On Mon, Feb 09, 2026 at 09:53:16PM +0900, Koichiro Den wrote:
> pci_epf_alloc_doorbell() currently allocates MSI-backed doorbells using
> the MSI domain returned by of_msi_map_get_device_domain(...,
> DOMAIN_BUS_PLATFORM_MSI). On platforms where such an MSI irq domain is
> not available, EPF drivers cannot provide doorbells to the RC. Even if
> it's available and MSI device domain successfully created, the write
> into the message address via BAR inbound mapping might not work for
> platform-specific reasons (e.g. write into GITS_TRANSLATOR via iATU IB
> mapping does not reach ITS at least on R-Car Gen4 Spider).
>
> Add an "embedded (DMA) doorbell" fallback path that uses EPC-provided
> auxiliary resources to build doorbell address/data pairs backed by a
> platform device MMIO region (e.g. dw-edma) and a shared platform IRQ.
>
> To let EPF drivers request interrupts correctly, extend struct
> pci_epf_doorbell_msg with the doorbell type and required IRQ request
> flags. Update pci-epf-test to handle shared IRQ constraints by using a
> trivial primary handler to wake the threaded handler, and update
> pci-epf-vntb to use the required irq_flags.
>
> Signed-off-by: Koichiro Den <[email protected]>
> ---
> drivers/pci/endpoint/functions/pci-epf-test.c | 29 +++-
> drivers/pci/endpoint/functions/pci-epf-vntb.c | 3 +-
> drivers/pci/endpoint/pci-ep-msi.c | 129 ++++++++++++++++--
> include/linux/pci-epf.h | 17 ++-
> 4 files changed, 160 insertions(+), 18 deletions(-)
>
> diff --git a/drivers/pci/endpoint/functions/pci-epf-test.c
> b/drivers/pci/endpoint/functions/pci-epf-test.c
> index 23034f548c90..2f3b2e6a3e29 100644
> --- a/drivers/pci/endpoint/functions/pci-epf-test.c
> +++ b/drivers/pci/endpoint/functions/pci-epf-test.c
> @@ -711,6 +711,26 @@ static irqreturn_t pci_epf_test_doorbell_handler(int
> irq, void *data)
> return IRQ_HANDLED;
> }
>
> +/*
> + * Embedded doorbell fallback uses a platform IRQ which is already owned by a
> + * platform driver (e.g. dw-edma) and therefore must be requested
> IRQF_SHARED.
> + * We cannot add IRQF_ONESHOT here because shared IRQ handlers must agree on
> + * IRQF_ONESHOT.
> + *
> + * request_threaded_irq() with handler == NULL would be rejected for !ONESHOT
> + * because the default primary handler only wakes the thread and does not
> + * mask/ack the interrupt, which can livelock on level-triggered IRQs.
> + *
> + * In the embedded doorbell fallback, the IRQ owner is responsible for
> + * acknowledging/deasserting the interrupt source in hardirq context before
> the
> + * IRQ line is unmasked. Therefore this driver only needs a trivial primary
> + * handler to wake the threaded handler.
> + */
> +static irqreturn_t pci_epf_test_doorbell_primary(int irq, void *data)
> +{
> + return IRQ_WAKE_THREAD;
> +}
> +
> static void pci_epf_test_doorbell_cleanup(struct pci_epf_test *epf_test)
> {
> struct pci_epf_test_reg *reg = epf_test->reg[epf_test->test_reg_bar];
> @@ -731,6 +751,7 @@ static void pci_epf_test_enable_doorbell(struct
> pci_epf_test *epf_test,
> u32 status = le32_to_cpu(reg->status);
> struct pci_epf *epf = epf_test->epf;
> struct pci_epc *epc = epf->epc;
> + unsigned long irq_flags;
> struct msi_msg *msg;
> enum pci_barno bar;
> size_t offset;
> @@ -745,10 +766,14 @@ static void pci_epf_test_enable_doorbell(struct
> pci_epf_test *epf_test,
> if (bar < BAR_0)
> goto err_doorbell_cleanup;
>
> + irq_flags = epf->db_msg[0].irq_flags;
> + if (!(irq_flags & IRQF_SHARED))
> + irq_flags |= IRQF_ONESHOT;
> epf_test->db_irq_requested = false;
>
> - ret = request_threaded_irq(epf->db_msg[0].virq, NULL,
> - pci_epf_test_doorbell_handler, IRQF_ONESHOT,
> + ret = request_threaded_irq(epf->db_msg[0].virq,
> + pci_epf_test_doorbell_primary,
> + pci_epf_test_doorbell_handler, irq_flags,
> "pci-ep-test-doorbell", epf_test);
> if (ret) {
> dev_err(&epf->dev,
> diff --git a/drivers/pci/endpoint/functions/pci-epf-vntb.c
> b/drivers/pci/endpoint/functions/pci-epf-vntb.c
> index 3ecc5059f92b..d2fd1e194088 100644
> --- a/drivers/pci/endpoint/functions/pci-epf-vntb.c
