I2C drivers require throttling

[shenki]

The I2C devices have issues when communication happens "too fast".

There was an effort to upstream a generic fix for this issue but it was not merged:

https://lore.kernel.org/all/[email protected]/

Recently some upstream I2C devices got fixes for similar issues. The ucd90320 in 8d655e6 and the max15301 in 1e40633.

IBM carries patches for the UCD9000, PCA955x and MAX31785 drivers using the generic patch that Andrew submitted. This is required for a stable system for witherspoon (ast2500), as well as rainier, everest and bonnell (all ast2600).

In light of multiple devices getting upstream changes to fix this issue, we should propose Andrew's again as a generic solution. If not, we should submit individual changes for the above drivers.

cc @amboar @groeck

(edit: add correct link for the generic fix)