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Gerrit Code Review

Hands-on: Read PCI register

Hands-on: Read PCI register

• Write a single function
  • Dump the following PCI registers of device 00:14.0
    • 0x02
    • 0x10
  • Put the function into a separate file
  • The function must be called in romstage and in ramstage init phase
• Use the existing functions in mainboard/ocp/weedge100s
• Use as much defines as possible
• Write down the dumped register values for
  • romstage
  • ramstage

Task:

Hands-on: Read PCI register

• Add a new source file and header
• Include the added file into the build system
• Search for a function that does read from PCI register space
• Write your own function
• Call your function from romstage and ramstage

Hint:

• special define __SIMPLE_DEVICE__
  • always set in romstage on x86
  • optional use in ramstage
  • changes function prototype of PCI functions

30 min

Hands-on: Read raw values from FMAP region

Hands-on: Read raw values from FMAP region

• Locate the "COREBOOT" FMAP region
• Mmap the region and print the first 8 bytes as ASCII string
• Print an error if you don't find the FMAP region
• On sucess write down the dumped value

Task:

20 min

Hands-on: Read cbmem console

Hands-on: Read the cbmem console in Linux

• Use the wedge100s as target
• Read the cbmem console using Linux's sysfs
• Write down the second line after "coreboot romstage starting..."

Task:

15 min

Hands-on: Read the cbmem console in Linux

• Boot into the Linux system with SeaBIOS

Hint:

CTF

Background

The Wedge100s SoC implementation is utterly broken:

• UPD is currently not working on FSP Broadwell DE but is used to configure the FSP dynamically from coreboot
• No SPI console support for broadwell DE
• The Vital Product Data is a Google feature and not available without Chrome OS support. But it is required by the LinuxBoot payload in conjunction with systemboot.
• In the current Wedge100s mainboard implementation is missing the MRC cache which is required for fast boot cycles.  

MRC cache

• Memory Reference Code
• Ripped out of FSP by Google to get rid of BLOBs
• Idea:
  • Backup DRAM training values in flash
  • Restore training values on S3 resume and normal boot
  • Old platforms did use NVRAM instead
  • Old method: mrc.cache in CBFS
  • New method: FMAP region
• Nowadays:
  • Additional configuration values (PEG)
  • Written to flash in ramstage
  • Write protected adter ramstage
• Decreased boot times: 10 seconds -> 0.1 second (2Channel DDR3)

Hands-on: Add FMAP MRC cache

Hands-on: Add FMAP MRC cache

• Include a RW_MRC_CACHE region in the FMAP
• Decrease the size of COREBOOT(CBFS)
• Boot the wedge100s at least two times
• Compare the timestamps to make sure there's a difference in boot time
• Write down the offset of UNIFIED_MRC_CACHE and the size of COREBOOT(CBFS)

Task:

30 min

Hands-on: Add FMAP MRC cache

• Have a look at CHROMEOS enabled boards

Hint:

Hands-on: Fix SPI console

Hands-on: Fix SPI console

Task:

• Add CONSOLE to FMAP
• Fix linking errors
• Fix compiler errors
• Make it accept globals in romstage
• Build SPI console enabled coreboot.rom for wedge100s
• Run with SPI console enabled on wedge100s

Problem:

• SPI console doesn't work on fsp_broadwell_de

Hands-on: Fix SPI console

Hint:

• Add "CONSOLE" region to FMAP
• Enable SPI flash console
• Run make to find missing source file include
• Add source file
• Add headers
• Replaces defines that it compiles in all stages
• Add defines for globals in romstage

45 min

Hands-on: Get VPD running on Wedge100s

• Vital Product Data
• Key Value Store
• FMAP partitions:
  • RO_VPD : Stores machine-specific information, like the mainboard serial number and MAC address.
  • RW_VPD : Stores all data that will be updated after a device leaves the factory.

Hands-on: Get VPD running on Wedge100s

• Modifiy VPD using the vpd tool

Hands-on: Get VPD running on Wedge100s

./vpd -f build/coreboot.rom -O -i RO_VPD -s "Boot0000"='{"device_path": "/dev/sda1", "bc_file": "/boot/bc.img", "bc_name": "test"}'

Task:

Hands-on: Get VPD running on Wedge100s

• Move VPD code to src/drivers/vpd and adapt it to fit as a driver
• Add "select VPD" to the ChromeOS kconfig option
• Add "select VPD" to Wedge100s kconfig
• Add VPD_RO and VPD_RW to FMAP
• Add RO VPD using vpd tool
• Use LinuxBoot to access the VPD

120 min