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flashrom

Overview

Flashrom is a userspace utility we use primarily to update host (AP/PCH) firmware, but can also be used to update firmware on other components such as ECs. it can be run both on the target machine (field updates) or on a user's workstation to flash via an external programmer such as Servo, Dediprog SF100, Bus Pirate and more.

Flashrom is an open-source project hosted at http://flashrom.org. The version which is used in Chrome OS devices and in the CrOS SDK is a forked version with some CrOS-specific modifications. It can be found at the following URL: https://chromium.googlesource.com/chromiumos/third_party/flashrom/

Basic Usage

This section will cover basic command-line usage. The most commonly used command-line switches are:

-r | --read                       read flash and save to file

-w | --write                      write to flash

-p | --programmer <name>[:<param] specify the programmer device and parameters


The "-p" argument tells us which programmer interface we are targeting. Examples include "host", "ec", or "ft2232_spi:type=servo-v2" (see section on Servo below). For a full listing of command-line switches, use -h or --help.


The following commands have to do with write-protection:

--wp-status                       show write protect status
--wp-range                        set write protect range
--wp-enable                       enable write protection
--wp-disable                      disable write protection

Some examples of basic usage, these are all run on the device itself:

If you want to read the firmware from the SPI:
$ flashrom -p host -r image.bin

If you want to write a firmware image to the SPI:
$ flashrom -p host -w image.bin

If you want to read the ec image from the EC:
$ flashrom -p ec -r ec.bin

If you want to write an ec image to the EC:
$ flashrom -p ec -w ec.bin

If you just want to update your firmware and EC to the latest version in your Chrome OS system, ignoring any safety checks, run the below which invokes flashrom for you:
$ chromeos-firmwareupdate --mode=incompatible_update

Warning: when running flashrom on an x86 host, the Intel Management Engine (ME) firmware region will be read back as 0xff bytes, and writes to the ME region will be silently discarded.  This means that if you make a backup of your flash contents with flashrom -p host -r backup.bin and then try to restore backup.bin via servo, the ME region will be overwritten with 0xff bytes and your system will no longer boot.  The ME region can be identified by running dump_fmap on the firmware image; here is an example from Link:

area:            3
area_offset:     0x00001000
area_size:       0x001ff000 (2093056)
area_name:       SI_ME

The /usr/sbin/chromeos-firmwareupdate script contains a copy of the factory BIOS image (including the ME firmware), if you've already run into this problem.

Servo

Servo has an FT2232 USB <--> SPI interface which Flashrom can use to pass commands thru to the SPI chip. All you need to do is set the programmer target (-p ft2232_spi:type=servo-v2) and enable/disable the buffers on the flex cable using dut-control (from the hdctools package).

One thing to watch for is the voltage argument to dut-control. Most SPI chips operate at either 1.8V or 3.3V. This is set by spi2_vref:ppXXXX where XXXX is 1800 or 3300.

Example for programming a 1.8V SPI chip:
$ dut-control spi2_vref:pp1800 spi2_buf_en:on spi2_buf_on_flex_en:on spi_hold:off cold_reset:on
$ sudo /usr/sbin/flashrom -p ft2232_spi:type=servo-v2 -w <image to program>
$ dut-control spi2_vref:off spi2_buf_en:off spi2_buf_on_flex_en:off spi_hold:off cold_reset:off
To control hardware write-protect on DUT using Servo:

$ dut-control fw_wp_en:on fw_wp_vref:pp1800 # Enable WP override on Servo, this example assumes 1.8V chip

$ dut-control fw_wp:off # Force WP off

$ sudo /usr/sbin/flashrom -p ft2232_spi:type=servo-v2 --wp-disable # Disable software WP (--wp-enable and --wp-range could also be done here)

$ dut-control fw_wp_en:off fw_wp_vref:off # Disable WP override on Servo.

In this example we enable WP override, force the signal "off" (drive it high, even if /WP is asserted by screw/H1/etc), disable software WP, and then disable WP override. With software WP disabled we can write to the entire chip regardless of the hardware WP status.

More details about how to run it with Servo are available here and here (for Googlers only).


Partial Reads and Writes


Flashrom can be instructed to target only a specific region on the flash chip. This allows scripts (especially factory installer and autoupdate) to selectively update regions without spending a lot of time reading or updating the entire flash memory.


Selectively include regions

To include a region in a read/write operation, use the -i option:

-i | --image <name>[:<file>] only access image <name> from flash layout


The [:<file>] argument is optional and has an interesting effect on -r and -w. If a file is not supplied, flashrom will operate on a file that is the same size as the targeted flash chip. For example, if you wish to write sections FOO and BAR from a 4MB file to a 4MB flash chip, you could do: flashrom -p <programmer> -i FOO -i BAR -w filename.bin




If files are specified as arguments to -i options, flashrom will not require an argument to -w or -r and instead will work with the files supplied via -i arguments. So if you have separate files for FOO and BAR which are not part of a larger image, let's call them foo.bin and bar.bin, you can write them to the firmware ROM like so: flashrom -p <programmer> -i FOO:foo.bin BAR:bar.bin -w



One can also use a combination:

  • In the read case, supplying a filename as an argument to "-r" will produce a ROM-sized file in addition to files produced for "-i" arguments which specify a filename.
  • In the write case, filenames supplied as arguments to "-i" options take precedence. This allows the user to supply a ROM-sized file to "-w" but also patch its content using files supplied to "-i". for example, if you have a standard ROM image but you want to apply custom data to a specific region when flashing.

