diff --git a/docs/firmware.md b/docs/firmware.md
index 82bf20b..e779ce1 100644
--- a/docs/firmware.md
+++ b/docs/firmware.md
@@ -45,6 +45,52 @@ until you supply it you get an unaccelerated display.
 Each file is independent, so a partial recovery is still worth having —
 `qcdxkmsuc850.mbn` on its own buys you working graphics.
 
+### Confirmed on the hardware
+
+This is not inferred from the device tree. On a machine with the generic
+Adreno firmware present and the model-signed blob absent, the GPU gets two
+files in and then stops:
+
+```
+[drm:adreno_request_fw]   loaded qcom/a630_sqe.fw from new location
+[drm:adreno_request_fw]   loaded qcom/a630_gmu.bin from new location
+[drm:zap_shader_load_mdt] *ERROR* Unable to load qcom/sdm850/LENOVO/81JL/qcdxkmsuc850.mbn
+[drm:adreno_load_gpu]     *ERROR* gpu hw init failed: -2
+```
+
+So the generic pieces are necessary and not sufficient, and the zap shader is a
+hard requirement rather than an optimisation. Two details follow from that
+trace:
+
+The driver never falls back to `sdm845/a630_zap.mbn`, even though the file is
+installed — the device tree's `firmware-name` pins the model-specific path. Nor
+would falling back help: the zap shader is signed against the device's own
+secure-boot chain, and the Snapdragon 845 development board's copy will not
+validate here.
+
+The display keeps working throughout. `msm_dpu` binds the panel and the console
+lands on `msmdrmfb` regardless, so a failed GPU costs you acceleration, not a
+picture. A desktop still runs on llvmpipe — though `/dev/dri/renderD128` is
+present even when `hw init` has failed, so mesa may try freedreno, fail, and
+take the display manager down with it. `LIBGL_ALWAYS_SOFTWARE=1` in
+`/etc/environment` avoids that.
+
+### These have to be in the initramfs
+
+`msm_dpu` probes about six seconds in, while the initramfs is still the root
+filesystem, and does not retry. Firmware that only exists on the real root is
+therefore invisible to it:
+
+```
+msm_dpu ae01000.display-controller: Direct firmware load for qcom/a630_sqe.fw failed with error -2
+```
+
+`overlay/etc/dracut.conf.d/10-c630.conf` puts the Adreno files in the initramfs
+for this reason, and `c630-firmware` adds the extracted DSP blobs to it after
+extraction — the ADSP has to be up before the root filesystem is mounted, and
+dracut rejects `install_items` globs that match nothing, so the entry can only
+be written once the files exist.
+
 ## Finding them on a backup
 
 If Windows is long gone from the machine but you kept a copy of the files, one