Re: i2c-i801 / SMBus timeouts on BayTrail board (U-Boot)

[Jean Delvare <jdelvare@suse.com>]

Hi Stefan,

On ven., 2016-06-24 at 13:57 +0200, Stefan Roese wrote:
> Hi,
> 
> I'm currently trying to use the SMBus on a congatec BayTrail board.
> This works just fine when booting via the original BIOS. But when I
> boot into Linux using U-Boot as bootloader, I get the following
> errors:
> 
> [   81.877121] i801_smbus 0000:00:1f.3: Transaction timeout
> [   81.879228] i801_smbus 0000:00:1f.3: Failed terminating the transaction
> [   81.879320] i801_smbus 0000:00:1f.3: SMBus is busy, can't use it!
> [   81.879373] i801_smbus 0000:00:1f.3: SMBus is busy, can't use it!
> [   81.879421] i801_smbus 0000:00:1f.3: SMBus is busy, can't use it!
> [   81.879496] i801_smbus 0000:00:1f.3: SMBus is busy, can't use it!
> ...
> 
> I checked with an oscilloscope and the SMBus clock is not toggling
> at all in this case. My feeling is, that some basic setup is missing
> in this non-BIOS case. Like some clock enabling. Does anyone of you
> have some idea here?

No immediate idea, sorry. Two ideas:

* Is this problem specific to Baytrail systems, or does i2c-i801 fail on
all U-Boot systems?

* Did you try comparing the PCI configuration space of the SMBus device
between original BIOS boot (working) and U-Boot boot (not working)?

-- 
Jean Delvare
SUSE L3 Support