27f4d8242e4d75f9a53f7e8f1f77483b08669.1589557526.git.lukas@wunner.deSigned-off-by: Mark Brown <broonie@kernel.org>