Re: [PATCH v8 6/9] PCI: endpoint: pci-ep-msi: Refactor doorbell allocation for new backends

On Tue, Feb 17, 2026 at 05:05:58PM +0900, Koichiro Den wrote:
> Prepare pci-ep-msi for non-MSI doorbell backends.
>
> Factor MSI doorbell allocation into a helper and extend struct
> pci_epf_doorbell_msg with:
>
>   - irq_flags: required IRQ request flags (e.g. IRQF_SHARED for some
>     backends)
>   - type: doorbell backend type
>   - bar/offset: pre-exposed doorbell target location, if any
>
> Initialize these fields for the existing MSI-backed doorbell
> implementation.
>
> Also add PCI_EPF_DOORBELL_EMBEDDED type, which is to be implemented in a
> follow-up patch.
>
> No functional changes.
>
> Signed-off-by: Koichiro Den <[email protected]>
> ---

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

> Changes since v7:
>   - Switch to designated initializer and rely on implicit
>     zero-initialization.
>
>  drivers/pci/endpoint/pci-ep-msi.c | 54 ++++++++++++++++++++++---------
>  include/linux/pci-epf.h           | 23 +++++++++++--
>  2 files changed, 60 insertions(+), 17 deletions(-)
>
> diff --git a/drivers/pci/endpoint/pci-ep-msi.c b/drivers/pci/endpoint/pci-ep-msi.c
> index ad8a81d6ad77..50badffa9d72 100644
> --- a/drivers/pci/endpoint/pci-ep-msi.c
> +++ b/drivers/pci/endpoint/pci-ep-msi.c
> @@ -8,6 +8,7 @@
>
>  #include <linux/device.h>
>  #include <linux/export.h>
> +#include <linux/interrupt.h>
>  #include <linux/irqdomain.h>
>  #include <linux/module.h>
>  #include <linux/msi.h>
> @@ -35,23 +36,13 @@ static void pci_epf_write_msi_msg(struct msi_desc *desc, struct msi_msg *msg)
>  	pci_epc_put(epc);
>  }
>
> -int pci_epf_alloc_doorbell(struct pci_epf *epf, u16 num_db)
> +static int pci_epf_alloc_doorbell_msi(struct pci_epf *epf, u16 num_db)
>  {
> -	struct pci_epc *epc = epf->epc;
> +	struct pci_epf_doorbell_msg *msg;
>  	struct device *dev = &epf->dev;
> +	struct pci_epc *epc = epf->epc;
>  	struct irq_domain *domain;
> -	void *msg;
> -	int ret;
> -	int i;
> -
> -	/* TODO: Multi-EPF support */
> -	if (list_first_entry_or_null(&epc->pci_epf, struct pci_epf, list) != epf) {
> -		dev_err(dev, "MSI doorbell doesn't support multiple EPF\n");
> -		return -EINVAL;
> -	}
> -
> -	if (epf->db_msg)
> -		return -EBUSY;
> +	int ret, i;
>
>  	domain = of_msi_map_get_device_domain(epc->dev.parent, 0,
>  					      DOMAIN_BUS_PLATFORM_MSI);
> @@ -74,6 +65,12 @@ int pci_epf_alloc_doorbell(struct pci_epf *epf, u16 num_db)
>  	if (!msg)
>  		return -ENOMEM;
>
> +	for (i = 0; i < num_db; i++)
> +		msg[i] = (struct pci_epf_doorbell_msg) {
> +			.type = PCI_EPF_DOORBELL_MSI,
> +			.bar = NO_BAR,
> +		};
> +
>  	epf->num_db = num_db;
>  	epf->db_msg = msg;
>
> @@ -90,13 +87,40 @@ int pci_epf_alloc_doorbell(struct pci_epf *epf, u16 num_db)
>  	for (i = 0; i < num_db; i++)
>  		epf->db_msg[i].virq = msi_get_virq(epc->dev.parent, i);
>
> +	return 0;
> +}
> +
> +int pci_epf_alloc_doorbell(struct pci_epf *epf, u16 num_db)
> +{
> +	struct pci_epc *epc = epf->epc;
> +	struct device *dev = &epf->dev;
> +	int ret;
> +
> +	/* TODO: Multi-EPF support */
> +	if (list_first_entry_or_null(&epc->pci_epf, struct pci_epf, list) != epf) {
> +		dev_err(dev, "Doorbell doesn't support multiple EPF\n");
> +		return -EINVAL;
> +	}
> +
> +	if (epf->db_msg)
> +		return -EBUSY;
> +
> +	ret = pci_epf_alloc_doorbell_msi(epf, num_db);
> +	if (!ret)
> +		return 0;
> +
> +	dev_err(dev, "Failed to allocate doorbell: %d\n", ret);
>  	return ret;
>  }
>  EXPORT_SYMBOL_GPL(pci_epf_alloc_doorbell);
>
>  void pci_epf_free_doorbell(struct pci_epf *epf)
>  {
> -	platform_device_msi_free_irqs_all(epf->epc->dev.parent);
> +	if (!epf->db_msg)
> +		return;
> +
> +	if (epf->db_msg[0].type == PCI_EPF_DOORBELL_MSI)
> +		platform_device_msi_free_irqs_all(epf->epc->dev.parent);
>
>  	kfree(epf->db_msg);
>  	epf->db_msg = NULL;
> diff --git a/include/linux/pci-epf.h b/include/linux/pci-epf.h
> index 7737a7c03260..cd747447a1ea 100644
> --- a/include/linux/pci-epf.h
> +++ b/include/linux/pci-epf.h
> @@ -152,14 +152,33 @@ struct pci_epf_bar {
>  	struct pci_epf_bar_submap	*submap;
>  };
>
> +enum pci_epf_doorbell_type {
> +	PCI_EPF_DOORBELL_MSI = 0,
> +	PCI_EPF_DOORBELL_EMBEDDED,
> +};
> +
>  /**
>   * struct pci_epf_doorbell_msg - represents doorbell message
> - * @msg: MSI message
> - * @virq: IRQ number of this doorbell MSI message
> + * @msg: Doorbell address/data pair to be mapped into BAR space.
> + *       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
> + * @irq_flags: Required flags for request_irq()/request_threaded_irq().
> + *             Callers may OR-in additional flags (e.g. IRQF_ONESHOT).
> + * @type: Doorbell type.
> + * @bar: BAR number where the doorbell target is already exposed to the RC
> + *       (NO_BAR if not)
> + * @offset: offset within @bar for the doorbell target (valid iff
> + *          @bar != NO_BAR)
>   */
>  struct pci_epf_doorbell_msg {
>  	struct msi_msg msg;
>  	int virq;
> +	unsigned long irq_flags;
> +	enum pci_epf_doorbell_type type;
> +	enum pci_barno bar;
> +	resource_size_t offset;
>  };
>
>  /**
> --
> 2.51.0
>