x86/irq: Save destination CPU ID in irq_cfg

Cache destination CPU APIC ID into struct irq_cfg when assigning vector
for interrupt. Upper layer just needs to read the cached APIC ID instead
of calling apic->cpu_mask_to_apicid_and(), it helps to hide APIC driver
details from IOAPIC/HPET/MSI drivers..

Signed-off-by: Jiang Liu <jiang.liu@linux.intel.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: David Cohen <david.a.cohen@linux.intel.com>
Cc: Sander Eikelenboom <linux@eikelenboom.it>
Cc: David Vrabel <david.vrabel@citrix.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Rafael J. Wysocki <rjw@rjwysocki.net>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Yinghai Lu <yinghai@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dimitri Sivanich <sivanich@sgi.com>
Link: http://lkml.kernel.org/r/1428905519-23704-2-git-send-email-jiang.liu@linux.intel.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/include/asm/hw_irq.h

@@ -116,6 +116,7 @@ struct irq_data;
 struct irq_cfg {
 	cpumask_var_t		domain;
 	cpumask_var_t		old_domain;
+	unsigned int		dest_apicid;
 	u8			vector;
 	u8			move_in_progress : 1;
 #ifdef CONFIG_IRQ_REMAP

arch/x86/kernel/apic/vector.c

@@ -188,6 +188,12 @@ next:
 	}
 	free_cpumask_var(tmp_mask);
 
+	if (!err) {
+		/* cache destination APIC IDs into cfg->dest_apicid */
+		err = apic->cpu_mask_to_apicid_and(mask, cfg->domain,
+						   &cfg->dest_apicid);
+	}
+
 	return err;
 }