Hi All,

I am afraid that commit 21653a4181ff ("i2c: core: Call i2c_acpi_install_space_handler() before i2c_acpi_register_devices()") which is in 5.9 and was also added to 5.8.13 (and possible other stable series releases) causes a regression on some devices including on the Microsoft Surface Go 2 (and possibly also the Go 1) where the system no longer boots.

Before the troublesome commit the ACPI related i2c core code looked like this:

/* create pre-declared device nodes */ of_i2c_register_devices(adap); i2c_acpi_register_devices(adap); i2c_acpi_install_space_handler(adap);

if (...

The trouble some commit changed this to:

/* create pre-declared device nodes */ of_i2c_register_devices(adap); i2c_acpi_install_space_handler(adap); i2c_acpi_register_devices(adap);

if (...

The goal here was to only move the acpi_install_address_space_handler() which is wrapped by i2c_acpi_install_space_handler() which should be pretty safe. But as Maximilian Luz' sharp eyes pointed out while debugging the regression, i2c_acpi_install_space_handler() does more, it also contains a call to acpi_walk_dep_device_list() at the end. Which I missed and which is causing the trouble we are seeing now.

The original code flow looked like this:

1. i2c_acpi_register_devices() 1.1 Create ACPI declared i2c_clients for adap 2. i2c_acpi_install_space_handler(adap); 2.1 acpi_install_address_space_handler() 2.2 acpi_walk_dep_device_list()

And after the troublesome commit it now looks like this:

1. i2c_acpi_install_space_handler(adap); 1.1 acpi_install_address_space_handler() 1.2 acpi_walk_dep_device_list() 2. i2c_acpi_register_devices() 2.1 Create ACPI declared i2c_clients for adap

Notice that the acpi_walk_dep_device_list() now happens before the i2c_clients below this adapter are created.

The patch in this 1 patch series fixes this by moving the acpi_walk_dep_device_list() call to the end of i2c_acpi_register_devices(), partly restoring the original order, so that we now get:

1. i2c_acpi_install_space_handler(adap); 1.1 acpi_install_address_space_handler() 2. i2c_acpi_register_devices() 2.1 Create ACPI declared i2c_clients for adap 2.2 acpi_walk_dep_device_list()

So we end up calling acpi_walk_dep_device_list() last again, as before.

Sorry for missing this the first time around.

Wolfram, can we get this queued up to go to Linus soonish ?

Greg, in essence this is a partial revert of the trouble some commit. With the 2 combined acpi_walk_dep_device_list() is called last again, while still doing the acpi_install_address_space_handler() call earlier.

Since this is a somewhat nasty regression and since the poor timing wrt the merge-window, I was hoping that you would be willing to make an exception and pick up this fix before it hits Linus' tree?

The alternative would be to revert this now and then pick up both again later, when the fix has landed in Linus' tree. The problem with that is that reverting the original troublesome commit will regress all these bugs:

https://bugzilla.redhat.com/show_bug.cgi?id=1842039 https://bugzilla.redhat.com/show_bug.cgi?id=1871793 https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1861610

Regards,

Hans