quirks/dmi: warn once when /scheme/acpi/dmi is absent (Gap 17)

The Phase R10 audit found that dmi::read_dmi_info() returns Err(())
silently when acpid is not yet serving the DMI endpoint (the deep
Blocker 2 work that wires acpid SMBIOS Type 0/1/2 parsing into a
kernel-exposed scheme). Without an explicit log, every DMI lookup
in every driver fails opaquely, masking the root cause for anyone
triaging missing quirk rules.

The log is rate-limited to a single warn! per process lifetime via
a static AtomicBool, so the boot log is not flooded even when many
drivers call read_dmi_info() during enumeration. The 120/120 unit
tests in redox-driver-sys continue to pass.

local/recipes/drivers/redox-driver-sys/source/src/quirks/dmi.rs

@@ -171,13 +171,28 @@ pub struct DmiXhciQuirkRule {
 
 /// Read DMI/SMBIOS data from the ACPI scheme.
 ///
-/// Returns `Err(())` if DMI data is not available (e.g., early boot,
-/// no SMBIOS table, or acpid not running).
+/// Returns `Err(())` if DMI data is not available. Phase R10 audit
+/// (2026-06-07) — emits a single `log::warn!` per process on the first
+/// failure, so the absence of `/scheme/acpi/dmi` is visible in the
+/// boot log instead of silently producing empty DMI matches on every
+/// lookup.
 pub fn read_dmi_info() -> Result<DmiInfo, ()> {
+    use std::sync::atomic::{AtomicBool, Ordering};
+    static WARNED: AtomicBool = AtomicBool::new(false);
+
     let dmi_path = "/scheme/acpi/dmi";
     match std::fs::read_to_string(dmi_path) {
         Ok(data) => parse_dmi_data(&data),
-        Err(_) => Err(()),
+        Err(e) => {
+            if !WARNED.swap(true, Ordering::Relaxed) {
+                log::warn!(
+                    "quirks: cannot read DMI from {dmi_path}: {e}; \
+                     acpid DMI producer is not serving data, \
+                     all DMI-based rules are inert"
+                );
+            }
+            Err(())
+        }
     }
 }