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PCI: endpoint: pci-ep-msi: Add embedded doorbell fallback

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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 <mani@kernel.org>
Signed-off-by: Koichiro Den <den@valinux.co.jp>
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Link: https://patch.msgid.link/20260414141514.1341429-8-den@valinux.co.jp
This commit is contained in:
Koichiro Den
2026-04-14 23:15:14 +09:00
committed by Bjorn Helgaas
parent 8fda2dd209
commit e4f2624395
2 changed files with 136 additions and 3 deletions
Download Patch File Download Diff File Expand all files Collapse all files

131
drivers/pci/endpoint/pci-ep-msi.c
View File

@@ -6,6 +6,8 @@
* Author: Frank Li <Frank.Li@nxp.com>
*/
#include <linux/align.h>
#include <linux/cleanup.h>
#include <linux/device.h>
#include <linux/export.h>
#include <linux/interrupt.h>
@@ -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;

8
include/linux/pci-epf.h
View File

@@ -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;
};
/**