FYI: bcm53xx brcmfmac init issue on RT-AC5300 (PR #21654)

[Tom Brautaset]

Hi all,

I would like to share a short FYI regarding a bcm53xx / brcmfmac
behavior observed on ASUS RT-AC3200 and RT-AC5300, and to point to a
focused PR addressing it.

PR: https://github.com/openwrt/openwrt/pull/21654

Summary of findings

RT-AC3200
When flashed and tested correctly, RT-AC3200 does not require any additional
baseline NVRAM values for Wi-Fi to function. A complete, vendor-provided
ASUSWRT NVRAM works as-is.

RT-AC5300
When flashing directly from ASUSWRT to OpenWrt while preserving a complete
vendor NVRAM, radio0 fails to appear.
Further investigation shows that brcmfmac fails during early attach while
parsing a large set (700+) of vendor-generated wl*_ runtime variables.
Removing this runtime state allows Wi-Fi to initialize reliably.

The intent of the PR is not to replace vendor calibration data or expand the
default NVRAM baseline, but to remove only vendor-generated runtime state that
is incompatible with brcmfmac during early initialization.

________________________________

Alternative flashing workflows (advanced users)

In addition to the documented CFE recovery method, the following SSH-based
workflows have been tested successfully. These are intended for experienced
users and do not replace the recommended recovery procedure.

Users are expected to download the appropriate firmware images themselves from
the official OpenWrt and ASUS sources.

Flashing OpenWrt directly from ASUSWRT:

ssh admin at 192.168.1.1

cd /tmp && \
  curl -L -o fw.trx "<OPENWRT_TRX_URL>" && \
  mtd-write2 fw.trx linux && \
  reboot

Where <OPENWRT_TRX_URL> refers to the official OpenWrt firmware image for the
device, downloaded from openwrt.org.

Flashing back to ASUSWRT from OpenWrt:

ssh root at 192.168.1.1

URL="<ASUSWRT_TRX_URL>" && \
  uclient-fetch -O /tmp/fw.trx "$URL" && \
  sha256sum /tmp/fw.trx && \
  mtd erase nvram && \
  sysupgrade -n /tmp/fw.trx

Where <ASUSWRT_TRX_URL> refers to the official ASUS firmware image for the
device, downloaded from ASUS support pages.

________________________________

Notes

Sysupgrade configuration preservation and LuCI backup archive format are
separate topics and will be handled independently.

This mail is intended purely as documentation and a pointer to the PR above.

Thanks for reading.

Best regards,
Tom