Re: 5.11-rc device reordering breaks ThinkPad rmi4 suspend

[Hugh Dickins <hughd@google.com>]

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On Mon, 11 Jan 2021, Thierry Reding wrote:
> On Sun, Jan 10, 2021 at 08:44:13PM -0800, Hugh Dickins wrote:
> > 
> > Synaptics RMI4 SMBus touchpad on ThinkPad X1 Carbon (5th generation)
> > fails to suspend when running 5.11-rc kernels: bisected to 
> > 5b6164d3465f ("driver core: Reorder devices on successful probe"),
> > and reverting that fixes it.  dmesg.xz attached, but go ahead and ask
> > me to switch on a debug option to extract further info if that may help.
...
> 
> I think what might be happening here is that the offending patch causes
> some devices to be reordered in a way different to how they were ordered
> originally and the rmi4 driver currently depends on that implicit order.

Yes, all that you explained makes good sense, thanks.

> I'm not familiar with how exactly rmi4 works, so I'll have to do
> some digging to hopefully pinpoint exactly what's going wrong here.
> 
> In the meantime, it would be useful to know what exactly the I2C
> hierarchy looks like. For example, what's the I2C controller that the
> RMI4 device is hooked up to. According to the above, that's I2C bus 6,
> so you should be able to find out some details about it by inspecting
> the corresponding sysfs nodes:
> 
> 	$ ls -l /sys/class/i2c-adapter/i2c-6/
> 	$ cat /sys/class/i2c-adapter/i2c-6/name
> 	$ ls -l /sys/class/i2c-adapter/i2c-6/device/

That's curious: I don't even have a /sys/class/i2c-adapter directory.

(And I did wonder if you meant to say "smbus" rather than "i2c",
though I don't have any /sys/class/smbus* either: I have no notion
of the relationship between i2c and smbus, but I thought the failing
write_block calls were the ones in rmi_smbus.c rather than rmi_i2c.c.)

I've attached compressed output of "find /sys/bus /sys/class | sort":
/sys/bus looked more relevant than /sys/class, maybe it will help
point in the right direction?

And in case it's relevant, maybe I should mention that this is a
non-modular, all-built-in kernel.

But as I said to Rafael, my touchpad can wait: the wider ordering
discussion is much more important.

Hugh

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