Patch merged into coreboot/master: drivers/pc80: Add optional spinlock for nvram CBFS access

the following patch was just integrated into master:
commit 7b22d84d55386ee422fa77c1d8bce9dddeaaa231
Author: Timothy Pearson 
Date:   Fri Aug 28 19:52:05 2015 -0500

drivers/pc80: Add optional spinlock for nvram CBFS access

When enabling the IOMMU on certain systems dmesg is spammed with I/O page faults like the following:
    AMD-Vi: Event logged [IO_PAGE_FAULT device=00:14.0 domain=0x000a address=0x000000fdf9103300 flags=0x0030]

Decoding the faulting address:
    0x000000fdf9103300
            fdf91x          Hypertransport system management region
                  33        SysMgtCmd (System Management Command) = 0x33
                  3         Base Command Type = 0x3: STPCLK (Stop Clock request)
                   3        SMAF (System Management Action Field) = [3:1] = 0x1
                   1        Signal State Bit Map = [0] = 0x1

Therefore, the error appears to be triggered by an upstream C1E request.

This was eventually traced to concurrent access to the SP5100's SPI Flash controller by
    multiple APs during startup.  Calls to the nvram read functions get_option and read_option
    call CBFS functions, which in turn make near-simultaneous requests to the SPI Flash
    controller, thus placing the SP5100 in an invalid state.  This limitation is not documented
    in any public AMD errata, and was only discovered through considerable debugging effort.

Change-Id: I4e61b1ab767b1b7958ac7c1cf20eee41d2261bef
    Signed-off-by: Timothy Pearson 
    Reviewed-on: https://review.coreboot.org/12061
    Tested-by: build bot (Jenkins)
    Reviewed-by: Martin Roth

See https://review.coreboot.org/12061 for details.

-gerrit