Re: [PATCH i2c-tools] TODO: add file and describe items for the 4.5 release

["Brigham Campbell" <me@brighamcampbell.com>]

On Tue Jul 7, 2026 at 6:16 AM MDT, Wolfram Sang wrote:
> You might try busses 0 and 1, too. Some laptops use the Synopsis
> controller.

No such luck, apparently. Busses 0 and 1 each report no devices
attached.

$ sudo i2cdetect -y 0
Warning: Can't use SMBus Quick Write command, will skip some addresses
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:
10:
20:
30: -- -- -- -- -- -- -- --
40:
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60:
70:

Instructing i2cdetect to instead probe using SMBus receive byte shows
the full range, with no devices on synopsis bus 1, but one device bound
to a driver on synopsis 0:

$ sudo i2cdetect -yr 0
[sudo] password for brigham:
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:                         -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- UU -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --

It looks like it's bound to i2c_hid_acpi. No ddr5 temperature sensors in
sight...

> How many? If it is in the 120 range, then every access from i2cdetect
> fails with it.

When I run i2cdetect on the i801 controller, on one invocation I count
111 repetitions of the "SMBus is busy, can't use it!" error once, then
on another invocation I count 112 repetitions. The error condition
appears to be encountered very frequently, but not quite every time.
When the kernel's i2c bus arbitration retry logic kicks in, it appears
to be able to eventually complete the operation successfully before the
i2c core driver code gives up because otherwise I would expect i2cdetect
to exit prematurely and report an error.

Wolfram, if you or any other kernel developers think this may be
indicative of some underlying issue, I'm happy to investigate further
and report back. I'm using a Dell XPS 14 DA14260 laptop.

Cheers!
-- 
Brigham Campbell
https://brighamcampbell.com