While we were busy updating our AMD driver code to accommodate the new SPI controller found in Kabini and Temash, Intel has also changed their SPI interface(s) in a way that required quite some effort to support it in flashrom. A pending patch set is the result of the work of a number of parties and I will shortly explain some details below.
All started with a patch for ChromiumOS’s flashrom fork in fall 2013 that introduced support for Intel’s Bay Trail SoCs which are used in a number of currently shipping or announced Chromebooks. Bay Trail is part of the Silvermont architecture also in other SoCs intended for different use cases like mobile phones (Merrifield and Moorefield) or special-purpose servers (Avoton and Rangeley). At least for the latter two the SPI interface is equivalent to Bay Trail’s. This was handy for Sage when they were developing their support package for Intel’s Mohon Peak (Rangeley reference board) which was upstreamed to the coreboot repository shortly before this blog post was written. They ported the patch to vanilla flashrom, added the necessary PCI IDs and submitted the result to our mailing list at the end of May.
Because we, the flashrom maintainers, are very picky, the code could not be incorporated as is. I took the patch and completely reworked and refactored it so that more code could be shared and we are hopefully better prepared for future variations of similar changes. Additionally, I have also backported the Intel Wildcat Point support that ChromiumOS got already in May.
The major part of my contribution was not simply integrating foreign code, but refactoring and refining it where possible as well as verifying it against datasheets. While digging these numerous datasheets and SPI programming guides I have also fixed the problem of hardware sequencing not working on Lynx Point (and Wildcat Point) as it was reported in March when I had no time to correct it.
All of this is not committed to the main repository yet, but will be soon. It is mostly untested so far and I would very welcome any testers with the respective hardware.