Layout

When -i is used, Flashrom will search for the flashmap (fmap) and compare region names with the name supplied by the user. If the user wishes to supply a custom mapping instead of using the flashmap, a layout file can be used:

-l | --layout                     read ROM layout from <file>


For example, this will write the custom-defined ranges from the supplied filename to the ROM:

echo "000000:0fffff FOO" > layout.txt

echo "200000:2fffff BAR" >> layout.txt

flashrom -p <programmer> -l layout.txt -i FOO -i BAR -w filename.bin


Selective verification of partial writes

By default, flashrom verifies the result of any destructive operation by reading and comparing the entire ROM. To only verify portions which have supposedly been written, --fast-verify can be used:

   --fast-verify                     only verify -i part


This is generally considered safe since a discrepancy in the partially written portions will indicate that something is likely wrong elsewhere.


TODO(dhendrix): That should probably be renamed "--partial-verify" or something.


Speeding Up Writes


This section describes some shortcuts that can be useful for developers. Do not rely on the behavior described below for production code. It's really only intended to help developers iterate faster.

Erase and write operations are orders of magnitude slower than reads on typical flash memory devices. Thus, flashrom figures out which blocks need to be updated so that it can try and skip as many as possible. The basic steps are:
  1. Read entire ROM to obtain a reference image before any destructive operation takes place.
  2. Go thru write algorithm and only erase/write blocks as needed.
  3. Read the ROM again to verify that it matches the supplied file.
The main way to speed things up is to skip the first and last verification steps.

Skipping verification
If you're confident that the bits will land where they need to, you can save time by skipping the verification step.
   -n | --noverify                   don't auto-verify

Supplying original ROM content with a file
This will allow you to skip the initial step of obtaining a reference image:
   --diff <file>                     diff from file instead of ROM

This tells flashrom that the file supplied as an argument to --diff will be used as a reference image, so it will skip reading the ROM content. This is useful if you can track exactly what is on the ROM, but can be lead to frustrating bugs if the contents get out of sync. Use with caution!

Example (note: this assumes that you have previously flashed "old.bin"):
flashrom -p ft2232_spi:type=servo-v2 -w new.bin --diff old.bin && cp new.bin old.bin

Power management pitfalls to watch out for


In short:
  • System must remain running (given).
  • powerd must not tickle the embedded controller (See "Embedded Controller Interactions" below).
  • Performance should not be significantly degraded.
Chrome OS devices usually read firmware at least once per boot-up often to obtain things contained in VPD (e.g. antennae calibration data), populate entries for chrome://system, and small system maintenance tasks.

Embedded Controller interactions

Embedded Controllers are independent microcontrollers which coexist in a platform to service some power management routines via ACPI or a other interface. This often includes handling lid switch events, sensors (such as ambient light sensor), thermal management, etc.

The way they are designed can make firmware updates difficult. To cut down on cost, often times they lack internal flash memory and have limited amount of SRAM so they need to access the firmware ROM to load new routines. To make matters more complicated some systems use the same firmware ROM for both the host (PCH, SoC, etc) and the EC.

In rare circumstances where we're updating the EC firmware itself, Flashrom will pause the EC. However, doing so has highly visible side-effects such as disabling keyboard, causing the fan to spin up all the way, or dimming the screen. For more frequent host firmware updates, which can take a long time, we have historically relied on stopping powerd and then restarting it after we're done. This avoids the problem of interrupting the EC such that it needs to load more code, and avoids UI jank that can last up to a minute and cause a user to try to reboot the system. For historical context, see chromium-os:18895.

Shared SPI block diagram

Non-shared SPI block diagram


Performance

We like firmware updates to be done as quickly as possible. This is important not only to minimize any side-effects the user might see as well as overall risk, but also to optimize time spent on the assembly line when a device is being manufactured (chromium-os:14139).

Some older systems had performance issues when flashrom ran if powerd was enabled. This was due to poor DVFS implementations that could dramatically affect the behavior of the kernel's scheduler and cause huge delays when running flashrom.

One side-effect was that flashrom would take an excessively long time to complete due to bad usleep() behavior (chromium-os:15025). However, when we disabled powerd we found that the UI would become janky (chromium-os:19321). Eventually settled on disabling powerd only for operations expected to take a long time and are destructive (erase/writes).

Now that powerd is smarter, we stopped disabling powerd (chromium:400641) and expect it to avoid doing anything which may degrade performance while flashrom is running.

Testing

Recent (ca. 2016) improvements have been made to testing capabilities. A new set of test scripts has been merged and flashrom is gaining some built-in testing capabilities.

Built-in Test
Built-in tests are currently limited to write-protect testing using the "--wp-test" option. Flashrom will read the write-protect status and attempt to overwrite the protected region using all the available sector, block, and chip erase commands.

Test Script v2
The test script is used primarily for regression testing. It accepts two flashrom binaries as inputs, one which is presumed to be stable ("old") and one which is to be tested ("new").

The test can be performed on a local host or a remote host with SSH access. Additionally, an external programmer (such as Servo, Dediprog, etc) can be used as part of the test setup.

Documentation for test script v2: https://goo.gl/3jNoL7

Flashrom Test Script v2 ‎‎(master doc)‎‎




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