[PATCH RFC 04/13] iommu/vt-d: Add helper and flag to check/disable posted MSI

[Jacob Pan <jacob.jun.pan@linux.intel.com>]

Allow command line opt-out posted MSI under CONFIG_X86_POSTED_MSI=y.
And add a helper function for testing if posted MSI is supported on the
CPU side.

Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
---
 arch/x86/include/asm/irq_remapping.h | 11 +++++++++++
 drivers/iommu/irq_remapping.c        | 17 +++++++++++++++++
 2 files changed, 28 insertions(+)

diff --git a/arch/x86/include/asm/irq_remapping.h b/arch/x86/include/asm/irq_remapping.h
index 7a2ed154a5e1..706f58900962 100644
--- a/arch/x86/include/asm/irq_remapping.h
+++ b/arch/x86/include/asm/irq_remapping.h
@@ -50,6 +50,17 @@ static inline struct irq_domain *arch_get_ir_parent_domain(void)
 	return x86_vector_domain;
 }
 
+#ifdef CONFIG_X86_POSTED_MSI
+extern unsigned int posted_msi_off;
+
+static inline bool posted_msi_supported(void)
+{
+	return !posted_msi_off && irq_remapping_cap(IRQ_POSTING_CAP);
+}
+#else
+static inline bool posted_msi_supported(void) { return false; };
+#endif
+
 #else  /* CONFIG_IRQ_REMAP */
 
 static inline bool irq_remapping_cap(enum irq_remap_cap cap) { return 0; }
diff --git a/drivers/iommu/irq_remapping.c b/drivers/iommu/irq_remapping.c
index 83314b9d8f38..00de6963bb07 100644
--- a/drivers/iommu/irq_remapping.c
+++ b/drivers/iommu/irq_remapping.c
@@ -24,6 +24,23 @@ int no_x2apic_optout;
 
 int disable_irq_post = 0;
 
+#ifdef CONFIG_X86_POSTED_MSI
+
+unsigned int posted_msi_off;
+
+static int __init cmdl_posted_msi_off(char *str)
+{
+	int value = 0;
+
+	get_option(&str, &value);
+	posted_msi_off = value;
+
+	return 1;
+}
+
+__setup("posted_msi_off=", cmdl_posted_msi_off);
+#endif
+
 static int disable_irq_remap;
 static struct irq_remap_ops *remap_ops;
 
-- 
2.25.1