spi: bcm2835: Fix controller unregister order

The BCM2835 SPI driver uses devm_spi_register_controller() on bind.
As a consequence, on unbind, __device_release_driver() first invokes
bcm2835_spi_remove() before unregistering the SPI controller via
devres_release_all().

This order is incorrect:  bcm2835_spi_remove() tears down the DMA
channels and 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_controller() 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_controller().  Note that
the struct spi_controller as well as the driver-private data are not
freed until after bcm2835_spi_remove() has finished, so accessing them
is safe.

Fixes: 247263dba2 ("spi: bcm2835: use devm_spi_register_master()")
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Cc: stable@vger.kernel.org # v3.13+
Link: https://lore.kernel.org/r/2397dd70cdbe95e0bc4da2b9fca0f31cb94e5aed.1589557526.git.lukas@wunner.de
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-bcm2835.c

@@ -1347,7 +1347,7 @@ static int bcm2835_spi_probe(struct platform_device *pdev)
 		goto out_dma_release;
 	}
 
-	err = devm_spi_register_controller(&pdev->dev, ctlr);
+	err = spi_register_controller(ctlr);
 	if (err) {
 		dev_err(&pdev->dev, "could not register SPI controller: %d\n",
 			err);
@@ -1374,6 +1374,8 @@ static int bcm2835_spi_remove(struct platform_device *pdev)
 
 	bcm2835_debugfs_remove(bs);
 
+	spi_unregister_controller(ctlr);
+
 	/* Clear FIFOs, and disable the HW block */
 	bcm2835_wr(bs, BCM2835_SPI_CS,
 		   BCM2835_SPI_CS_CLEAR_RX | BCM2835_SPI_CS_CLEAR_TX);