[tip: irq/core] genirq/msi: Provide MSI_FLAG_MSIX_ALLOC_DYN

[tip-bot2 for Thomas Gleixner]

The following commit has been merged into the irq/core branch of tip:

Commit-ID:     b834e3c08fc6c4460c2bce6575cba4705f6301e3
Gitweb:        https://git.kernel.org/tip/b834e3c08fc6c4460c2bce6575cba4705f6301e3
Author:        Thomas Gleixner <tglx@xxxxxxxxxxxxx>
AuthorDate:    Fri, 25 Nov 2022 00:26:20 +01:00
Committer:     Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitterDate: Mon, 05 Dec 2022 22:22:34 +01:00

genirq/msi: Provide MSI_FLAG_MSIX_ALLOC_DYN

Provide a new MSI feature flag in preparation for dynamic MSIX allocation
after the initial MSI-X enable has been done.

This needs to be an explicit MSI interrupt domain feature because quite
some implementations (both interrupt domains and legacy allocation mode)
have clear expectations that the allocation code is only invoked when MSI-X
is about to be enabled. They either talk to hypervisors or do some other
work and are not prepared to be invoked on an already MSI-X enabled device.

This is also explicit MSI-X only because rewriting the size of the MSI
entries is only possible when disabling MSI which in turn might cause lost
interrupts on the device.

Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>
Acked-by: Marc Zyngier <maz@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20221124232326.558843119@xxxxxxxxxxxxx

---
 include/linux/msi.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/linux/msi.h b/include/linux/msi.h
index 00c5019..3cb1586 100644
--- a/include/linux/msi.h
+++ b/include/linux/msi.h
@@ -557,7 +557,8 @@ enum {
 	MSI_FLAG_LEVEL_CAPABLE		= (1 << 18),
 	/* MSI-X entries must be contiguous */
 	MSI_FLAG_MSIX_CONTIGUOUS	= (1 << 19),
-
+	/* PCI/MSI-X vectors can be dynamically allocated/freed post MSI-X enable */
+	MSI_FLAG_PCI_MSIX_ALLOC_DYN	= (1 << 20),
 };
 
 /**