From: Koichiro Den Date: Tue, 14 Apr 2026 14:15:14 +0000 (+0900) Subject: PCI: endpoint: pci-ep-msi: Add embedded doorbell fallback X-Git-Url: http://git.ipfire.org/gitweb/index.cgi?a=commitdiff_plain;h=e4f26243953fd3e87df93786b40293ca3a6a465e;p=thirdparty%2Flinux.git PCI: endpoint: pci-ep-msi: Add embedded doorbell fallback Some endpoint platforms cannot use platform MSI / GIC ITS to implement EP-side doorbells. In those cases, EPF drivers cannot provide an interrupt-driven doorbell and often fall back to polling. Add an "embedded" doorbell backend that uses a controller-integrated doorbell target (e.g. DesignWare integrated eDMA interrupt-emulation doorbell). The backend locates the doorbell register and a corresponding Linux IRQ via the EPC aux-resource API. If the doorbell register is already exposed via a fixed BAR mapping, provide BAR+offset. Otherwise provide the DMA address returned by dma_map_resource() (which may be an IOVA when an IOMMU is enabled) so EPF drivers can map it into BAR space. When MSI doorbell allocation fails with -ENODEV, pci_epf_alloc_doorbell() falls back to this embedded backend. Suggested-by: Manivannan Sadhasivam Signed-off-by: Koichiro Den Signed-off-by: Manivannan Sadhasivam Signed-off-by: Bjorn Helgaas Link: https://patch.msgid.link/20260414141514.1341429-8-den@valinux.co.jp --- diff --git a/drivers/pci/endpoint/pci-ep-msi.c b/drivers/pci/endpoint/pci-ep-msi.c index 85fe46103220..0855c7930abb 100644 --- a/drivers/pci/endpoint/pci-ep-msi.c +++ b/drivers/pci/endpoint/pci-ep-msi.c @@ -6,6 +6,8 @@ * Author: Frank Li */ +#include +#include #include #include #include @@ -36,6 +38,109 @@ static void pci_epf_write_msi_msg(struct msi_desc *desc, struct msi_msg *msg) pci_epc_put(epc); } +static int pci_epf_alloc_doorbell_embedded(struct pci_epf *epf, u16 num_db) +{ + const struct pci_epc_aux_resource *doorbell = NULL; + struct pci_epf_doorbell_msg *msg; + struct pci_epc *epc = epf->epc; + size_t map_size = 0, off = 0; + dma_addr_t iova_base = 0; + phys_addr_t phys_base; + int count, ret, i; + u64 addr; + + count = pci_epc_get_aux_resources_count(epc, epf->func_no, + epf->vfunc_no); + if (count < 0) + return count; + if (!count) + return -ENODEV; + + 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) + return ret; + + /* TODO: Support multiple DOORBELL_MMIO resources per EPC. */ + for (i = 0; i < count; i++) { + if (res[i].type != PCI_EPC_AUX_DOORBELL_MMIO) + continue; + + doorbell = &res[i]; + break; + } + if (!doorbell) + return -ENODEV; + addr = doorbell->phys_addr; + if (!IS_ALIGNED(addr, sizeof(u32))) + return -EINVAL; + + /* + * Reuse the pre-exposed BAR window if available. Otherwise map the MMIO + * doorbell resource here. Any required IOMMU mapping is handled + * internally, matching the MSI doorbell semantics. + */ + if (doorbell->bar == NO_BAR) { + phys_base = addr & PAGE_MASK; + off = addr - phys_base; + map_size = PAGE_ALIGN(off + sizeof(u32)); + + iova_base = dma_map_resource(epc->dev.parent, phys_base, + map_size, DMA_FROM_DEVICE, 0); + if (dma_mapping_error(epc->dev.parent, iova_base)) + return -EIO; + + addr = iova_base + off; + } + + msg = kcalloc(num_db, sizeof(*msg), GFP_KERNEL); + if (!msg) { + ret = -ENOMEM; + goto err_unmap; + } + + /* + * Embedded doorbell backends (e.g. DesignWare eDMA interrupt emulation) + * typically provide a single IRQ and do not offer per-doorbell + * distinguishable address/data pairs. The EPC aux resource therefore + * exposes one DOORBELL_MMIO entry (u.db_mmio.irq). + * + * 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. + */ + for (i = 0; i < num_db; i++) + msg[i] = (struct pci_epf_doorbell_msg) { + .msg.address_lo = (u32)addr, + .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 : + doorbell->bar_offset, + .iova_base = iova_base, + .iova_size = map_size, + }; + + epf->num_db = num_db; + epf->db_msg = msg; + return 0; + +err_unmap: + if (map_size) + dma_unmap_resource(epc->dev.parent, iova_base, map_size, + DMA_FROM_DEVICE, 0); + return ret; +} + static int pci_epf_alloc_doorbell_msi(struct pci_epf *epf, u16 num_db) { struct pci_epf_doorbell_msg *msg; @@ -109,18 +214,38 @@ int pci_epf_alloc_doorbell(struct pci_epf *epf, u16 num_db) if (!ret) return 0; - dev_err(dev, "Failed to allocate doorbell: %d\n", ret); - return ret; + /* + * Fall back to embedded doorbell only when platform MSI is unavailable + * for this EPC. + */ + if (ret != -ENODEV) + return ret; + + ret = pci_epf_alloc_doorbell_embedded(epf, num_db); + if (ret) { + dev_err(dev, "Failed to allocate doorbell: %d\n", ret); + return ret; + } + + dev_info(dev, "Using embedded (DMA) doorbell fallback\n"); + return 0; } EXPORT_SYMBOL_GPL(pci_epf_alloc_doorbell); void pci_epf_free_doorbell(struct pci_epf *epf) { + struct pci_epf_doorbell_msg *msg0; + struct pci_epc *epc = epf->epc; + if (!epf->db_msg) return; - if (epf->db_msg[0].type == PCI_EPF_DOORBELL_MSI) + msg0 = &epf->db_msg[0]; + if (msg0->type == PCI_EPF_DOORBELL_MSI) platform_device_msi_free_irqs_all(epf->epc->dev.parent); + else if (msg0->type == PCI_EPF_DOORBELL_EMBEDDED && msg0->iova_size) + dma_unmap_resource(epc->dev.parent, msg0->iova_base, + msg0->iova_size, DMA_FROM_DEVICE, 0); kfree(epf->db_msg); epf->db_msg = NULL; diff --git a/include/linux/pci-epf.h b/include/linux/pci-epf.h index cd747447a1ea..8a6c64a35890 100644 --- a/include/linux/pci-epf.h +++ b/include/linux/pci-epf.h @@ -171,6 +171,12 @@ enum pci_epf_doorbell_type { * (NO_BAR if not) * @offset: offset within @bar for the doorbell target (valid iff * @bar != NO_BAR) + * @iova_base: Internal: base DMA address returned by dma_map_resource() for the + * embedded doorbell MMIO window (used only for unmapping). Valid + * when @type is PCI_EPF_DOORBELL_EMBEDDED and @iova_size is + * non-zero. + * @iova_size: Internal: size of the dma_map_resource() mapping at @iova_base. + * Zero when no mapping was created (e.g. pre-exposed fixed BAR). */ struct pci_epf_doorbell_msg { struct msi_msg msg; @@ -179,6 +185,8 @@ struct pci_epf_doorbell_msg { enum pci_epf_doorbell_type type; enum pci_barno bar; resource_size_t offset; + dma_addr_t iova_base; + size_t iova_size; }; /**