linux-kernel - [PATCH v4] PCI/MSI: Forward MSI-X vector enable error code in pci_alloc_irq_vectors

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Date:   Tue, 16 Jun 2020 09:33:16 +0200
From:   Piotr Stankiewicz <piotr.stankiewicz@...el.com>
To:     Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org
Cc:     Piotr Stankiewicz <piotr.stankiewicz@...el.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Andrew Murray <amurray@...goodpenguin.co.uk>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Logan Gunthorpe <logang@...tatee.com>,
        Jian-Hong Pan <jian-hong@...lessm.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v4] PCI/MSI: Forward MSI-X vector enable error code in pci_alloc_irq_vectors_affinity()

When debugging an issue where I was asking the PCI machinery to enable a
set of MSI-X vectors, without falling back on MSI, I ran across a
behaviour which seems odd. The pci_alloc_irq_vectors_affinity() will
always return -ENOSPC on failure, when allocating MSI-X vectors only,
whereas with MSI fallback it will forward any error returned by
__pci_enable_msi_range(). This is a confusing behaviour, so have the
pci_alloc_irq_vectors_affinity() forward the error code from
__pci_enable_msix_range() when appropriate.

Signed-off-by: Piotr Stankiewicz <piotr.stankiewicz@...el.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@...el.com>
Reviewed-by: Logan Gunthorpe <logang@...tatee.com>
Reviewed-by: Christoph Hellwig <hch@....de>
---
 drivers/pci/msi.c | 22 +++++++++-------------
 1 file changed, 9 insertions(+), 13 deletions(-)

diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
index 6b43a5455c7a..cade9be68b09 100644
--- a/drivers/pci/msi.c
+++ b/drivers/pci/msi.c
@@ -1191,8 +1191,7 @@ int pci_alloc_irq_vectors_affinity(struct pci_dev *dev, unsigned int min_vecs,
 				   struct irq_affinity *affd)
 {
 	struct irq_affinity msi_default_affd = {0};
-	int msix_vecs = -ENOSPC;
-	int msi_vecs = -ENOSPC;
+	int nvecs = -ENOSPC;
 
 	if (flags & PCI_IRQ_AFFINITY) {
 		if (!affd)
@@ -1203,17 +1202,16 @@ int pci_alloc_irq_vectors_affinity(struct pci_dev *dev, unsigned int min_vecs,
 	}
 
 	if (flags & PCI_IRQ_MSIX) {
-		msix_vecs = __pci_enable_msix_range(dev, NULL, min_vecs,
-						    max_vecs, affd, flags);
-		if (msix_vecs > 0)
-			return msix_vecs;
+		nvecs = __pci_enable_msix_range(dev, NULL, min_vecs, max_vecs,
+						affd, flags);
+		if (nvecs > 0)
+			return nvecs;
 	}
 
 	if (flags & PCI_IRQ_MSI) {
-		msi_vecs = __pci_enable_msi_range(dev, min_vecs, max_vecs,
-						  affd);
-		if (msi_vecs > 0)
-			return msi_vecs;
+		nvecs = __pci_enable_msi_range(dev, min_vecs, max_vecs, affd);
+		if (nvecs > 0)
+			return nvecs;
 	}
 
 	/* use legacy IRQ if allowed */
@@ -1231,9 +1229,7 @@ int pci_alloc_irq_vectors_affinity(struct pci_dev *dev, unsigned int min_vecs,
 		}
 	}
 
-	if (msix_vecs == -ENOSPC)
-		return -ENOSPC;
-	return msi_vecs;
+	return nvecs;
 }
 EXPORT_SYMBOL(pci_alloc_irq_vectors_affinity);
 
-- 
2.17.2