Re: [PATCH 3/3] PCI: endpoint: pci-epf-vntb: Honor MSI-X selection

[Frank Li]

On Fri, Aug 28, 2026 at 03:20:12AM +0900, Koichiro Den wrote:
> ntb_hw_epf tries MSI-X first and falls back to MSI. It reports the
> result in COMMAND_CONFIGURE_DOORBELL. pci-epf-vntb ignores MSIX_ENABLE,
> configures only MSI, and always raises peer doorbells with PCI_IRQ_MSI.
> When MSI-X is selected, the host does not program MSI, so raising it can
> issue a write to an invalid address. This was observed with an IOMMU
> enabled on the RC.
>
> Configure MSI-X when supported and use the selected type for peer
> doorbells. Use the hardware-owned layout when available. Otherwise
> allocate an EPF-owned Table and PBA in the config BAR. Configure db_count
> entries to cover the link event, the reserved slot, and the doorbell
> slots.
>
> Fixes: e35f56bb0330 ("PCI: endpoint: Support NTB transfer between RC and EP")
> Signed-off-by: Koichiro Den <den@xxxxxxxxxxxxx>
> ---

Reviewed-by: Frank Li <Frank.Li@xxxxxxx>

>  drivers/pci/endpoint/functions/pci-epf-vntb.c | 67 ++++++++++++++-----
>  1 file changed, 51 insertions(+), 16 deletions(-)
>
> diff --git a/drivers/pci/endpoint/functions/pci-epf-vntb.c b/drivers/pci/endpoint/functions/pci-epf-vntb.c
> index c3caec927d74..d9622a5d4710 100644
> --- a/drivers/pci/endpoint/functions/pci-epf-vntb.c
> +++ b/drivers/pci/endpoint/functions/pci-epf-vntb.c
> @@ -148,6 +148,7 @@ struct epf_ntb {
>  	u16 vntb_vid;
>
>  	bool linkup;
> +	bool peer_msix;
>
>  	/*
>  	 * True when doorbells are interrupt-driven (MSI or embedded), false
> @@ -155,6 +156,7 @@ struct epf_ntb {
>  	 */
>  	bool msi_doorbell;
>  	u32 spad_size;
> +	struct pci_epc_msix_layout msix_layout;
>
>  	enum pci_barno epf_ntb_bar[VNTB_BAR_NUM];
>
> @@ -303,6 +305,7 @@ static void epf_ntb_cmd_handler(struct work_struct *work)
>
>  	switch (command) {
>  	case COMMAND_CONFIGURE_DOORBELL:
> +		WRITE_ONCE(ntb->peer_msix, argument & MSIX_ENABLE);
>  		ctrl->command_status = COMMAND_STATUS_OK;
>  		break;
>  	case COMMAND_TEARDOWN_DOORBELL:
> @@ -439,9 +442,9 @@ static void epf_ntb_config_spad_bar_free(struct epf_ntb *ntb)
>   *   region
>   * @ntb: NTB device that facilitates communication between HOST and VHOST
>   *
> - * Allocate the Local Memory mentioned in the above diagram. The size of
> - * CONFIG REGION is sizeof(struct epf_ntb_ctrl) and size of SCRATCHPAD REGION
> - * is obtained from "spad-count" configfs entry.
> + * Allocate the control and scratchpad regions described in the above diagram.
> + * If the EPC does not provide a hardware-owned MSI-X table and PBA, allocate
> + * space for them between the control and scratchpad regions.
>   *
>   * Returns: Zero for success, or an error code in case of failure
>   */
> @@ -454,7 +457,7 @@ static int epf_ntb_config_spad_bar_alloc(struct epf_ntb *ntb)
>  	struct device *dev = &epf->dev;
>  	u32 spad_count;
>  	void *base;
> -	int i;
> +	int i, ret;
>  	const struct pci_epc_features *epc_features = pci_epc_get_features(epf->epc,
>  								epf->func_no,
>  								epf->vfunc_no);
> @@ -462,6 +465,29 @@ static int epf_ntb_config_spad_bar_alloc(struct epf_ntb *ntb)
>  	spad_count = ntb->spad_count;
>
>  	ctrl_size = ALIGN(sizeof(struct epf_ntb_ctrl), sizeof(u32));
> +	if (epc_features->msix_capable) {
> +		ret = pci_epc_get_hw_msix_layout(epc_features,
> +						 &ntb->msix_layout);
> +		if (ret && ret != -ENOENT) {
> +			dev_err(dev, "Invalid hardware-owned MSI-X layout\n");
> +			return ret;
> +		}
> +
> +		if (ret == -ENOENT) {
> +			ntb->msix_layout.table_bar = barno;
