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Message-ID: <aYY_Ghig9wvnp8Wg@lizhi-Precision-Tower-5810>
Date: Fri, 6 Feb 2026 14:20:58 -0500
From: Frank Li <Frank.li@....com>
To: Koichiro Den <den@...inux.co.jp>
Cc: vkoul@...nel.org, mani@...nel.org, jingoohan1@...il.com,
lpieralisi@...nel.org, kwilczynski@...nel.org, robh@...nel.org,
bhelgaas@...gle.com, dmaengine@...r.kernel.org,
linux-pci@...r.kernel.org, linux-kselftest@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 7/9] PCI: endpoint: pci-epf-test: Add embedded
doorbell variant
On Sat, Feb 07, 2026 at 02:26:44AM +0900, Koichiro Den wrote:
> Extend pci-epf-test with an "embedded doorbell" variant that does not
> rely on the EPC doorbell/MSI mechanism.
>
> When the host sets FLAG_DB_EMBEDDED, query EPC remote resources to
> locate the embedded DMA MMIO window and a per-channel
> interrupt-emulation doorbell register offset. Map the MMIO window into a
> free BAR and return BAR+offset to the host as the doorbell target.
>
> Handle the resulting shared IRQ by deferring completion signalling to a
> work item, then update the test status and raise the completion IRQ back
> to the host.
>
> The existing MSI doorbell remains the default when FLAG_DB_EMBEDDED is
> not set.
>
> Signed-off-by: Koichiro Den <den@...inux.co.jp>
> ---
Can you change pci_epf_alloc_doorbell() directly? Let it fall back to
edma implement.
Frank
> drivers/pci/endpoint/functions/pci-epf-test.c | 193 +++++++++++++++++-
> 1 file changed, 185 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/pci/endpoint/functions/pci-epf-test.c b/drivers/pci/endpoint/functions/pci-epf-test.c
> index 6952ee418622..5871da8cbddf 100644
> --- a/drivers/pci/endpoint/functions/pci-epf-test.c
> +++ b/drivers/pci/endpoint/functions/pci-epf-test.c
> @@ -6,6 +6,7 @@
> * Author: Kishon Vijay Abraham I <kishon@...com>
> */
>
> +#include <linux/bitops.h>
> #include <linux/crc32.h>
> #include <linux/delay.h>
> #include <linux/dmaengine.h>
> @@ -56,6 +57,7 @@
> #define STATUS_BAR_SUBRANGE_CLEAR_FAIL BIT(17)
>
> #define FLAG_USE_DMA BIT(0)
> +#define FLAG_DB_EMBEDDED BIT(1)
>
> #define TIMER_RESOLUTION 1
>
> @@ -69,6 +71,12 @@
>
> static struct workqueue_struct *kpcitest_workqueue;
>
> +enum pci_epf_test_doorbell_variant {
> + PCI_EPF_TEST_DB_NONE = 0,
> + PCI_EPF_TEST_DB_MSI,
> + PCI_EPF_TEST_DB_EMBEDDED,
> +};
> +
> struct pci_epf_test {
> void *reg[PCI_STD_NUM_BARS];
> struct pci_epf *epf;
> @@ -85,7 +93,11 @@ struct pci_epf_test {
> bool dma_supported;
> bool dma_private;
> const struct pci_epc_features *epc_features;
> + enum pci_epf_test_doorbell_variant db_variant;
> struct pci_epf_bar db_bar;
> + int db_irq;
> + unsigned long db_irq_pending;
> + struct work_struct db_work;
> size_t bar_size[PCI_STD_NUM_BARS];
> };
>
> @@ -696,7 +708,7 @@ static void pci_epf_test_raise_irq(struct pci_epf_test *epf_test,
> }
> }
>
> -static irqreturn_t pci_epf_test_doorbell_handler(int irq, void *data)
> +static irqreturn_t pci_epf_test_doorbell_msi_handler(int irq, void *data)
> {
> struct pci_epf_test *epf_test = data;
> enum pci_barno test_reg_bar = epf_test->test_reg_bar;
> @@ -710,19 +722,58 @@ static irqreturn_t pci_epf_test_doorbell_handler(int irq, void *data)
> return IRQ_HANDLED;
> }
>
> +static void pci_epf_test_doorbell_embedded_work(struct work_struct *work)
> +{
> + struct pci_epf_test *epf_test =
> + container_of(work, struct pci_epf_test, db_work);
> + enum pci_barno test_reg_bar = epf_test->test_reg_bar;
> + struct pci_epf_test_reg *reg = epf_test->reg[test_reg_bar];
> + u32 status = le32_to_cpu(reg->status);
