docs/fingerprint: Update chromeos-config and flashing instructions

BRANCH=none
BUG=none
TEST=view in gitiles

Change-Id: Ibc97efb7a1746cb6cbb5422104d72be8b708681e
Signed-off-by: Tom Hughes <tomhughes@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2015141
Commit-Queue: Craig Hesling <hesling@chromium.org>
Reviewed-by: Craig Hesling <hesling@chromium.org>

2 files changed, 32 insertions, 9 deletions

diff --git a/docs/fingerprint/fingerprint-factory-requirements.md b/docs/fingerprint/fingerprint-factory-requirements.md
index dfd66d8eb1..9849cdd393 100644
--- a/docs/fingerprint/fingerprint-factory-requirements.md
+++ b/docs/fingerprint/fingerprint-factory-requirements.md
@@ -7,8 +7,8 @@ fingerprint sensor.
 
 ## Contact
 
-For questions regarding this document, please contact the [Chrome OS
-Fingerprint Team].
+For questions regarding this document, please contact the
+[Chrome OS Fingerprint Team].
 
 ## Terminology
 
@@ -44,13 +44,20 @@ directory since multiple sensors may be used across a single "board" (e.g., the
 `hatch` board can use either `bloonchipper` or `dartmonkey`).
 
 The correct firmware type to use for a given board can be discovered with the
-following command:
+[Chrome OS Config] tool:
 
 ```bash
 (dut) $ cros_config /fingerprint board
 dartmonkey
 ```
 
+OR
+
+```bash
+(chroot) $  cros_config_host -c /build/<BOARD>/usr/share/chromeos-config/yaml/config.yaml -m <MODEL> get /fingerprint board
+dartmonkey
+```
+
 The corresponding firmware for the above command would be
 `/opt/google/biod/fw/dartmonkey_*.bin`.
 
@@ -64,7 +71,8 @@ When the FPMCU is completely blank a low-level flashing tool must be used to
 program an initial version of the FPMCU firmware. It’s possible to use the
 [`flash_fp_mcu`] script as this low-level flashing tool, though since it
 requires the AP and is not necessarily robust against failures, it is not
-recommended for mass-production.
+recommended for mass-production. More details about [`flash_fp_mcu`] are in the
+[Fingerprint flashing documentation].
 
 The initial version of the FPMCU firmware should be flashed either by the module
 house or by the factory. Once an initial version of the FPMCU firmware has been
@@ -89,7 +97,7 @@ device).
 `timberslide` is the daemon that periodically sends commands to the FPMCU to
 read the latest FPMCU logs. It writes the results to `/var/log/cros_fp.log`. It
 should be fine to leave running during tests, though it should be stopped before
-running the `flash_fp_mcu` script, since that script erases the entire FPMCU:
+running the [`flash_fp_mcu`] script, since that script erases the entire FPMCU:
 
 ```bash
 (dut) $ stop timberslide LOG_PATH=/sys/kernel/debug/cros_fp/console_log
@@ -467,3 +475,5 @@ Wrote /tmp/fp.1.png (14025 bytes)
 [Chrome OS Fingerprint Team]: http://go/cros-fingerprint-docs
 [Factory Fingerprint Sensor Testing for `nocturne`]: http://go/fingerprint-factory-testing-nocturne
 [`flash_fp_mcu`]: https://chromium.googlesource.com/chromiumos/platform/ec/+/master/util/flash_fp_mcu
+[Fingerprint flashing documentation]: ./fingerprint.md#factory-rma-dev-updates
+[Chrome OS Config]: https://chromium.googlesource.com/chromiumos/platform2/+/master/chromeos-config/README.md
diff --git a/docs/fingerprint/fingerprint.md b/docs/fingerprint/fingerprint.md
index 21ce372755..2c11992a7a 100644
--- a/docs/fingerprint/fingerprint.md
+++ b/docs/fingerprint/fingerprint.md
@@ -31,13 +31,20 @@ building the EC code) are for fingerprint:
     *   Support for the STM32F412 for the FPMCU is not yet fully complete,
         but it is functional enough for testing.
 
-If you have access to a shell on your Chromebook, you can run the following
-command to determine the FPMCU that it contains:
+If you have access to a shell on your Chromebook, you can use [Chrome OS Config]
+to determine the FPMCU that it contains:
 
 ```bash
 (dut) $ cros_config /fingerprint board
 ```
 
+Alternatively, if you have a Chromium OS build, you can use [Chrome OS Config]
+in the chroot to determine the FPMCU:
+
+```bash
+(chroot) $  cros_config_host -c /build/<BOARD>/usr/share/chromeos-config/yaml/config.yaml -m <MODEL> get /fingerprint board
+```
+
 ## Building FPMCU Firmware Locally
 
 ### See `Makefile` target options
@@ -168,7 +175,7 @@ that do not have write protect enabled (dogfood devices, EVT, etc.)
 In production, only the RW portion of the firmware can be updated (unless the
 user disables [hardware write protection]).
 
-## Factory / RMA / Development Updates
+## Factory / RMA / Development Updates {#factory-rma-dev-updates}
 
 ### `flash_fp_mcu`
 
@@ -185,10 +192,14 @@ flash (both RO and RW). The FPMCU can only be put into bootloader mode when
 [hardware write protection] is disabled, which means [`flash_fp_mcu`] can only
 be used when [hardware write protection] is disabled.
 
+[`flash_fp_mcu`] is available in the [Chromium OS test image].
+
 ### `stm32mon`
 
 [`stm32mon`] is a tool used to send commands to the STM32 bootloader. We use it
-for development (through `flash_fp_mcu`) to erase and flash the entire chip.
+for development (through [`flash_fp_mcu`]) to erase and flash the entire chip.
+
+[`stm32mon`] is available in the [Chromium OS test image].
 
 ## Keys
 
@@ -316,3 +327,5 @@ This would make it a lot easier during both development and testing.
 [`timberslide`]: https://chromium.googlesource.com/chromiumos/platform2/+/master/timberslide
 [cros_ec_debugfs]: https://chromium.googlesource.com/chromiumos/third_party/kernel/+/9db44685934a2e4bc9180ea2de87a6c429672395/drivers/platform/chrome/cros_ec_debugfs.c
 [Fingerprint Factory Requirements]: ./fingerprint-factory-requirements.md
+[Chromium OS test image]: https://chromium.googlesource.com/chromiumos/platform/factory/+/master/README.md#building-test-image
+[Chrome OS Config]: https://chromium.googlesource.com/chromiumos/platform2/+/master/chromeos-config/README.md