> +			ntb->msix_layout.table_offset = ALIGN(ctrl_size, 8);
> +			ntb->msix_layout.table_size =
> +				ntb->db_count * PCI_MSIX_ENTRY_SIZE;
> +			ntb->msix_layout.pba_bar = barno;
> +			ntb->msix_layout.pba_offset =
> +				ntb->msix_layout.table_offset +
> +				ntb->msix_layout.table_size;
> +			ntb->msix_layout.pba_size =
> +				BITS_TO_U64(ntb->db_count) * sizeof(u64);
> +			ctrl_size = ntb->msix_layout.pba_offset +
> +				    ntb->msix_layout.pba_size;
> +		}
> +	}
>  	spad_size = 2 * spad_count * sizeof(u32);
>
>  	base = pci_epf_alloc_space(epf, ctrl_size + spad_size,
> @@ -502,6 +528,7 @@ static int epf_ntb_config_spad_bar_alloc(struct epf_ntb *ntb)
>  static int epf_ntb_configure_interrupt(struct epf_ntb *ntb)
>  {
>  	const struct pci_epc_features *epc_features;
> +	struct pci_epf *epf = ntb->epf;
>  	struct device *dev;
>  	int ret;
>
> @@ -521,16 +548,22 @@ static int epf_ntb_configure_interrupt(struct epf_ntb *ntb)
>  	}
>
>  	if (epc_features->msi_capable) {
> -		ret = pci_epc_set_msi(ntb->epf->epc,
> -				      ntb->epf->func_no,
> -				      ntb->epf->vfunc_no,
> -				      16);
> +		ret = pci_epc_set_msi(epf->epc, epf->func_no, epf->vfunc_no, 16);
>  		if (ret) {
>  			dev_err(dev, "MSI configuration failed\n");
>  			return ret;
>  		}
>  	}
>
> +	if (epc_features->msix_capable) {
> +		ret = pci_epc_set_msix(epf->epc, epf->func_no, epf->vfunc_no,
> +				       ntb->db_count, &ntb->msix_layout);
> +		if (ret) {
> +			dev_err(dev, "MSI-X configuration failed\n");
> +			return ret;
> +		}
> +	}
> +
>  	return 0;
>  }
>
> @@ -1512,6 +1545,7 @@ static void vntb_epf_peer_db_work(struct work_struct *work)
>  	struct epf_ntb *ntb = container_of(work, struct epf_ntb, peer_db_work);
>  	struct pci_epf *epf = ntb->epf;
>  	unsigned int budget = VNTB_PEER_DB_WORK_BUDGET;
> +	unsigned int irq_type;
>  	u8 func_no, vfunc_no;
>  	unsigned int db_bit;
>  	u32 interrupt_num;
> @@ -1523,6 +1557,7 @@ static void vntb_epf_peer_db_work(struct work_struct *work)
>
>  	func_no = epf->func_no;
>  	vfunc_no = epf->vfunc_no;
> +	irq_type = READ_ONCE(ntb->peer_msix) ? PCI_IRQ_MSIX : PCI_IRQ_MSI;
>
>  	/*
>  	 * Drain doorbells from peer_db_pending in snapshots (atomic64_xchg()).
> @@ -1536,16 +1571,16 @@ static void vntb_epf_peer_db_work(struct work_struct *work)
>
>  		while (db_bits) {
>  			/*
> -			 * pci_epc_raise_irq() for MSI expects a 1-based
> -			 * interrupt number. The first usable doorbell starts
> -			 * at EPF_IRQ_DB_START in the legacy slot layout.
> +			 * pci_epc_raise_irq() expects a 1-based interrupt
> +			 * number for MSI and MSI-X. The first usable doorbell
> +			 * starts at EPF_IRQ_DB_START in the legacy slot layout.
>  			 *
>  			 * Legacy mapping (kept for compatibility):
>  			 *
> -			 *   MSI #1 : link event (reserved)
> -			 *   MSI #2 : unused (historical offset)
> -			 *   MSI #3 : doorbell bit 0 (DB#0)
> -			 *   MSI #4 : doorbell bit 1 (DB#1)
> +			 *   IRQ #1 : link event (reserved)
> +			 *   IRQ #2 : unused (historical offset)
> +			 *   IRQ #3 : doorbell bit 0 (DB#0)
> +			 *   IRQ #4 : doorbell bit 1 (DB#1)
>  			 *   ...
>  			 *
>  			 * Do not change this mapping to avoid breaking
> @@ -1556,7 +1591,7 @@ static void vntb_epf_peer_db_work(struct work_struct *work)
>  			db_bits &= ~BIT_ULL(db_bit);
>
>  			ret = pci_epc_raise_irq(epf->epc, func_no, vfunc_no,
> -						PCI_IRQ_MSI, interrupt_num);
> +						irq_type, interrupt_num);
>  			if (ret)
>  				dev_err(&ntb->ntb.dev,
>  					"Failed to raise IRQ for interrupt_num %u: %d\n",
> --
> 2.51.0
>