Re: [RFC PATCH 2/3] PCI/MSI: Implement irq_mask_nowait() for MSI-x

[Bjorn Helgaas <helgaas@kernel.org>]

[+cc Luigi, cover letter at
https://lore.kernel.org/all/20261013223543.395054-1-kbusch@meta.com]

On Tue, Oct 13, 2026 at 03:35:42PM -0700, Keith Busch wrote:
> 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>

I assume Thomas will review/ack the pci/msi/ parts.

Cc'd Luigi since I know he's interested in interrupt moderation in
general.

> ---
>  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
>