> +
> + status |= STATUS_DOORBELL_SUCCESS;
> + reg->status = cpu_to_le32(status);
> + pci_epf_test_raise_irq(epf_test, reg);
> +
> + clear_bit(0, &epf_test->db_irq_pending);
> +}
> +
> +static irqreturn_t pci_epf_test_doorbell_embedded_irq_handler(int irq, void *data)
> +{
> + struct pci_epf_test *epf_test = data;
> +
> + if (READ_ONCE(epf_test->db_variant) != PCI_EPF_TEST_DB_EMBEDDED)
> + return IRQ_NONE;
> +
> + if (test_and_set_bit(0, &epf_test->db_irq_pending))
> + return IRQ_HANDLED;
> +
> + queue_work(kpcitest_workqueue, &epf_test->db_work);
> + return IRQ_HANDLED;
> +}
> +
> 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];
> struct pci_epf *epf = epf_test->epf;
>
> - free_irq(epf->db_msg[0].virq, epf_test);
> - reg->doorbell_bar = cpu_to_le32(NO_BAR);
> + if (epf_test->db_irq) {
> + free_irq(epf_test->db_irq, epf_test);
> + epf_test->db_irq = 0;
> + }
> +
> + if (epf_test->db_variant == PCI_EPF_TEST_DB_EMBEDDED) {
> + cancel_work_sync(&epf_test->db_work);
> + clear_bit(0, &epf_test->db_irq_pending);
> + } else if (epf_test->db_variant == PCI_EPF_TEST_DB_MSI) {
> + pci_epf_free_doorbell(epf);
> + }
>
> - pci_epf_free_doorbell(epf);
> + reg->doorbell_bar = cpu_to_le32(NO_BAR);
> + epf_test->db_variant = PCI_EPF_TEST_DB_NONE;
> }
>
> -static void pci_epf_test_enable_doorbell(struct pci_epf_test *epf_test,
> - struct pci_epf_test_reg *reg)
> +static void pci_epf_test_enable_doorbell_msi(struct pci_epf_test *epf_test,
> + struct pci_epf_test_reg *reg)
> {
> u32 status = le32_to_cpu(reg->status);
> struct pci_epf *epf = epf_test->epf;
> @@ -736,20 +787,23 @@ static void pci_epf_test_enable_doorbell(struct pci_epf_test *epf_test,
> if (ret)
> goto set_status_err;
>
> + epf_test->db_variant = PCI_EPF_TEST_DB_MSI;
> msg = &epf->db_msg[0].msg;
> bar = pci_epc_get_next_free_bar(epf_test->epc_features, epf_test->test_reg_bar + 1);
> if (bar < BAR_0)
> goto err_doorbell_cleanup;
>
> ret = request_threaded_irq(epf->db_msg[0].virq, NULL,
> - pci_epf_test_doorbell_handler, IRQF_ONESHOT,
> - "pci-ep-test-doorbell", epf_test);
> + pci_epf_test_doorbell_msi_handler,
> + IRQF_ONESHOT, "pci-ep-test-doorbell",
> + epf_test);
> if (ret) {
> dev_err(&epf->dev,
> "Failed to request doorbell IRQ: %d\n",
> epf->db_msg[0].virq);
> goto err_doorbell_cleanup;
> }
> + epf_test->db_irq = epf->db_msg[0].virq;
>
> reg->doorbell_data = cpu_to_le32(msg->data);
> reg->doorbell_bar = cpu_to_le32(bar);
> @@ -782,6 +836,125 @@ static void pci_epf_test_enable_doorbell(struct pci_epf_test *epf_test,
> reg->status = cpu_to_le32(status);
> }
>
> +static void pci_epf_test_enable_doorbell_embedded(struct pci_epf_test *epf_test,
> + struct pci_epf_test_reg *reg)
> +{
> + struct pci_epc_remote_resource *dma_ctrl = NULL, *chan0 = NULL;
> + const char *irq_name = "pci-ep-test-doorbell-embedded";
> + u32 status = le32_to_cpu(reg->status);
> + struct pci_epf *epf = epf_test->epf;
> + struct pci_epc *epc = epf->epc;
> + struct device *dev = &epf->dev;
> + enum pci_barno bar;
> + size_t align_off;
> + unsigned int i;
> + int cnt, ret;
> + u32 db_off;
> +
> + cnt = pci_epc_get_remote_resources(epc, epf->func_no, epf->vfunc_no,
> + NULL, 0);
> + if (cnt <= 0) {
> + dev_err(dev, "No remote resources available for embedded doorbell\n");
> + goto set_status_err;
> + }
> +
> + struct pci_epc_remote_resource *resources __free(kfree) =
> + kcalloc(cnt, sizeof(*resources), GFP_KERNEL);
> + if (!resources)
> + goto set_status_err;
> +
> + ret = pci_epc_get_remote_resources(epc, epf->func_no, epf->vfunc_no,
> + resources, cnt);
