[PATCH 2/3] spi: pxa2xx: Fix controller unregister order

[Lukas Wunner <lukas@wunner.de>]

The PXA2xx SPI driver uses devm_spi_register_controller() on bind.
As a consequence, on unbind, __device_release_driver() first invokes
pxa2xx_spi_remove() before unregistering the SPI controller via
devres_release_all().

This order is incorrect:  pxa2xx_spi_remove() disables 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 pxa2xx_spi_remove(), 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.

The improper use of devm_spi_register_controller() was introduced in 2013
by commit a807fcd090d6 ("spi: pxa2xx: use devm_spi_register_master()"),
but all earlier versions of the driver going back to 2006 were likewise
broken because they invoked spi_unregister_master() at the end of
pxa2xx_spi_remove(), rather than at the beginning.

Fixes: e0c9905e87ac ("[PATCH] SPI: add PXA2xx SSP SPI Driver")
Link: https://bugzilla.kernel.org/show_bug.cgi?id=206403#c1
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Cc: stable@vger.kernel.org # v2.6.17+
Cc: Tsuchiya Yuto <kitakar@gmail.com>
---
 drivers/spi/spi-pxa2xx.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/spi/spi-pxa2xx.c b/drivers/spi/spi-pxa2xx.c
index 20dcbd35611a..2ecf0d8cd9f7 100644
--- a/drivers/spi/spi-pxa2xx.c
+++ b/drivers/spi/spi-pxa2xx.c
@@ -1885,7 +1885,7 @@ static int pxa2xx_spi_probe(struct platform_device *pdev)
 
 	/* Register with the SPI framework */
 	platform_set_drvdata(pdev, drv_data);
-	status = devm_spi_register_controller(&pdev->dev, controller);
+	status = spi_register_controller(controller);
 	if (status != 0) {
 		dev_err(&pdev->dev, "problem registering spi controller\n");
 		goto out_error_pm_runtime_enabled;
@@ -1917,6 +1917,8 @@ static int pxa2xx_spi_remove(struct platform_device *pdev)
 
 	pm_runtime_get_sync(&pdev->dev);
 
+	spi_unregister_controller(drv_data->controller);
+
 	/* Disable the SSP at the peripheral and SOC level */
 	pxa2xx_spi_write(drv_data, SSCR0, 0);
 	clk_disable_unprepare(ssp->clk);
-- 
2.25.0