[PATCH 2/2][SRU][B][OEM-B] i2c: i2c-designware-platdrv: Always use a dynamic adapter number

AceLan Kao acelan.kao at canonical.com
Wed Jul 3 03:16:15 UTC 2019

From: Hans de Goede <hdegoede at redhat.com>

BugLink: https://bugs.launchpad.net/bugs/1835150

Before this commit the i2c-designware-platdrv assumes that if the pdev
has an apci-companion it should use a dynamic adapter-nr and it sets
adapter->nr to -1, otherwise it will use pdev->id as adapter->nr.

There are 3 ways how platform_device-s to which i2c-designware-platdrv
will bind can be instantiated:

1) Through of / devicetree
2) Through ACPI enumeration
3) Explicitly instantiated through platform_device_create + add

1) In case of devicetree-instantiation the drivers/of code always sets
pdev->id to PLATFORM_DEVID_NONE, which is -1 so in this case both paths
to set adapter->nr end up doing the same thing.

2) In case of ACPI instantiation the device will always have an
ACPI-companion, so we are already using dynamic adapter-nrs.

3) There are 2 places manually instantiating a designware_i2c platform_dev:

In the intel_quark_i2c_gpio.c case pdev->id is always 0, so switching to
dynamic adapter-nrs here could lead to the bus-number no longer being
stable, but the quark X1000 only has 1 i2c-controller, which will also
be assigned bus-number 0 when using dynamic adapter-nrs.

In the intel-lpss.c case intel_lpss_probe() is called from either
intel-lpss-acpi.c in which case there always is an ACPI-companion, or
from intel-lpss-pci.c. In most cases devices handled by intel-lpss-pci.c
also have an ACPI-companion, so we use a dynamic adapter-nr. But in some
cases the ACPI-companion is missing and we would use pdev->id (allocated
from intel_lpss_devid_ida). Devices which use the intel-lpss-pci.c code
typically have many i2c busses, so using pdev->id in this case may lead
to a bus-number conflict, triggering a WARN(id < 0, "couldn't get idr")
in i2c-core-base.c causing an oops an the adapter registration to fail.
So in this case using non dynamic adapter-nrs is actually undesirable.

One machine on which this oops was triggering is the Apollo Lake based
Acer TravelMate Spin B118.

TL;DR: Switching to always using dynamic adapter-numbers does not make
any difference in most cases and in the one case where it does make a
difference the behavior change is desirable because the old behavior
caused an oops.

BugLink: https://bugzilla.redhat.com/show_bug.cgi?id=1687065
Signed-off-by: Hans de Goede <hdegoede at redhat.com>
Acked-by: Andy Shevchenko <andriy.shevchenko at linux.intel.com>
Acked-by: Jarkko Nikula <jarkko.nikula at linux.intel.com>
Signed-off-by: Wolfram Sang <wsa at the-dreams.de>
(cherry picked from commit cd86d1403bb4c80e443d736b2a692cbf68a9f471)
Signed-off-by: AceLan Kao <acelan.kao at canonical.com>
 drivers/i2c/busses/i2c-designware-platdrv.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/drivers/i2c/busses/i2c-designware-platdrv.c b/drivers/i2c/busses/i2c-designware-platdrv.c
index 7bb147cface3..662704541acd 100644
--- a/drivers/i2c/busses/i2c-designware-platdrv.c
+++ b/drivers/i2c/busses/i2c-designware-platdrv.c
@@ -369,10 +369,7 @@ static int dw_i2c_plat_probe(struct platform_device *pdev)
 	adap->class = I2C_CLASS_DEPRECATED;
 	ACPI_COMPANION_SET(&adap->dev, ACPI_COMPANION(&pdev->dev));
 	adap->dev.of_node = pdev->dev.of_node;
-	if (has_acpi_companion(&pdev->dev))
-		adap->nr = -1;
-	else
-		adap->nr = pdev->id;
+	adap->nr = -1;
 	/* The code below assumes runtime PM to be disabled. */

More information about the kernel-team mailing list