> + if (ret < 0) {
> + dev_err(dev, "Failed to get remote resources: %d\n", ret);
> + goto set_status_err;
> + }
> + cnt = ret;
> +
> + for (i = 0; i < cnt; i++) {
> + if (resources[i].type == PCI_EPC_RR_DMA_CTRL_MMIO)
> + dma_ctrl = &resources[i];
> + else if (resources[i].type == PCI_EPC_RR_DMA_CHAN_DESC &&
> + !chan0)
> + chan0 = &resources[i];
> + }
> +
> + if (!dma_ctrl || !chan0) {
> + dev_err(dev, "Missing DMA ctrl MMIO or channel #0 info\n");
> + goto set_status_err;
> + }
> +
> + bar = pci_epc_get_next_free_bar(epf_test->epc_features,
> + epf_test->test_reg_bar + 1);
> + if (bar < BAR_0) {
> + dev_err(dev, "No free BAR for embedded doorbell\n");
> + goto set_status_err;
> + }
> +
> + ret = pci_epf_align_inbound_addr(epf, bar, dma_ctrl->phys_addr,
> + &epf_test->db_bar.phys_addr,
> + &align_off);
> + if (ret)
> + goto set_status_err;
> +
> + db_off = chan0->u.dma_chan_desc.db_offset;
> + if (db_off >= dma_ctrl->size ||
> + align_off + db_off >= epf->bar[bar].size) {
> + dev_err(dev, "BAR%d too small for embedded doorbell (off %#zx + %#x)\n",
> + bar, align_off, db_off);
> + goto set_status_err;
> + }
> +
> + epf_test->db_variant = PCI_EPF_TEST_DB_EMBEDDED;
> +
> + ret = request_irq(chan0->u.dma_chan_desc.irq,
> + pci_epf_test_doorbell_embedded_irq_handler,
> + IRQF_SHARED, irq_name, epf_test);
> + if (ret) {
> + dev_err(dev, "Failed to request embedded doorbell IRQ: %d\n",
> + chan0->u.dma_chan_desc.irq);
> + goto err_cleanup;
> + }
> + epf_test->db_irq = chan0->u.dma_chan_desc.irq;
> +
> + reg->doorbell_data = cpu_to_le32(0);
> + reg->doorbell_bar = cpu_to_le32(bar);
> + reg->doorbell_offset = cpu_to_le32(align_off + db_off);
> +
> + epf_test->db_bar.barno = bar;
> + epf_test->db_bar.size = epf->bar[bar].size;
> + epf_test->db_bar.flags = epf->bar[bar].flags;
> +
> + ret = pci_epc_set_bar(epc, epf->func_no, epf->vfunc_no, &epf_test->db_bar);
> + if (ret)
> + goto err_cleanup;
> +
> + status |= STATUS_DOORBELL_ENABLE_SUCCESS;
> + reg->status = cpu_to_le32(status);
> + return;
> +
> +err_cleanup:
> + pci_epf_test_doorbell_cleanup(epf_test);
> +set_status_err:
> + status |= STATUS_DOORBELL_ENABLE_FAIL;
> + reg->status = cpu_to_le32(status);
> +}
> +
> +static void pci_epf_test_enable_doorbell(struct pci_epf_test *epf_test,
> + struct pci_epf_test_reg *reg)
> +{
> + u32 flags = le32_to_cpu(reg->flags);
> +
> + /* If already enabled, drop previous setup first. */
> + if (epf_test->db_variant != PCI_EPF_TEST_DB_NONE)
> + pci_epf_test_doorbell_cleanup(epf_test);
> +
> + if (flags & FLAG_DB_EMBEDDED)
> + pci_epf_test_enable_doorbell_embedded(epf_test, reg);
> + else
> + pci_epf_test_enable_doorbell_msi(epf_test, reg);
> +}
> +
> static void pci_epf_test_disable_doorbell(struct pci_epf_test *epf_test,
> struct pci_epf_test_reg *reg)
> {
> @@ -1309,6 +1482,9 @@ static void pci_epf_test_unbind(struct pci_epf *epf)
>
> cancel_delayed_work_sync(&epf_test->cmd_handler);
> if (epc->init_complete) {
> + /* In case userspace never disabled doorbell explicitly. */
> + if (epf_test->db_variant != PCI_EPF_TEST_DB_NONE)
> + pci_epf_test_doorbell_cleanup(epf_test);
> pci_epf_test_clean_dma_chan(epf_test);
> pci_epf_test_clear_bar(epf);
> }
> @@ -1427,6 +1603,7 @@ static int pci_epf_test_probe(struct pci_epf *epf,
> epf_test->bar_size[bar] = default_bar_size[bar];
>
> INIT_DELAYED_WORK(&epf_test->cmd_handler, pci_epf_test_cmd_handler);
> + INIT_WORK(&epf_test->db_work, pci_epf_test_doorbell_embedded_work);
>
> epf->event_ops = &pci_epf_test_event_ops;
>
> --
> 2.51.0
>
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