arm64: capabilities: Handle shared entries

Some capabilities have different criteria for detection and associated
actions based on the matching criteria, even though they all share the
same capability bit. So far we have used multiple entries with the same
capability bit to handle this. This is prone to errors, as the
cpu_enable is invoked for each entry, irrespective of whether the
detection rule applies to the CPU or not. And also this complicates
other helpers, e.g, __this_cpu_has_cap.

This patch adds a wrapper entry to cover all the possible variations
of a capability by maintaining list of matches + cpu_enable callbacks.
To avoid complicating the prototypes for the "matches()", we use
arm64_cpu_capabilities maintain the list and we ignore all the other
fields except the matches & cpu_enable.

This ensures :

 1) The capabilitiy is set when at least one of the entry detects
 2) Action is only taken for the entries that "matches".

This avoids explicit checks in the cpu_enable() take some action.
The only constraint here is that, all the entries should have the
same "type" (i.e, scope and conflict rules).

If a cpu_enable() method is associated with multiple matches for a
single capability, care should be taken that either the match criteria
are mutually exclusive, or that the method is robust against being
called multiple times.

This also reverts the changes introduced by commit 67948af41f2e6818ed
("arm64: capabilities: Handle duplicate entries for a capability").

Cc: Robin Murphy <robin.murphy@arm.com>
Reviewed-by: Dave Martin <dave.martin@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

1 files changed, 12 insertions, 0 deletions

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index a16eb0731290..09b0f2a80c8f 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -323,6 +323,18 @@ struct arm64_cpu_capabilities {
 			bool sign;
 			unsigned long hwcap;
 		};
+		/*
+		 * A list of "matches/cpu_enable" pair for the same
+		 * "capability" of the same "type" as described by the parent.
+		 * Only matches(), cpu_enable() and fields relevant to these
+		 * methods are significant in the list. The cpu_enable is
+		 * invoked only if the corresponding entry "matches()".
+		 * However, if a cpu_enable() method is associated
+		 * with multiple matches(), care should be taken that either
+		 * the match criteria are mutually exclusive, or that the
+		 * method is robust against being called multiple times.
+		 */
+		const struct arm64_cpu_capabilities *match_list;
 	};
 };