[PATCH] powerpc: Fix loss of interrupts with MPIC

With the new interrupt rework, an interrupt "host" map() callback can be
called after the interrupt is already active.

It's called again for an already mapped interrupt to allow changing the
trigger setup, and currently this is not guarded with a test of wether
the interrupt is requested or not.

I plan to change some of this logic to be a bit less lenient against
random reconfiguring of live interrupts but just not yet.

The ported MPIC driver has a bug where when that happens, it will mask
the interrupt. This changes it to preserve the previous masking of the
interrupt instead.

Signed-off-by: Benjamin Herrenschmidt <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

arch/powerpc/sysdev/mpic.c

···
 	unsigned int loops = 100000;
 	struct mpic *mpic = mpic_from_irq(irq);
 	unsigned int src = mpic_irq_to_hw(irq);
+	unsigned long flags;
 
 	DBG("%p: %s: enable_irq: %d (src %d)\n", mpic, mpic->name, irq, src);
 
+	spin_lock_irqsave(&mpic_lock, flags);
 	mpic_irq_write(src, MPIC_IRQ_VECTOR_PRI,
 		       mpic_irq_read(src, MPIC_IRQ_VECTOR_PRI) &
 		       ~MPIC_VECPRI_MASK);
-
 	/* make sure mask gets to controller before we return to user */
 	do {
 		if (!loops--) {
 			printk(KERN_ERR "mpic_enable_irq timeout\n");
 			break;
 		}
-	} while(mpic_irq_read(src, MPIC_IRQ_VECTOR_PRI) & MPIC_VECPRI_MASK);	
+	} while(mpic_irq_read(src, MPIC_IRQ_VECTOR_PRI) & MPIC_VECPRI_MASK);
+	spin_unlock_irqrestore(&mpic_lock, flags);
 }
 
 static void mpic_mask_irq(unsigned int irq)
···
 	unsigned int loops = 100000;
 	struct mpic *mpic = mpic_from_irq(irq);
 	unsigned int src = mpic_irq_to_hw(irq);
+	unsigned long flags;
 
 	DBG("%s: disable_irq: %d (src %d)\n", mpic->name, irq, src);
 
+	spin_lock_irqsave(&mpic_lock, flags);
 	mpic_irq_write(src, MPIC_IRQ_VECTOR_PRI,
 		       mpic_irq_read(src, MPIC_IRQ_VECTOR_PRI) |
 		       MPIC_VECPRI_MASK);
···
 			break;
 		}
 	} while(!(mpic_irq_read(src, MPIC_IRQ_VECTOR_PRI) & MPIC_VECPRI_MASK));
+	spin_unlock_irqrestore(&mpic_lock, flags);
 }
 
 static void mpic_end_irq(unsigned int irq)
···
 	struct irq_desc *desc = get_irq_desc(virq);
 	struct irq_chip *chip;
 	struct mpic *mpic = h->host_data;
-	unsigned int vecpri = MPIC_VECPRI_SENSE_LEVEL |
+	u32 v, vecpri = MPIC_VECPRI_SENSE_LEVEL |
 		MPIC_VECPRI_POLARITY_NEGATIVE;
 	int level;
+	unsigned long iflags;
 
 	pr_debug("mpic: map virq %d, hwirq 0x%lx, flags: 0x%x\n",
 		 virq, hw, flags);
···
 	}
 #endif
 
-	/* Reconfigure irq */
-	vecpri |= MPIC_VECPRI_MASK | hw | (8 << MPIC_VECPRI_PRIORITY_SHIFT);
-	mpic_irq_write(hw, MPIC_IRQ_VECTOR_PRI, vecpri);
+	/* Reconfigure irq. We must preserve the mask bit as we can be called
+	 * while the interrupt is still active (This may change in the future
+	 * but for now, it is the case).
+	 */
+	spin_lock_irqsave(&mpic_lock, iflags);
+	v = mpic_irq_read(hw, MPIC_IRQ_VECTOR_PRI);
+	vecpri = (v &
+		~(MPIC_VECPRI_POLARITY_MASK | MPIC_VECPRI_SENSE_MASK)) |
+		vecpri;
+	if (vecpri != v)
+		mpic_irq_write(hw, MPIC_IRQ_VECTOR_PRI, vecpri);
+	spin_unlock_irqrestore(&mpic_lock, iflags);
 
-	pr_debug("mpic: mapping as IRQ\n");
+	pr_debug("mpic: mapping as IRQ, vecpri = 0x%08x (was 0x%08x)\n",
+		 vecpri, v);
 
 	set_irq_chip_data(virq, mpic);
 	set_irq_chip_and_handler(virq, chip, handle_fasteoi_irq);
···
 		
 		/* do senses munging */
 		if (mpic->senses && i < mpic->senses_count)
-			vecpri = mpic_flags_to_vecpri(mpic->senses[i],
-						      &level);
+			vecpri |= mpic_flags_to_vecpri(mpic->senses[i],
+						       &level);
 		else
 			vecpri |= MPIC_VECPRI_SENSE_LEVEL;
 
···
 
 void __init mpic_set_serial_int(struct mpic *mpic, int enable)
 {
+	unsigned long flags;
 	u32 v;
 
+	spin_lock_irqsave(&mpic_lock, flags);
 	v = mpic_read(mpic->gregs, MPIC_GREG_GLOBAL_CONF_1);
 	if (enable)
 		v |= MPIC_GREG_GLOBAL_CONF_1_SIE;
 	else
 		v &= ~MPIC_GREG_GLOBAL_CONF_1_SIE;
 	mpic_write(mpic->gregs, MPIC_GREG_GLOBAL_CONF_1, v);
+	spin_unlock_irqrestore(&mpic_lock, flags);
 }
 
 void mpic_irq_set_priority(unsigned int irq, unsigned int pri)