linux-kernel - [PATCH 1/2] PCI: MSI: Deal with devices lying about their MSI mask capability

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Message-Id: <20211104180130.3825416-2-maz@kernel.org>
Date:   Thu,  4 Nov 2021 18:01:29 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Rui Salvaterra <rsalvaterra@...il.com>, kernel-team@...roid.com
Subject: [PATCH 1/2] PCI: MSI: Deal with devices lying about their MSI mask capability

It appears that some devices are lying about their mask capability,
pretending that they don't have it, while they actually do.
The net result is that now that we don't enable MSIs on such
endpoint.

Add a new per-device flag to deal with this. Further patches will
make use of it, sadly.

Signed-off-by: Marc Zyngier <maz@...nel.org>
---
 drivers/pci/msi.c   | 3 +++
 include/linux/pci.h | 2 ++
 2 files changed, 5 insertions(+)

diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
index 0099a00af361..2f9ec7210991 100644
--- a/drivers/pci/msi.c
+++ b/drivers/pci/msi.c
@@ -479,6 +479,9 @@ msi_setup_entry(struct pci_dev *dev, int nvec, struct irq_affinity *affd)
 		goto out;
 
 	pci_read_config_word(dev, dev->msi_cap + PCI_MSI_FLAGS, &control);
+	/* Lies, damned lies, and MSIs */
+	if (dev->dev_flags & PCI_DEV_FLAGS_HAS_MSI_MASKING)
+		control |= PCI_MSI_FLAGS_MASKBIT;
 
 	entry->msi_attrib.is_msix	= 0;
 	entry->msi_attrib.is_64		= !!(control & PCI_MSI_FLAGS_64BIT);
diff --git a/include/linux/pci.h b/include/linux/pci.h
index cd8aa6fce204..152a4d74f87f 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -233,6 +233,8 @@ enum pci_dev_flags {
 	PCI_DEV_FLAGS_NO_FLR_RESET = (__force pci_dev_flags_t) (1 << 10),
 	/* Don't use Relaxed Ordering for TLPs directed at this device */
 	PCI_DEV_FLAGS_NO_RELAXED_ORDERING = (__force pci_dev_flags_t) (1 << 11),
+	/* Device does honor MSI masking despite saying otherwise */
+	PCI_DEV_FLAGS_HAS_MSI_MASKING = (__force pci_dev_flags_t) (1 << 12),
 };
 
 enum pci_irq_reroute_variant {
-- 
2.30.2