[RFC PATCH 2/3] PCI/MSI: Implement irq_mask_nowait() 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 continue using their own irq_mask().

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         | 8 +++++++-
 3 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/drivers/irqchip/irq-msi-lib.c b/drivers/irqchip/irq-msi-lib.c
index 45e0ed3134ce1..bff622b4839aa 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_nowait	= NULL;
 		chip->irq_unmask	= irq_chip_unmask_parent;
 	}
 
diff --git a/drivers/pci/msi/irqdomain.c b/drivers/pci/msi/irqdomain.c
index 6e65f0f44112e..92a53c2772659 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_nowait_msix(struct irq_data *data)
+{
+	pci_msix_mask_nowait(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_nowait	= pci_irq_mask_nowait_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 0b420b319f50f..337ff9d9da0ed 100644
--- a/drivers/pci/msi/msi.h
+++ b/drivers/pci/msi/msi.h
@@ -40,10 +40,16 @@ 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_nowait(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_nowait(desc);
 	/* Flush write to device */
 	readl(desc->pci.mask_base);
 }
-- 
2.52.0