> +++ b/drivers/pci/endpoint/functions/pci-epf-vntb.c
> @@ -535,7 +535,8 @@ static int epf_ntb_db_bar_init_msi_doorbell(struct
> epf_ntb *ntb,
>
> for (i = 0; i < ntb->db_count; i++) {
> ret = request_irq(epf->db_msg[i].virq, epf_ntb_doorbell_handler,
> - 0, "pci_epf_vntb_db", ntb);
> + epf->db_msg[i].irq_flags, "pci_epf_vntb_db",
> + ntb);
>
> if (ret) {
> dev_err(&epf->dev,
> diff --git a/drivers/pci/endpoint/pci-ep-msi.c
> b/drivers/pci/endpoint/pci-ep-msi.c
> index ad8a81d6ad77..0e93d4789abd 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 +36,84 @@ 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_embedded(struct pci_epf *epf, u16 num_db)
> {
> struct pci_epc *epc = epf->epc;
> - struct device *dev = &epf->dev;
> - struct irq_domain *domain;
> - void *msg;
> - int ret;
> - int i;
> + const struct pci_epc_aux_resource *dma_ctrl = NULL;
> + struct pci_epf_doorbell_msg *msg;
> + int count, ret, i, db;
>
> - /* 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;
> + count = pci_epc_get_aux_resources(epc, epf->func_no, epf->vfunc_no,
> + NULL, 0);
> + if (count == -EOPNOTSUPP || count == 0)
> + return -ENODEV;
> + if (count < 0)
> + return count;
> +
> + struct pci_epc_aux_resource *res __free(kfree) =
> + kcalloc(count, sizeof(*res), GFP_KERNEL);
> + if (!res)
> + return -ENOMEM;
> +
> + ret = pci_epc_get_aux_resources(epc, epf->func_no, epf->vfunc_no,
> + res, count);
> + if (ret == -EOPNOTSUPP || ret == 0)
> + return -ENODEV;
> + if (ret < 0)
> + return ret;
> +
> + count = ret;
> +
> + for (i = 0; i < count; i++) {
> + if (res[i].type == PCI_EPC_AUX_DMA_CTRL_MMIO) {
I suggest use PCI_EPC_EMBEDED_DOORBELL_MMIO directly because some vendor
have really doorbell register space.
below addr is that phys_addr + res[i].u.dma_chan_desc.db_offset. So vendor
can easily change to their doorbell register space in future.
Frank
> + dma_ctrl = &res[i];
> + break;
> + }
> + }
> + if (!dma_ctrl)
> + return -ENODEV;
> +
> + msg = kcalloc(num_db, sizeof(*msg), GFP_KERNEL);
> + if (!msg)
> + return -ENOMEM;
> +
> + for (i = 0, db = 0; i < count && db < num_db; i++) {
> + u64 addr;
> +
> + if (res[i].type != PCI_EPC_AUX_DMA_CHAN_DESC)
> + continue;
> +
> + if (res[i].u.dma_chan_desc.db_offset >= dma_ctrl->size)
> + continue;
> +
> + addr = (u64)dma_ctrl->phys_addr +
> res[i].u.dma_chan_desc.db_offset;
> +
> + msg[db].msg.address_lo = (u32)addr;
> + msg[db].msg.address_hi = (u32)(addr >> 32);
> + msg[db].msg.data = 0;
> + msg[db].virq = res[i].u.dma_chan_desc.irq;
> + msg[db].irq_flags = IRQF_SHARED;
> + msg[db].type = PCI_EPF_DOORBELL_EMBEDDED;
> + db++;
> }
>
> - if (epf->db_msg)
> - return -EBUSY;
> + if (db != num_db) {
> + kfree(msg);
> + return -ENOSPC;
> + }
> +
> + epf->num_db = num_db;
> + epf->db_msg = msg;
> + return 0;
> +}
> +
> +static int pci_epf_alloc_doorbell_msi(struct pci_epf *epf, u16 num_db)
> +{
suggest create patch, which only add helper function
pci_epf_alloc_doorbell_msi().
Then add pci_epf_alloc_doorbell_embedded.
Frank
> + struct pci_epf_doorbell_msg *msg;
> + struct device *dev = &epf->dev;
> + struct pci_epc *epc = epf->epc;
> + struct irq_domain *domain;
> + int ret, i;
>
> domain = of_msi_map_get_device_domain(epc->dev.parent, 0,
> DOMAIN_BUS_PLATFORM_MSI);
> @@ -74,6 +136,11 @@ 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].irq_flags = 0;
> + msg[i].type = PCI_EPF_DOORBELL_MSI;
> + }
> +
> epf->num_db = num_db;
> epf->db_msg = msg;
>
> @@ -90,13 +157,49 @@ 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;
> +
> + if (ret != -ENODEV)
> + return ret;
> +
> + ret = pci_epf_alloc_doorbell_embedded(epf, num_db);
> + if (!ret) {
> + dev_info(dev, "Using embedded (DMA) doorbell fallback\n");
> + 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..e6625198f401 100644
> --- a/include/linux/pci-epf.h
> +++ b/include/linux/pci-epf.h
> @@ -152,14 +152,27 @@ 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.
> */
> struct pci_epf_doorbell_msg {
> struct msi_msg msg;
> int virq;
> + unsigned long irq_flags;
> + enum pci_epf_doorbell_type type;
> };
>
> /**
> --
> 2.51.0
>
