Re: [PATCH v4 2/2] powerpc: make MPIC honor the "pic-no-reset" device tree property

On 03/01/2011 09:22 PM, Benjamin Herrenschmidt wrote:

quoted

diff --git a/arch/powerpc/include/asm/mpic.h b/arch/powerpc/include/asm/mpic.h
index e000cce..7e1be12 100644
--- a/arch/powerpc/include/asm/mpic.h
+++ b/arch/powerpc/include/asm/mpic.h

@@ -325,6 +325,8 @@ struct mpic
  #ifdef CONFIG_PM
  	struct mpic_irq_save	*save_data;
  #endif
+
+	int cpu;
  };

Why ? The MPIC isn't specifically associated with a CPU and whatever we
pick as default during boot isn't relevant later on, so I don't see why
we should have global permanent state here.

I agree.  I shouldn't have cached that.  We should probably introduce a helper function to get the cpuid, though.  The:

	unsigned int cpu = 0;

	if (mpic->flags & MPIC_PRIMARY)
		cpu = hard_smp_processor_id();

code is scattered in three places: '_mpic_cpu_write', '_mpic_cpu_read', and 'mpic_init'.

quoted

  /* Check if we have one of those nice broken MPICs with a flipped endian on

@@ -622,6 +631,14 @@ static unsigned int mpic_is_ipi(struct mpic *mpic, unsigned int irq)
  	return (src>= mpic->ipi_vecs[0]&&  src<= mpic->ipi_vecs[3]);
  }

+/* Determine if the linux irq is a timer interrupt */
+static unsigned int mpic_is_timer_interrupt(struct mpic *mpic, unsigned int irq)
+{
+	unsigned int src = mpic_irq_to_hw(irq);
+
+	return (src>= mpic->timer_vecs[0]&&  src<= mpic->timer_vecs[3]);
+}
+

  /* Convert a cpu mask from logical to physical cpu numbers. */
  static inline u32 mpic_physmask(u32 cpumask)

@@ -967,6 +984,15 @@ static int mpic_host_map(struct irq_host *h, unsigned int virq,
  	if (hw>= mpic->irq_count)
  		return -EINVAL;

+	/* If the MPIC was reset, then all vectors have already been
+	 * initialized.  Otherwise, the appropriate vector needs to be
+	 * initialized here to ensure that only used sources are setup with
+	 * a vector.
+	 */
+	if (mpic->flags&  MPIC_NO_RESET)
+		if (!(mpic_is_ipi(mpic, hw) || mpic_is_timer_interrupt(mpic, hw)))
+			mpic_init_vector(mpic, hw);
+

The above isn't useful. Of those two registers you want to initialize,
afaik, one (the destination) will be initialized by the core calling
into set_affinity when the interrupt is requested, and the other one is

AFAIK, we can't rely on 'set_affinity' always being called.  I don't think it is called at all when !defined(CONFIG_SMP) and if it was, then that would be an error:

	/* include/linux/irq.h */

	#else /* CONFIG_SMP */

	static inline int irq_set_affinity(unsigned int irq,
		const struct cpumask *m)
	{
		return -EINVAL;
	}

partially initialized in set_type, I'd say just modify set_type to
initialize the source as well, and problem solved, no ?

The priority has to be initialized as well.  They could both be done in 'mpic_set_irq_type', but that seems like a weird place since it has nothing to do with actually setting the type.

Since we already have 'mpic_irq_set_priority' and 'mpic_set_vector', perhaps a better option is to add 'mpic_set_destination' and put the following in 'mpic_host_map' (using the cpuid helper function suggested above):

	/* Lazy source init when MPIC_NO_RESET */
	if (!mpic_is_ipi(mpic, hw) && (mpic->flags & MPIC_NO_RESET)) {
		mpic_set_vector(virq, hw);
		mpic_set_destination(virq, mpic_cpuid(mpic));
		mpic_irq_set_priority(virq, 8);
	}

It is more overhead, but it reads well.  Thoughts?

Or is there a chance that the interrupt was left unmasked ?

There shouldn't be.  The original idea was that either the boot program would leave it masked or one of the AMP OSes would boot without 'pic-no-reset', which would mask everything.  Most likely the boot program.

I think it would be kosher to mask it in set_type unconditionally, I don't think it's ever supposed
to be called for an enabled interrupt.

I will look into that.

Thanks,

-- 
Meador Inge     | meador_inge AT mentor.com
Mentor Embedded | http://www.mentor.com/embedded-software