powerpc: Add code to handle soft-disabled doorbells on server

This patch adds the logic to properly handle doorbells that come in when
interrupts have been soft disabled and to replay them when interrupts
are re-enabled:

- masked_##_H##interrupt is modified to leave interrupts enabled when a
doorbell has come in since doorbells are edge sensitive and as such
won't be automatically re-raised.

- __check_irq_replay now tests if a doorbell happened on book3s, and
returns either 0xe80 or 0xa00 depending on whether we are the
hypervisor or not.

- restore_check_irq_replay now tests for the two possible server
doorbell vector numbers to replay.

- __replay_interrupt also adds tests for the two server doorbell vector
numbers, and is modified to use a compare instruction rather than an
andi. on the single bit difference between 0x500 and 0x900.

The last two use a CPU feature section to avoid needlessly testing
against the hypervisor vector if it is not the hypervisor, and vice
versa.

Signed-off-by: Ian Munsie <[e-mail]>
Signed-off-by: Benjamin Herrenschmidt <[e-mail]>

arch/powerpc/kernel/entry_64.S

···
 	addi	r3,r1,STACK_FRAME_OVERHEAD;
 	bl	.timer_interrupt
 	b	.ret_from_except
+#ifdef CONFIG_PPC_DOORBELL
+1:
 #ifdef CONFIG_PPC_BOOK3E
-1:	cmpwi	cr0,r3,0x280
+	cmpwi	cr0,r3,0x280
+#else
+	BEGIN_FTR_SECTION
+		cmpwi	cr0,r3,0xe80
+	FTR_SECTION_ELSE
+		cmpwi	cr0,r3,0xa00
+	ALT_FTR_SECTION_END_IFSET(CPU_FTR_HVMODE)
+#endif /* CONFIG_PPC_BOOK3E */
 	bne	1f
 	addi	r3,r1,STACK_FRAME_OVERHEAD;
 	bl	.doorbell_exception
 	b	.ret_from_except
-#endif /* CONFIG_PPC_BOOK3E */
+#endif /* CONFIG_PPC_DOORBELL */
 1:	b	.ret_from_except /* What else to do here ? */
  
 unrecov_restore:

arch/powerpc/kernel/exceptions-64s.S

···
 	KVM_HANDLER_PR(PACA_EXGEN, EXC_STD, 0xf40)
 
 /*
- * An interrupt came in while soft-disabled. We set paca->irq_happened,
- * then, if it was a decrementer interrupt, we bump the dec to max and
- * and return, else we hard disable and return. This is called with
- * r10 containing the value to OR to the paca field.
+ * An interrupt came in while soft-disabled. We set paca->irq_happened, then:
+ * - If it was a decrementer interrupt, we bump the dec to max and and return.
+ * - If it was a doorbell we return immediately since doorbells are edge
+ *   triggered and won't automatically refire.
+ * - else we hard disable and return.
+ * This is called with r10 containing the value to OR to the paca field.
  */
 #define MASKED_INTERRUPT(_H)				\
 masked_##_H##interrupt:					\
···
 	lbz	r11,PACAIRQHAPPENED(r13);		\
 	or	r11,r11,r10;				\
 	stb	r11,PACAIRQHAPPENED(r13);		\
-	andi.	r10,r10,PACA_IRQ_DEC;			\
-	beq	1f;					\
+	cmpwi	r10,PACA_IRQ_DEC;			\
+	bne	1f;					\
 	lis	r10,0x7fff;				\
 	ori	r10,r10,0xffff;				\
 	mtspr	SPRN_DEC,r10;				\
 	b	2f;					\
-1:	mfspr	r10,SPRN_##_H##SRR1;			\
+1:	cmpwi	r10,PACA_IRQ_DBELL;			\
+	beq	2f;					\
+	mfspr	r10,SPRN_##_H##SRR1;			\
 	rldicl	r10,r10,48,1; /* clear MSR_EE */	\
 	rotldi	r10,r10,16;				\
 	mtspr	SPRN_##_H##SRR1,r10;			\
···
 
 /*
  * Called from arch_local_irq_enable when an interrupt needs
- * to be resent. r3 contains 0x500 or 0x900 to indicate which
- * kind of interrupt. MSR:EE is already off. We generate a
+ * to be resent. r3 contains 0x500, 0x900, 0xa00 or 0xe80 to indicate
+ * which kind of interrupt. MSR:EE is already off. We generate a
  * stackframe like if a real interrupt had happened.
  *
  * Note: While MSR:EE is off, we need to make sure that _MSR
···
 	mflr	r11
 	mfcr	r9
 	ori	r12,r12,MSR_EE
-	andi.	r3,r3,0x0800
-	bne	decrementer_common
-	b	hardware_interrupt_common
+	cmpwi	r3,0x900
+	beq	decrementer_common
+	cmpwi	r3,0x500
+	beq	hardware_interrupt_common
+BEGIN_FTR_SECTION
+	cmpwi	r3,0xe80
+	beq	h_doorbell_common
+FTR_SECTION_ELSE
+	cmpwi	r3,0xa00
+	beq	doorbell_super_common
+ALT_FTR_SECTION_END_IFSET(CPU_FTR_HVMODE)
+	blr
 
 #ifdef CONFIG_PPC_PSERIES
 /*

arch/powerpc/kernel/irq.c

···
 }
 
 /* This is called whenever we are re-enabling interrupts
- * and returns either 0 (nothing to do) or 500/900 if there's
- * either an EE or a DEC to generate.
+ * and returns either 0 (nothing to do) or 500/900/280/a00/e80 if
+ * there's an EE, DEC or DBELL to generate.
  *
  * This is called in two contexts: From arch_local_irq_restore()
  * before soft-enabling interrupts, and from the exception exit
···
 	local_paca->irq_happened &= ~PACA_IRQ_DBELL;
 	if (happened & PACA_IRQ_DBELL)
 		return 0x280;
+#else
+	local_paca->irq_happened &= ~PACA_IRQ_DBELL;
+	if (happened & PACA_IRQ_DBELL) {
+		if (cpu_has_feature(CPU_FTR_HVMODE))
+			return 0xe80;
+		return 0xa00;
+	}
 #endif /* CONFIG_PPC_BOOK3E */
 
 	/* There should be nothing left ! */