Stop the modem crash loop, and record what it is not

Fedora runs rmtfs with -r, which starts the modem remoteproc at boot. Since
the modem never gets past RF init, every C630 sits in a fatal crash and
recovery cycle every ~3.4 seconds from boot onwards — and is already a dozen
crashes deep by the time anyone logs in, which quietly confuses any manual
experiment. Drop the -r so the modem stays offline until asked for.

Also record today's eliminations, each of which closes an avenue: both
published _nm firmware builds are rejected by the boot ROM, not just the
newest; the PEP tables in this machine's own ACPI show Windows gives the
modem seven clocks, one 752 mV rail vote, cx/mx and IPA bandwidth, and
nothing whatsoever for RF — so the host does not power the RF front end on
either OS, and the one clock mainline lacks changes nothing when forced on;
and kernel bracketing is stuck, because 5.10 will not boot here at all.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011XgGF5wfxLDAybVnNz6eNQ

docs/drafts/linux-arm-msm-report.md

@@ -38,12 +38,27 @@ here is what I have eliminated:
   for this machine containing five distinct mba/mpss builds (including
   a 2018-vintage pair matching this unit's manufacture date and 2019
   UEFI, 9UCN33WW(V2.06)); the aarch64-laptops copies differ again by
-  checksum. All produce the identical fatal. The _nm ("no modem")
-  variants are rejected earlier (PBL "unexpected status" / MPSS header
-  authentication failed -3), as expected for the wrong SKU.
+  checksum. All produce the identical fatal.
 
 - Kernel version, at least recently. Fedora 7.1.5 and Fedora 6.12.15
-  crash identically, same DTB.
+  crash identically, same DTB. (I could not get anything older to
+  boot here to widen the bracket: a 5.10.261 build with the SDM845
+  platform, UFS, PHY and ext4 support all enabled dies after the EFI
+  stub with no console output, with earlycon=efifb and
+  arm-smmu.disable_bypass=0 both tried. Suggestions welcome.)
+
+- Host-side power. I decoded the PEP tables in this machine's ACPI
+  for \_SB.AMSS: Windows gives the modem seven clocks (the six in
+  mainline's mss_pil node plus gcc_mss_axis2_clk), one regulator vote
+  (SMPS2_C at 752 mV), rail_cx/rail_mx at level 384, and IPA bus
+  bandwidth. No GPIOs, no footswitches, and no votes on the CXO RFCLK
+  buffers, so the host does not power the RF front end on Windows
+  either. Holding gcc_mss_axis2_clk enabled from a test module before
+  starting the modem changes nothing.
+
+- The _nm ("no modem") firmware, in both published builds. The boot
+  ROM rejects either _nm MBA with "PBL returned unexpected status
+  -284557301"; with the full MBA the _nm mpss fails authentication.
 
 - Userspace. rmtfs and tqftpserv running (in-kernel qrtr-ns and
   pd-mapper); wlanmdsp.mbn reachable through tqftpserv's firmware