genirq/msi: Convert storage to xarray

The current linked list storage for MSI descriptors is suboptimal in
several ways:

  1) Looking up a MSI desciptor requires a O(n) list walk in the worst case

  2) The upcoming support of runtime expansion of MSI-X vectors would need
     to do a full list walk to figure out whether a particular index is
     already associated.

  3) Runtime expansion of sparse allocations is even more complex as the
     current implementation assumes an ordered list (increasing MSI index).

Use an xarray which solves all of the above problems nicely.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Michael Kelley <mikelley@microsoft.com>
Tested-by: Nishanth Menon <nm@ti.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/20211206210749.280627070@linutronix.de

1 files changed, 6 insertions, 7 deletions

diff --git a/include/linux/msi.h b/include/linux/msi.h
index 1a00367d2cfa..fc918a658d48 100644
--- a/include/linux/msi.h
+++ b/include/linux/msi.h
@@ -17,6 +17,7 @@
  */
 
 #include <linux/cpumask.h>
+#include <linux/xarray.h>
 #include <linux/mutex.h>
 #include <linux/list.h>
 #include <asm/msi.h>
@@ -123,7 +124,6 @@ struct pci_msi_desc {
 
 /**
  * struct msi_desc - Descriptor structure for MSI based interrupts
- * @list:	List head for management
  * @irq:	The base interrupt number
  * @nvec_used:	The number of vectors used
  * @dev:	Pointer to the device which uses this descriptor
@@ -140,7 +140,6 @@ struct pci_msi_desc {
  */
 struct msi_desc {
 	/* Shared device/bus type independent data */
-	struct list_head		list;
 	unsigned int			irq;
 	unsigned int			nvec_used;
 	struct device			*dev;
@@ -176,16 +175,16 @@ enum msi_desc_filter {
  * msi_device_data - MSI per device data
  * @properties:		MSI properties which are interesting to drivers
  * @platform_data:	Platform-MSI specific data
- * @list:		List of MSI descriptors associated to the device
- * @mutex:		Mutex protecting the MSI list
- * @__next:		Cached pointer to the next entry for iterators
+ * @mutex:		Mutex protecting the MSI descriptor store
+ * @__store:		Xarray for storing MSI descriptor pointers
+ * @__iter_idx:		Index to search the next entry for iterators
  */
 struct msi_device_data {
 	unsigned long			properties;
 	struct platform_msi_priv_data	*platform_data;
-	struct list_head		list;
 	struct mutex			mutex;
-	struct msi_desc			*__next;
+	struct xarray			__store;
+	unsigned long			__iter_idx;
 };
 
 int msi_setup_device_data(struct device *dev);