i2c: i2c-designware-platdrv: Always use a dynamic adapter number

jwrdegoede · Wolfram Sang · commit cd86d1403bb4 · 2019-03-13T18:07:10.000+01:00
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: drivers/mfd/intel_quark_i2c_gpio.c drivers/mfd/intel-lpss.c 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@redhat.com> Acked-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com> Acked-by: Jarkko Nikula <jarkko.nikula@linux.intel.com> Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
diff --git a/drivers/i2c/busses/i2c-designware-platdrv.c b/drivers/i2c/busses/i2c-designware-platdrv.c
@@ -363,10 +363,7 @@ 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;
 
 	dev_pm_set_driver_flags(&pdev->dev,
 				DPM_FLAG_SMART_PREPARE |
