devd: Improve devmatch support

We know that calling devmatch will be futile if there's no plug and play
information for it to match on. Avoid this generically when we see
	"? at +on"
which happens only when the location and pnpinfo aren't provided. Don't
call "service devmatch quietstart" here.

We also ignore ACPI devices with a _HID of none. These also will never
load a new driver, so avoid calling "service devmatch quietstart" here too.

Use the more compatct "$*" instead of "'?'$_" when calling "service
devmatch quietstart" since it will evaluate to the same thing.

On my laptop, this eliminates 45% of the calls to devmatch. While it
would be even better to integrate devmatch into devd (so we only parse
linker.hints once), that will have to wait for another day as it's a bit
more complex to arrange that avoiding easy to avoid calls.

Sponsored by:		Netflix
Reviewed by:		emaste
Differential Revision:	https://reviews.freebsd.org/D42326

1 files changed, 22 insertions, 4 deletions

diff --git a/sbin/devd/devmatch.conf b/sbin/devd/devmatch.conf
index 085338eabca4..a7c27857c0bd 100644
--- a/sbin/devd/devmatch.conf
+++ b/sbin/devd/devmatch.conf
@@ -1,14 +1,32 @@
+# Implement the run-time component of devmatch by reacting to nomatch events.
+
 #
+# Ignore those devices that can't possibly match. When there's neither a
+# location, nor a pnpinfo string, we know that there's nothing devmatch can
+# match on. When it's only a location, it'd debateable, but for nomatch
+# events, we can't disambiguate between the two reliably.
 #
+nomatch 101 {
+	match "_" " +at +on .*";
+};
 
 #
-# Example devd configuration file for automatically
-# loading what modules we can based on nomatch
-# events.
+# Ignore ACPI devices whose _HID is none. These cannot tell us what to load,
+# since 'none' is not a valid id. There's no need to call devvmatch for these either.
+#
+nomatch 101 {
+	match "_HID" "none";
+	match "bus" "acpi[0-9]+";
+};
+
 #
 # Generic NOMATCH event
+#
+# Note: It would be better to have some internal-to-devd action that will do
+# what devmatch does without re-parsing loader.hints for each invocation
+#
 nomatch 100 {
-	action "service devmatch quietstart '?'$_";
+	action "service devmatch quietstart $*";
 };
 
 # Add the following to devd.conf to prevent this from running: