dmi: add support for exact DMI matches in addition to substring matching

dmi_match() considers a substring match to be a successful match.  This is
not always sufficient to distinguish between DMI data for different
systems.  Add support for exact string matching using strcmp() in addition
to the substring matching using strstr().

The specific use case in the i915 driver is to allow us to use an exact
match for D510MO, without also incorrectly matching D510MOV:

  {
	.ident = "Intel D510MO",
	.matches = {
		DMI_MATCH(DMI_BOARD_VENDOR, "Intel"),
		DMI_EXACT_MATCH(DMI_BOARD_NAME, "D510MO"),
	},
  }

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Cc: <annndddrr@gmail.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Cornel Panceac <cpanceac@gmail.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Greg KH <greg@kroah.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 9 insertions, 3 deletions

diff --git a/drivers/firmware/dmi_scan.c b/drivers/firmware/dmi_scan.c
index b95159b33c39..eb760a218da4 100644
--- a/drivers/firmware/dmi_scan.c
+++ b/drivers/firmware/dmi_scan.c
@@ -551,9 +551,15 @@ static bool dmi_matches(const struct dmi_system_id *dmi)
 		int s = dmi->matches[i].slot;
 		if (s == DMI_NONE)
 			break;
-		if (dmi_ident[s]
-		    && strstr(dmi_ident[s], dmi->matches[i].substr))
-			continue;
+		if (dmi_ident[s]) {
+			if (!dmi->matches[i].exact_match &&
+			    strstr(dmi_ident[s], dmi->matches[i].substr))
+				continue;
+			else if (dmi->matches[i].exact_match &&
+				 !strcmp(dmi_ident[s], dmi->matches[i].substr))
+				continue;
+		}
+
 		/* No match */
 		return false;
 	}