linux-kernel - [PATCH] x86/apic: remove read/write test in verify_local

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Date:	Wed, 18 Mar 2015 16:45:54 -0400
From:	Bandan Das <bsd@...hat.com>
To:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>
Cc:	x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] x86/apic: remove read/write test in verify_local_apic()


Most newer processors have the APIC_ID read-only and this
test probably fails on most boxes anyway. Fix typos.

Signed-off-by: Bandan Das <bsd@...hat.com>
---
Honestly, I don't think this function is really needed.
It's called for both UP/MP but the return value isn't
used by any of them. Maybe, we should just remove it ?

 arch/x86/kernel/apic/apic.c | 18 +++++++-----------
 1 file changed, 7 insertions(+), 11 deletions(-)

diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index ad3639a..d54601e 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -1105,13 +1105,13 @@ int __init verify_local_APIC(void)
 	/*
 	 * The two version reads above should print the same
 	 * numbers.  If the second one is different, then we
-	 * poke at a non-APIC.
+	 * are poking at a non-APIC region.
 	 */
 	if (reg1 != reg0)
 		return 0;
 
 	/*
-	 * Check if the version looks reasonably.
+	 * Check if the version looks reasonable.
 	 */
 	reg1 = GET_APIC_VERSION(reg0);
 	if (reg1 == 0x00 || reg1 == 0xff)
@@ -1121,21 +1121,17 @@ int __init verify_local_APIC(void)
 		return 0;
 
 	/*
-	 * The ID register is read/write in a real APIC.
+	 * Just print the APIC ID
+	 * Writing to it is not a reliable test - older processors
+	 * support it, while newer processors don't
 	 */
 	reg0 = apic_read(APIC_ID);
-	apic_printk(APIC_DEBUG, "Getting ID: %x\n", reg0);
-	apic_write(APIC_ID, reg0 ^ apic->apic_id_mask);
-	reg1 = apic_read(APIC_ID);
-	apic_printk(APIC_DEBUG, "Getting ID: %x\n", reg1);
-	apic_write(APIC_ID, reg0);
-	if (reg1 != (reg0 ^ apic->apic_id_mask))
-		return 0;
+	apic_printk(APIC_DEBUG, "Getting Local APIC ID: %x\n", reg0);
 
 	/*
 	 * The next two are just to see if we have sane values.
 	 * They're only really relevant if we're in Virtual Wire
-	 * compatibility mode, but most boxes are anymore.
+	 * compatibility mode, but most boxes aren't anymore.
 	 */
 	reg0 = apic_read(APIC_LVT0);
 	apic_printk(APIC_DEBUG, "Getting LVT0: %x\n", reg0);
-- 
2.1.0

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