genirq/msi: Move prepare() call to per-device allocation

JIRA: https://issues.redhat.com/browse/RHEL-120705
Upstream Status: 1396e89

commit 1396e89
Author: Marc Zyngier <maz@kernel.org>
Date:   Tue May 13 17:31:42 2025 +0100

    genirq/msi: Move prepare() call to per-device allocation

    The current device MSI infrastructure is subtly broken, as it will issue an
    .msi_prepare() callback into the MSI controller driver every time it needs
    to allocate an MSI. That's pretty wrong, as the contract (or unwarranted
    assumption, depending who you ask) between the MSI controller and the core
    code is that .msi_prepare() is called exactly once per device.

    This leads to some subtle breakage in some MSI controller drivers, as it
    gives the impression that there are multiple endpoints sharing a bus
    identifier (RID in PCI parlance, DID for GICv3+). It implies that whatever
    allocation the ITS driver (for example) has done on behalf of these devices
    cannot be undone, as there is no way to track the shared state. This is
    particularly bad for wire-MSI devices, for which .msi_prepare() is called
    for each input line.

    To address this issue, move the call to .msi_prepare() to take place at the
    point of irq domain allocation, which is the only place that makes
    sense. The msi_alloc_info_t structure is made part of the
    msi_domain_template, so that its life-cycle is that of the domain as well.

    Finally, the msi_info::alloc_data field is made to point at this allocation
    tracking structure, ensuring that it is carried around the block.

    This is all pretty straightforward, except for the non-device-MSI
    leftovers, which still have to call .msi_prepare() at the old spot. One
    day...

    Signed-off-by: Marc Zyngier <maz@kernel.org>
    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Link: https://lore.kernel.org/all/20250513163144.2215824-4-maz@kernel.org

Signed-off-by: Myron Stowe <mstowe@redhat.com>

Author: Myron Stowe

include/linux/msi.h

@@ -516,12 +516,14 @@ struct msi_domain_info {
  * @chip:	Interrupt chip for this domain
  * @ops:	MSI domain ops
  * @info:	MSI domain info data
+ * @alloc_info:	MSI domain allocation data (architecture specific)
  */
 struct msi_domain_template {
 	char			name[48];
 	struct irq_chip		chip;
 	struct msi_domain_ops	ops;
 	struct msi_domain_info	info;
+	msi_alloc_info_t	alloc_info;
 };
 
 /*

kernel/irq/msi.c

@@ -58,7 +58,8 @@ struct msi_ctrl {
 static void msi_domain_free_locked(struct device *dev, struct msi_ctrl *ctrl);
 static unsigned int msi_domain_get_hwsize(struct device *dev, unsigned int domid);
 static inline int msi_sysfs_create_group(struct device *dev);
-
+static int msi_domain_prepare_irqs(struct irq_domain *domain, struct device *dev,
+				   int nvec, msi_alloc_info_t *arg);
 
 /**
  * msi_alloc_desc - Allocate an initialized msi_desc
@@ -1004,6 +1005,7 @@ bool msi_create_device_irq_domain(struct device *dev, unsigned int domid,
 	bundle->info.ops = &bundle->ops;
 	bundle->info.data = domain_data;
 	bundle->info.chip_data = chip_data;
+	bundle->info.alloc_data = &bundle->alloc_info;
 
 	pops = parent->msi_parent_ops;
 	snprintf(bundle->name, sizeof(bundle->name), "%s%s-%s",
@@ -1042,11 +1044,18 @@ bool msi_create_device_irq_domain(struct device *dev, unsigned int domid,
 	if (!domain)
 		return false;
 
+	domain->dev = dev;
+	dev->msi.data->__domains[domid].domain = domain;
+
+	if (msi_domain_prepare_irqs(domain, dev, hwsize, &bundle->alloc_info)) {
+		dev->msi.data->__domains[domid].domain = NULL;
+		irq_domain_remove(domain);
+		return false;
+	}
+
 	/* @bundle and @fwnode_alloced are now in use. Prevent cleanup */
 	retain_and_null_ptr(bundle);
 	retain_and_null_ptr(fwnode_alloced);
-	domain->dev = dev;
-	dev->msi.data->__domains[domid].domain = domain;
 	return true;
 }
 
@@ -1213,6 +1222,24 @@ static int msi_init_virq(struct irq_domain *domain, int virq, unsigned int vflag
 	return 0;
 }
 
+static int populate_alloc_info(struct irq_domain *domain, struct device *dev,
+			       unsigned int nirqs, msi_alloc_info_t *arg)
+{
+	struct msi_domain_info *info = domain->host_data;
+
+	/*
+	 * If the caller has provided a template alloc info, use that. Once
+	 * all users of msi_create_irq_domain() have been eliminated, this
+	 * should be the only source of allocation information, and the
+	 * prepare call below should be finally removed.
+	 */
+	if (!info->alloc_data)
+		return msi_domain_prepare_irqs(domain, dev, nirqs, arg);
+
+	*arg = *info->alloc_data;
+	return 0;
+}
+
 static int __msi_domain_alloc_irqs(struct device *dev, struct irq_domain *domain,
 				   struct msi_ctrl *ctrl)
 {
@@ -1225,7 +1252,7 @@ static int __msi_domain_alloc_irqs(struct device *dev, struct irq_domain *domain
 	unsigned long idx;
 	int i, ret, virq;
 
-	ret = msi_domain_prepare_irqs(domain, dev, ctrl->nirqs, &arg);
+	ret = populate_alloc_info(domain, dev, ctrl->nirqs, &arg);
 	if (ret)
 		return ret;