[patch V3 33/60] x86/apic/ipi: Tidy up the code and fixup comments

[Thomas Gleixner]

Replace the undecodable comment on top of the function, replace the space
consuming zero content comments with useful ones and tidy up the
implementation to prevent further eye bleed.

Make __default_send_IPI_shortcut() static as it has no other users.

Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
 arch/x86/kernel/apic/ipi.c   |   74 ++++++++++++++++++-------------------------
 arch/x86/kernel/apic/local.h |    2 -
 2 files changed, 32 insertions(+), 44 deletions(-)

--- a/arch/x86/kernel/apic/ipi.c
+++ b/arch/x86/kernel/apic/ipi.c
@@ -108,68 +108,58 @@ static inline void __xapic_wait_icr_idle
 		cpu_relax();
 }
 
-void __default_send_IPI_shortcut(unsigned int shortcut, int vector)
+/*
+ * This is safe against interruption because it only writes the lower 32
+ * bits of the APIC_ICR register. The destination field is ignored for
+ * short hand IPIs.
+ *
+ *  wait_icr_idle()
+ *  write(ICR2, dest)
+ *  NMI
+ *	wait_icr_idle()
+ *	write(ICR)
+ *	wait_icr_idle()
+ *  write(ICR)
+ *
+ * This function does not need to disable interrupts as there is no ICR2
+ * interaction. The memory write is direct except when the machine is
+ * affected by the 11AP Pentium erratum, which turns the plain write into
+ * an XCHG operation.
+ */
+static void __default_send_IPI_shortcut(unsigned int shortcut, int vector)
 {
 	/*
-	 * Subtle. In the case of the 'never do double writes' workaround
-	 * we have to lock out interrupts to be safe.  As we don't care
-	 * of the value read we use an atomic rmw access to avoid costly
-	 * cli/sti.  Otherwise we use an even cheaper single atomic write
-	 * to the APIC.
-	 */
-	unsigned int cfg;
-
-	/*
-	 * Wait for idle.
+	 * Wait for the previous ICR command to complete.  Use
+	 * safe_apic_wait_icr_idle() for the NMI vector as there have been
+	 * issues where otherwise the system hangs when the panic CPU tries
+	 * to stop the others before launching the kdump kernel.
 	 */
 	if (unlikely(vector == NMI_VECTOR))
 		safe_apic_wait_icr_idle();
 	else
 		__xapic_wait_icr_idle();
 
-	/*
-	 * No need to touch the target chip field. Also the destination
-	 * mode is ignored when a shorthand is used.
-	 */
-	cfg = __prepare_ICR(shortcut, vector, 0);
-
-	/*
-	 * Send the IPI. The write to APIC_ICR fires this off.
-	 */
-	native_apic_mem_write(APIC_ICR, cfg);
+	/* Destination field (ICR2) and the destination mode are ignored */
+	native_apic_mem_write(APIC_ICR, __prepare_ICR(shortcut, vector, 0));
 }
 
 /*
  * This is used to send an IPI with no shorthand notation (the destination is
  * specified in bits 56 to 63 of the ICR).
  */
-void __default_send_IPI_dest_field(unsigned int mask, int vector, unsigned int dest)
+void __default_send_IPI_dest_field(unsigned int dest_mask, int vector,
+				   unsigned int dest_mode)
 {
-	unsigned long cfg;
-
-	/*
-	 * Wait for idle.
-	 */
+	/* See comment in __default_send_IPI_shortcut() */
 	if (unlikely(vector == NMI_VECTOR))
 		safe_apic_wait_icr_idle();
 	else
 		__xapic_wait_icr_idle();
 
-	/*
-	 * prepare target chip field
-	 */
-	cfg = __prepare_ICR2(mask);
-	native_apic_mem_write(APIC_ICR2, cfg);
-
-	/*
-	 * program the ICR
-	 */
-	cfg = __prepare_ICR(0, vector, dest);
-
-	/*
-	 * Send the IPI. The write to APIC_ICR fires this off.
-	 */
-	native_apic_mem_write(APIC_ICR, cfg);
+	/* Set the IPI destination field in the ICR */
+	native_apic_mem_write(APIC_ICR2, __prepare_ICR2(dest_mask));
+	/* Send it with the proper destination mode */
+	native_apic_mem_write(APIC_ICR, __prepare_ICR(0, vector, dest_mode));
 }
 
 void default_send_IPI_single_phys(int cpu, int vector)
--- a/arch/x86/kernel/apic/local.h
+++ b/arch/x86/kernel/apic/local.h
@@ -44,8 +44,6 @@ static inline unsigned int __prepare_ICR
 
 void default_init_apic_ldr(void);
 
-void __default_send_IPI_shortcut(unsigned int shortcut, int vector);
-
 /*
  * This is used to send an IPI with no shorthand notation (the destination is
  * specified in bits 56 to 63 of the ICR).