[PATCH v3 2/2] PCI/MSI: Implement irq_mask_noflush() for MSI-X

[Keith Busch <kbusch@meta.com>]

From: Keith Busch <kbusch@kernel.org>

Skip the read-back that flushes the MSI-X mask write. Parent domains
that mask on behalf of PCI/MSI keep using their own irq_mask().

Suggested-by: Thomas Gleixner <tglx@kernel.org>
Signed-off-by: Keith Busch <kbusch@kernel.org>
---
 drivers/irqchip/irq-msi-lib.c |  1 +
 drivers/pci/msi/irqdomain.c   |  6 ++++++
 drivers/pci/msi/msi.h         | 10 ++++++++--
 3 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/drivers/irqchip/irq-msi-lib.c b/drivers/irqchip/irq-msi-lib.c
index 45e0ed3134ce1..97bc95d592122 100644
--- a/drivers/irqchip/irq-msi-lib.c
+++ b/drivers/irqchip/irq-msi-lib.c
@@ -126,6 +126,7 @@ bool msi_lib_init_dev_msi_info(struct device *dev, struct irq_domain *domain,
 	 */
 	if (info->flags & MSI_FLAG_PCI_MSI_MASK_PARENT) {
 		chip->irq_mask		= irq_chip_mask_parent;
+		chip->irq_mask_noflush	= NULL;
 		chip->irq_unmask	= irq_chip_unmask_parent;
 	}
 
diff --git a/drivers/pci/msi/irqdomain.c b/drivers/pci/msi/irqdomain.c
index 6e65f0f44112e..2b9a5a0c305fb 100644
--- a/drivers/pci/msi/irqdomain.c
+++ b/drivers/pci/msi/irqdomain.c
@@ -162,6 +162,11 @@ static void pci_irq_mask_msix(struct irq_data *data)
 	pci_msix_mask(irq_data_get_msi_desc(data));
 }
 
+static void pci_irq_mask_noflush_msix(struct irq_data *data)
+{
+	pci_msix_mask_noflush(irq_data_get_msi_desc(data));
+}
+
 static void pci_irq_unmask_msix(struct irq_data *data)
 {
 	pci_msix_unmask(irq_data_get_msi_desc(data));
@@ -182,6 +187,7 @@ static const struct msi_domain_template pci_msix_template = {
 		.irq_startup		= pci_irq_startup_msix,
 		.irq_shutdown		= pci_irq_shutdown_msix,
 		.irq_mask		= pci_irq_mask_msix,
+		.irq_mask_noflush	= pci_irq_mask_noflush_msix,
 		.irq_unmask		= pci_irq_unmask_msix,
 		.irq_write_msi_msg	= pci_msi_domain_write_msg,
 		.flags			= IRQCHIP_ONESHOT_SAFE,
diff --git a/drivers/pci/msi/msi.h b/drivers/pci/msi/msi.h
index f987cf897264e..c40d24e5ca901 100644
--- a/drivers/pci/msi/msi.h
+++ b/drivers/pci/msi/msi.h
@@ -44,14 +44,20 @@ static inline void pci_msix_write_vector_ctrl(struct msi_desc *desc, u32 ctrl)
 		writel(ctrl, desc_addr + PCI_MSIX_ENTRY_VECTOR_CTRL);
 }
 
-static inline void pci_msix_mask(struct msi_desc *desc)
+/* Posted write only: the device may still send an interrupt after return */
+static inline void pci_msix_mask_noflush(struct msi_desc *desc)
 {
 	desc->pci.msix_ctrl |= PCI_MSIX_ENTRY_CTRL_MASKBIT;
+	pci_msix_write_vector_ctrl(desc, desc->pci.msix_ctrl);
+}
+
+static inline void pci_msix_mask(struct msi_desc *desc)
+{
+	pci_msix_mask_noflush(desc);
 
 	if (pci_channel_offline(msi_desc_to_pci_dev(desc)))
 		return;
 
-	pci_msix_write_vector_ctrl(desc, desc->pci.msix_ctrl);
 	/* Flush write to device */
 	readl(desc->pci.mask_base);
 }
-- 
2.52.0