Re: [PATCH v2] powerpc/powernv: Cache OPAL check_token() results
From: Nikhil Kumar Singh <hidden>
Date: 2026-07-07 07:07:12
On 26/06/26 18:05, Shivang Upadhyay wrote:
quoted hunk ↗ jump to hunk
diff --git a/arch/powerpc/platforms/powernv/opal.c b/arch/powerpc/platforms/powernv/opal.c index 1946dbdc9fa1..1e9cb5271ee7 100644 --- a/arch/powerpc/platforms/powernv/opal.c +++ b/arch/powerpc/platforms/powernv/opal.c@@ -1125,6 +1125,36 @@ EXPORT_SYMBOL_GPL(opal_flash_read); EXPORT_SYMBOL_GPL(opal_flash_write); EXPORT_SYMBOL_GPL(opal_flash_erase); EXPORT_SYMBOL_GPL(opal_prd_msg); + +/** + * opal_check_token - Check if an OPAL call token is supported + * @token: OPAL token number to check + * + * Returns 1 if supported, 0 if not. + */ +int64_t opal_check_token(uint64_t token) +{ + static u8 token_cache[OPAL_LAST]; + enum { + SUPP_UNKNOWN = 0, + PRESENT, + ABSENT + }; + + if (token > OPAL_LAST) + return 0; + + if (token_cache[token] == SUPP_UNKNOWN) {
Hi Shivang, Thanks for the v2 patch. This is a great optimization and definitely helps reduce unnecessary overhead. I have one small suggestion. You can wrap the if (token_cache[token] == SUPP_UNKNOWN) check, as well as the if (token > OPAL_LAST) check above it, with unlikely(), since this function is in the hot path. Out-of-bounds tokens are very rare, and after the cache is populated, the SUPP_UNKNOWN condition is expected to be false in almost all cases. Wrapping these checks with unlikely() will help the compiler optimize branch prediction. Thanks, ~ Nikhil
+ /* Do the actual opal_call here */
+ if (opal_check_token_call(token)) {
+ token_cache[token] = PRESENT;
+ } else {
+ token_cache[token] = ABSENT;
+ }
+ }
+
+ return (token_cache[token] == PRESENT);
+}
EXPORT_SYMBOL_GPL(opal_check_token);
/* Convert a region of vmalloc memory to an opal sg list */