Re: [PATCH 1/2] i2c: i2c-designware-platdrv: Allow a dynamic adap. nr without an ACPI fwnode

From: Jarkko Nikula
Date: Tue Mar 12 2019 - 10:47:53 EST


On 3/11/19 1:22 PM, Hans de Goede wrote:
Before this commit the i2c-designware-platdrv assumes that if the pdev
has an apci-companion it should use a dynamic adapter-nr and otherwise
it will use pdev->id as adapter-nr.

On some devices e.g. the Apollo Lake using Acer TravelMate Spin B118,
some of the LPSS i2c-adapters are enumerated through PCI and do not have
an ACPI fwnode. These devices are handled as mfd devices so they end up
using the i2c-designware-platdrv driver.

This results in the i2c-adapter being registered with the mfd generated
pdev->id as adapter-nr, which conflicts with existing adapters, triggering
a WARN(id < 0, "couldn't get idr") in i2c-core-base.c and causing the
adapter registration to fail.

I went thinking would we get a regression if we switch the i2c-designware-platdrv to dynamic numbering unconditionally?

Only drivers/mfd/intel-lpss.c and drivers/mfd/intel_quark_i2c_gpio.c register platform device "i2c_designware" and otherwise in the driver itself for known ACPI IDs and device tree bindings.

Things should be fine for ACPI cases if slave devices are also described in ACPI tables. As far as I've understood with device tree matching adapter number is irrelevant in slave device registration?

Andy: could you tell by commit 918fe70cf475 ("mfd: intel_quark_i2c_gpio: support devices behind i2c bus") are those devices described in ACPI or in some i2c_board_infos with referring to fixed adapter number either in or out of kernel tree code?

Then drivers/platform/chrome/chromeos_laptop.c is the only code searching for adapter named as "Synopsys DesignWare I2C adapter" without assuming any fixed adapter numbering.

What's unclear to me can there be device tree cases where i2c-designware probing comes with pdev->id not starting from zero or in different order? I.e. would it make difference do we use pdev->id or dynamic adapter numbering?