spi: dw: Fix controller unregister order

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

This order is incorrect:  dw_spi_remove_host() shuts down the chip,
rendering the SPI bus inaccessible even though the SPI controller is
still registered.  When the SPI controller is subsequently unregistered,
it unbinds all its slave devices.  Because their drivers cannot access
the SPI bus, e.g. to quiesce interrupts, the slave devices may be left
in an improper state.

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

Fix by reverting to the non-devm variant of spi_register_controller().

An alternative approach would be to use device-managed functions for all
steps in dw_spi_remove_host(), e.g. by calling devm_add_action_or_reset()
on probe.  However that approach would add more LoC to the driver and
it wouldn't lend itself as well to backporting to stable.

Fixes: 04f421e7 ("spi: dw: use managed resources")
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: stable@vger.kernel.org # v3.14+
Cc: Baruch Siach <baruch@tkos.co.il>
Link: https://lore.kernel.org/r/3fff8cb8ae44a9893840d0688be15bb88c090a14.1590408496.git.lukas@wunner.deSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-dw.c

@@ -526,7 +526,7 @@ int dw_spi_add_host(struct device *dev, struct dw_spi *dws)
 		}
 	}
 
-	ret = devm_spi_register_controller(dev, master);
+	ret = spi_register_controller(master);
 	if (ret) {
 		dev_err(&master->dev, "problem registering spi master\n");
 		goto err_dma_exit;
@@ -550,6 +550,8 @@ void dw_spi_remove_host(struct dw_spi *dws)
 {
 	dw_spi_debugfs_remove(dws);
 
+	spi_unregister_controller(dws->master);
+
 	if (dws->dma_ops && dws->dma_ops->dma_exit)
 		dws->dma_ops->dma_exit(dws);