[tip: x86/core] x86/smpboot: Remove confusing quirk usage in INIT delay

[tip-bot2 for Sohil Mehta]

The following commit has been merged into the x86/core branch of tip:

Commit-ID:     58d1c1fd0319d00e83f58f2a195847e189e447ce
Gitweb:        https://git.kernel.org/tip/58d1c1fd0319d00e83f58f2a195847e189e447ce
Author:        Sohil Mehta <sohil.mehta@xxxxxxxxx>
AuthorDate:    Wed, 19 Feb 2025 18:41:27 
Committer:     Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Wed, 19 Mar 2025 11:19:48 +01:00

x86/smpboot: Remove confusing quirk usage in INIT delay

Very old multiprocessor systems required a 10 msec delay between
asserting and de-asserting INIT but modern processors do not require
this delay.

Over time the usage of the "quirk" wording while setting the INIT delay
has become misleading. The code comments suggest that modern processors
need to be quirked, which clears the default init_udelay of 10 msec,
while legacy processors don't need the quirk and continue to use the
default init_udelay.

With a lot more modern processors, the wording should be inverted if at
all needed. Instead, simplify the comments and the code by getting rid
of "quirk" usage altogether and clarifying the following:

  - Old legacy processors -> Set the "legacy" 10 msec delay
  - Modern processors     -> Do not set any delay

No functional change.

Signed-off-by: Sohil Mehta <sohil.mehta@xxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20250219184133.816753-10-sohil.mehta@xxxxxxxxx
---
 arch/x86/kernel/smpboot.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 42ca131..5e586f5 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -635,10 +635,9 @@ static void impress_friends(void)
  * But that slows boot and resume on modern processors, which include
  * many cores and don't require that delay.
  *
- * Cmdline "init_cpu_udelay=" is available to over-ride this delay.
- * Modern processor families are quirked to remove the delay entirely.
+ * Cmdline "cpu_init_udelay=" is available to override this delay.
  */
-#define UDELAY_10MS_DEFAULT 10000
+#define UDELAY_10MS_LEGACY 10000
 
 static unsigned int init_udelay = UINT_MAX;
 
@@ -650,7 +649,7 @@ static int __init cpu_init_udelay(char *str)
 }
 early_param("cpu_init_udelay", cpu_init_udelay);
 
-static void __init smp_quirk_init_udelay(void)
+static void __init smp_set_init_udelay(void)
 {
 	/* if cmdline changed it from default, leave it alone */
 	if (init_udelay != UINT_MAX)
@@ -664,7 +663,7 @@ static void __init smp_quirk_init_udelay(void)
 		return;
 	}
 	/* else, use legacy delay */
-	init_udelay = UDELAY_10MS_DEFAULT;
+	init_udelay = UDELAY_10MS_LEGACY;
 }
 
 /*
@@ -1075,7 +1074,7 @@ void __init native_smp_prepare_cpus(unsigned int max_cpus)
 
 	uv_system_init();
 
-	smp_quirk_init_udelay();
+	smp_set_init_udelay();
 
 	speculative_store_bypass_ht_init();