Failure is in:

https://luci-milo.appspot.com/buildbot/chromeos/coral-paladin/1102

=== Start output for job chromeos-firmware-coral-0.0.1-r25 (0m0.1s) ===
chromeos-firmware-coral-0.0.1-r25: >>> Fetching (1 of 1) chromeos-base/chromeos-firmware-coral-0.0.1-r25::coral-private for /build/coral/
chromeos-firmware-coral-0.0.1-r25: !!! Fetched file: Coral.9916.0.0.tbz2 VERIFY FAILED!
chromeos-firmware-coral-0.0.1-r25: !!! Reason: Insufficient data for checksum verification
chromeos-firmware-coral-0.0.1-r25: !!! Got:      
chromeos-firmware-coral-0.0.1-r25: !!! Expected: MD5 RMD160 SHA1 SHA256 SHA512 WHIRLPOOL
chromeos-firmware-coral-0.0.1-r25: !!! Fetched file: Coral_EC.9916.0.0.tbz2 VERIFY FAILED!
chromeos-firmware-coral-0.0.1-r25: !!! Reason: Insufficient data for checksum verification
chromeos-firmware-coral-0.0.1-r25: !!! Got:      
chromeos-firmware-coral-0.0.1-r25: !!! Expected: MD5 RMD160 SHA1 SHA256 SHA512 WHIRLPOOL
chromeos-firmware-coral-0.0.1-r25:  * Fetch failed for 'chromeos-base/chromeos-firmware-coral-0.0.1-r25'
chromeos-firmware-coral-0.0.1-r25: >>> Failed to emerge chromeos-base/chromeos-firmware-coral-0.0.1-r25 for /build/coral/
=== Complete: job chromeos-firmware-coral-0.0.1-r25 (0m0.1s) ===

13:28:48: INFO: Attempting to cherry-pick change chromeos/overlays/overlay-coral-private:refs/changes/92/452992/4:*34c8a6e5 "coral: uprev FW to 9933.0.0"
Trying simple merge.
[patch_branch 65ae9b4] coral: uprev FW to 9933.0.0
 Author: Tim Chen <Tim-Chen@quantatw.com>
 Date: Tue Sep 12 17:54:05 2017 +0800
 2 files changed, 4 insertions(+), 4 deletions(-)
 rewrite chromeos-base/chromeos-firmware-coral/Manifest (100%)

...

[ebuild  rR    ] chromeos-base/chromeos-firmware-coral-0.0.1-r25::coral-private to /build/coral/ USE="bootimage cros_ec unibuild -cros_host -profiling" 0 KiB

...

Fetched chromeos-base/chromeos-config-bsp-0.0.1-r867 in 0.49s
Started chromeos-base/chromeos-config-bsp-0.0.1-r867 (logged in /tmp/chromeos-config-bsp-0.0.1-r867-Gikesf)

...

Fetched chromeos-base/chromeos-firmware-coral-0.0.1-r25 in 0.13s
=== Start output for job chromeos-firmware-coral-0.0.1-r25 (0m0.1s) ===
chromeos-firmware-coral-0.0.1-r25: >>> Fetching (1 of 1) chromeos-base/chromeos-firmware-coral-0.0.1-r25::coral-private for /build/coral/
chromeos-firmware-coral-0.0.1-r25: !!! Fetched file: Coral.9916.0.0.tbz2 VERIFY FAILED!
chromeos-firmware-coral-0.0.1-r25: !!! Reason: Insufficient data for checksum verification
chromeos-firmware-coral-0.0.1-r25: !!! Got:      
chromeos-firmware-coral-0.0.1-r25: !!! Expected: MD5 RMD160 SHA1 SHA256 SHA512 WHIRLPOOL
chromeos-firmware-coral-0.0.1-r25: !!! Fetched file: Coral_EC.9916.0.0.tbz2 VERIFY FAILED!
chromeos-firmware-coral-0.0.1-r25: !!! Reason: Insufficient data for checksum verification
chromeos-firmware-coral-0.0.1-r25: !!! Got:      
chromeos-firmware-coral-0.0.1-r25: !!! Expected: MD5 RMD160 SHA1 SHA256 SHA512 WHIRLPOOL
chromeos-firmware-coral-0.0.1-r25:  * Fetch failed for 'chromeos-base/chromeos-firmware-coral-0.0.1-r25'
chromeos-firmware-coral-0.0.1-r25: >>> Failed to emerge chromeos-base/chromeos-firmware-coral-0.0.1-r25 for /build/coral/
=== Complete: job chromeos-firmware-coral-0.0.1-r25 (0m0.1s) ===

...

Completed chromeos-base/chromeos-config-bsp-0.0.1-r867 (in 0m10.6s)

Started chromeos-base/chromeos-config-0.0.1-r2 (logged in /tmp/chromeos-config-0.0.1-r2-mYAx2U)
...
Completed chromeos-base/chromeos-config-0.0.1-r2 (in 0m6.9s)

the firmware package is missing an uprev.  portage is WAI here.

We have always done this previously. But is it possible to avoid the need for that?

Since chromeos-firmware-coral depends on chromeos-config and thus chromeos-config-bsp, which has a file changed within its purview:

CROS_WORKON_SUBDIRS_TO_REV=( chromeos-base/chromeos-config-bsp/files )

could this not cause chromeos-config-bsp to uprev, and thus chromeos-firmware to do the same?

I ran coral-paladin and coral-release trybots with these two CLs:

https://chrome-internal-review.googlesource.com/c/chromeos/overlays/overlay-coral-private/+/452992
https://chromium-review.googlesource.com/c/chromiumos/chromite/+/664484

Both succeeded:

https://uberchromegw.corp.google.com/i/chromiumos.tryserver/builders/paladin/builds/3752
https://uberchromegw.corp.google.com/i/chromiumos.tryserver/builders/release/builds/14784

Then just to be sure I ran them again with just the uprev CL:

https://uberchromegw.corp.google.com/i/chromiumos.tryserver/builders/paladin/builds/3753
https://uberchromegw.corp.google.com/i/chromiumos.tryserver/builders/release/builds/14797

Unfortunately both of these succeeded too. I did not expect that.

Both results show a successful update from 9916 to 9933. I wonder if the files and SRC_URI are cached by the builders?

I'm trying two more trybots, this time without the uprev.

I'm going to claim this is blocked on  crbug.com/764075  since it does indeed seem that the functionality we need was removed.

The CL is merged. I am not sure whether the next release build will pick up the new version or not.