powerpc/pseries: Fix MSI-X allocation failure when quota is exceeded

Nilay reported that since commit daaa574 ("powerpc/pseries/msi: Switch
to msi_create_parent_irq_domain()"), the NVMe driver cannot enable MSI-X
when the device's MSI-X table size is larger than the firmware's MSI quota
for the device.

This is because the commit changes how rtas_prepare_msi_irqs() is called:

  - Before, it is called when interrupts are allocated at the global
    interrupt domain with nvec_in being the number of allocated interrupts.
    rtas_prepare_msi_irqs() can return a positive number and the allocation
    will be retried.

  - Now, it is called at the creation of per-device interrupt domain with
    nvec_in being the number of interrupts that the device supports. If
    rtas_prepare_msi_irqs() returns positive, domain creation just fails.

For Nilay's NVMe driver case, rtas_prepare_msi_irqs() returns a positive
number (the quota). This causes per-device interrupt domain creation to
fail and thus the NVMe driver cannot enable MSI-X.

Rework to make this scenario works again:

  - pseries_msi_ops_prepare() only prepares as many interrupts as the quota
    permit.

  - pseries_irq_domain_alloc() fails if the device's quota is exceeded.

Now, if the quota is exceeded, pseries_msi_ops_prepare() will only prepare
as allowed by the quota. If device drivers attempt to allocate more
interrupts than the quota permits, pseries_irq_domain_alloc() will return
an error code and msi_handle_pci_fail() will allow device drivers a retry.

Reported-by: Nilay Shroff <nilay@linux.ibm.com>
Closes: https://lore.kernel.org/linuxppc-dev/6af2c4c2-97f6-4758-be33-256638ef39e5@linux.ibm.com/
Fixes: daaa574 ("powerpc/pseries/msi: Switch to msi_create_parent_irq_domain()")
Signed-off-by: Nam Cao <namcao@linutronix.de>
Cc: stable@vger.kernel.org
Tested-by: Nilay Shroff <nilay@linux.ibm.com>
Acked-by: Nilay Shroff <nilay@linux.ibm.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20260107100230.1466093-1-namcao@linutronix.de

Author: covanam

arch/powerpc/platforms/pseries/msi.c

@@ -19,6 +19,11 @@
 
 #include "pseries.h"
 
+struct pseries_msi_device {
+	unsigned int msi_quota;
+	unsigned int msi_used;
+};
+
 static int query_token, change_token;
 
 #define RTAS_QUERY_FN		0
@@ -433,8 +438,28 @@ static int pseries_msi_ops_prepare(struct irq_domain *domain, struct device *dev
 	struct msi_domain_info *info = domain->host_data;
 	struct pci_dev *pdev = to_pci_dev(dev);
 	int type = (info->flags & MSI_FLAG_PCI_MSIX) ? PCI_CAP_ID_MSIX : PCI_CAP_ID_MSI;
+	int ret;
+
+	struct pseries_msi_device *pseries_dev __free(kfree)
+		= kmalloc(sizeof(*pseries_dev), GFP_KERNEL);
+	if (!pseries_dev)
+		return -ENOMEM;
+
+	while (1) {
+		ret = rtas_prepare_msi_irqs(pdev, nvec, type, arg);
+		if (!ret)
+			break;
+		else if (ret > 0)
+			nvec = ret;
+		else
+			return ret;
+	}
 
-	return rtas_prepare_msi_irqs(pdev, nvec, type, arg);
+	pseries_dev->msi_quota = nvec;
+	pseries_dev->msi_used = 0;
+
+	arg->scratchpad[0].ptr = no_free_ptr(pseries_dev);
+	return 0;
 }
 
 /*
@@ -443,9 +468,13 @@ static int pseries_msi_ops_prepare(struct irq_domain *domain, struct device *dev
  */
 static void pseries_msi_ops_teardown(struct irq_domain *domain, msi_alloc_info_t *arg)
 {
+	struct pseries_msi_device *pseries_dev = arg->scratchpad[0].ptr;
 	struct pci_dev *pdev = to_pci_dev(domain->dev);
 
 	rtas_disable_msi(pdev);
+
+	WARN_ON(pseries_dev->msi_used);
+	kfree(pseries_dev);
 }
 
 static void pseries_msi_shutdown(struct irq_data *d)
@@ -546,12 +575,18 @@ static int pseries_irq_domain_alloc(struct irq_domain *domain, unsigned int virq
 				    unsigned int nr_irqs, void *arg)
 {
 	struct pci_controller *phb = domain->host_data;
+	struct pseries_msi_device *pseries_dev;
 	msi_alloc_info_t *info = arg;
 	struct msi_desc *desc = info->desc;
 	struct pci_dev *pdev = msi_desc_to_pci_dev(desc);
 	int hwirq;
 	int i, ret;
 
+	pseries_dev = info->scratchpad[0].ptr;
+
+	if (pseries_dev->msi_used + nr_irqs > pseries_dev->msi_quota)
+		return -ENOSPC;
+
 	hwirq = rtas_query_irq_number(pci_get_pdn(pdev), desc->msi_index);
 	if (hwirq < 0) {
 		dev_err(&pdev->dev, "Failed to query HW IRQ: %d\n", hwirq);
@@ -567,9 +602,10 @@ static int pseries_irq_domain_alloc(struct irq_domain *domain, unsigned int virq
 			goto out;
 
 		irq_domain_set_hwirq_and_chip(domain, virq + i, hwirq + i,
-					      &pseries_msi_irq_chip, domain->host_data);
+					      &pseries_msi_irq_chip, pseries_dev);
 	}
 
+	pseries_dev->msi_used++;
 	return 0;
 
 out:
@@ -582,9 +618,11 @@ static void pseries_irq_domain_free(struct irq_domain *domain, unsigned int virq
 				    unsigned int nr_irqs)
 {
 	struct irq_data *d = irq_domain_get_irq_data(domain, virq);
-	struct pci_controller *phb = irq_data_get_irq_chip_data(d);
+	struct pseries_msi_device *pseries_dev = irq_data_get_irq_chip_data(d);
+	struct pci_controller *phb = domain->host_data;
 
 	pr_debug("%s bridge %pOF %d #%d\n", __func__, phb->dn, virq, nr_irqs);
+	pseries_dev->msi_used -= nr_irqs;
 	irq_domain_free_irqs_parent(domain, virq, nr_irqs);
 }