Re: [PATCH 2/3] PCI: endpoint: pci-ep-msi: Make embedded doorbell IRQ exclusive

On Wed, Jul 29, 2026 at 02:23:05AM +0900, Koichiro Den wrote:
> Embedded doorbells may use the same virq for several messages. This does
> not mean the IRQ itself should be shared. Consumers only need to request
> each distinct virq once, as vNTB and pci-epf-test already do.
>
> IRQF_SHARED would let different EPFs register handlers for the same IRQ.
> The embedded doorbell interface cannot tell which EPF a write targets,
> so every handler would handle it.
>
> Only the first EPF can allocate doorbells today, so this cannot happen
> yet. Drop IRQF_SHARED before extending the embedded backend to non-first
> EPFs. A second request for the same IRQ will then fail with -EBUSY
> instead of attaching another handler.
>
> Signed-off-by: Koichiro Den <[email protected]>
> ---

Reviewed-by: Frank Li <[email protected]>

>  drivers/pci/endpoint/pci-ep-msi.c | 9 +++++----
>  include/linux/pci-epf.h           | 3 ++-
>  2 files changed, 7 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/pci/endpoint/pci-ep-msi.c b/drivers/pci/endpoint/pci-ep-msi.c
> index 0855c7930abb..a123a189b4e6 100644
> --- a/drivers/pci/endpoint/pci-ep-msi.c
> +++ b/drivers/pci/endpoint/pci-ep-msi.c
> @@ -10,7 +10,6 @@
>  #include <linux/cleanup.h>
>  #include <linux/device.h>
>  #include <linux/export.h>
> -#include <linux/interrupt.h>
>  #include <linux/irqdomain.h>
>  #include <linux/module.h>
>  #include <linux/msi.h>
> @@ -112,8 +111,11 @@ static int pci_epf_alloc_doorbell_embedded(struct pci_epf *epf, u16 num_db)
>  	 *
>  	 * Still, pci_epf_alloc_doorbell() allows requesting multiple doorbells.
>  	 * For such backends we replicate the same address/data for each entry
> -	 * and mark the IRQ as shared (IRQF_SHARED). Consumers must treat them
> -	 * as equivalent "kick" doorbells.
> +	 * as equivalent "kick" doorbells. Consumers must request each distinct
> +	 * IRQ only once.
> +	 *
> +	 * Keep the IRQ exclusive because the source cannot identify which EPF
> +	 * rang the doorbell.
>  	 */
>  	for (i = 0; i < num_db; i++)
>  		msg[i] = (struct pci_epf_doorbell_msg) {
> @@ -121,7 +123,6 @@ static int pci_epf_alloc_doorbell_embedded(struct pci_epf *epf, u16 num_db)
>  			.msg.address_hi = (u32)(addr >> 32),
>  			.msg.data = doorbell->u.db_mmio.data,
>  			.virq = doorbell->u.db_mmio.irq,
> -			.irq_flags = IRQF_SHARED,
>  			.type = PCI_EPF_DOORBELL_EMBEDDED,
>  			.bar = doorbell->bar,
>  			.offset = (doorbell->bar == NO_BAR) ? 0 :
> diff --git a/include/linux/pci-epf.h b/include/linux/pci-epf.h
> index 8a6c64a35890..e5b9a79beb93 100644
> --- a/include/linux/pci-epf.h
> +++ b/include/linux/pci-epf.h
> @@ -163,7 +163,8 @@ enum pci_epf_doorbell_type {
>   *       For MSI-backed doorbells this is the MSI message, while for
>   *       "embedded" doorbells this represents an MMIO write that asserts
>   *       an interrupt on the EP side.
> - * @virq: IRQ number of this doorbell message
> + * @virq: IRQ number of this doorbell message. Multiple messages may use the
> + *        same IRQ; consumers must request each distinct IRQ only once.
>   * @irq_flags: Required flags for request_irq()/request_threaded_irq().
>   *             Callers may OR-in additional flags (e.g. IRQF_ONESHOT).
>   * @type: Doorbell type.
> --
> 2.51.0
>