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Date: Sat, 13 Apr 2024 21:11:16 +0200
From: "Arnd Bergmann" <arnd@arndb.de>
To: "Vamsi Attunuru" <vattunuru@marvell.com>,
 "Greg Kroah-Hartman" <gregkh@linuxfoundation.org>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
 "Jerin Jacob" <jerinj@marvell.com>
Subject: Re: [EXTERNAL] Re: [PATCH v5 1/1] misc: mrvl-cn10k-dpi: add Octeon CN10K DPI
 administrative driver
Content-Type: text/plain

On Sat, Apr 13, 2024, at 18:17, Vamsi Krishna Attunuru wrote:
> From: Greg KH <gregkh@linuxfoundation.org>
>> On Sat, Apr 13, 2024 at 10:58:37AM +0000, Vamsi Krishna Attunuru wrote:
>> > From: Greg KH <gregkh@linuxfoundation.org>
>> >
>> > No, it's a normal PCIe sriov capability implemented in all sriov capable PCIe
>> devices.
>> > Our PF device aka this driver in kernel space service mailbox requests
>> > from userspace applications via VF devices. For instance, DPI VF
>> > device from user space writes into mailbox registers and the DPI hardware
>> triggers an interrupt to DPI PF device.
>> > Upon PF interrupt, this driver services the mailbox requests.
>> 
>> Isn't that a "normal" PCI thing?  How is this different from other devices that
>> have VF?
>
> Looks like there is a lot of confusion for this device. Let me explain
> There are two aspects for this DPI PF device.
> a) It's a PCIe device so it is "using" some of the PCI services 
> provided PCIe HW or PCI subsystem
> b) It is "providing" non PCIe service(DPI HW administrative function) 
> by using (a)
> Let me enumerate PF device operations with above aspects.
> 1) Means to create VF(s) from PF. It's category (a) service and driver 
> uses API (pci_sriov_configure_simple()) from PCI subsystem to implement 
> it.
> 2) Means to get the interrupt(mailbox or any device specific 
> interrupt). It's category (a) service and driver uses API 
> (pci_alloc_irq_vectors()) from PCI subsystem to implement it.
> 3) Means to get the mailbox content from VF by using (2). It's category 
> (b) service. This service is not part of PCI specification.
> DPI PF device has the mailbox registers(DPI_MBOX_PF_VF_DATA registers) 
> in its PCIe BAR space which are device specific.
> 4) Upon receiving DPI HW administrative function mailbox request, 
> service it. Its category (b) service. This service is not part of PCI 
> specification.
> For instance, dpi_queue_open & close are requests sent from DPI VF 
> device to DPI PF device for setting up the DPI VF queue resources. Once 
> its setup by DPI PF,
> then DPI VF device can use these queues. These queues are not part of 
> PCIe specification. These queues are used for making DMA by DPI VF 
> device/driver.

It's not directly my area either, but as far as I can tell
from reading the competing sr-iov based device drivers, these
seem to handle all of the above in the network driver that
owns the PF rather than a separate driver, e.g. for the
first point:

$ git grep -w sriov_configure.= drivers/net/
drivers/net/ethernet/amazon/ena/ena_netdev.c:   .sriov_configure = pci_sriov_configure_simple,
drivers/net/ethernet/amd/pds_core/main.c:       .sriov_configure = pdsc_sriov_configure,
drivers/net/ethernet/broadcom/bnx2x/bnx2x_main.c:       .sriov_configure = bnx2x_sriov_configure,
drivers/net/ethernet/broadcom/bnxt/bnxt.c:      .sriov_configure = bnxt_sriov_configure,
drivers/net/ethernet/cavium/liquidio/lio_main.c:        .sriov_configure = liquidio_enable_sriov,
drivers/net/ethernet/chelsio/cxgb4/cxgb4_main.c:        .sriov_configure = cxgb4_iov_configure,
drivers/net/ethernet/emulex/benet/be_main.c:    .sriov_configure = be_pci_sriov_configure,
drivers/net/ethernet/freescale/enetc/enetc_pf.c:        .sriov_configure = enetc_sriov_configure,
drivers/net/ethernet/fungible/funeth/funeth_main.c:     .sriov_configure = funeth_sriov_configure,
drivers/net/ethernet/hisilicon/hns3/hns3_enet.c:        .sriov_configure = hns3_pci_sriov_configure,
drivers/net/ethernet/huawei/hinic/hinic_main.c: .sriov_configure = hinic_pci_sriov_configure,
drivers/net/ethernet/intel/fm10k/fm10k_pci.c:   .sriov_configure        = fm10k_iov_configure,
drivers/net/ethernet/intel/i40e/i40e_main.c:    .sriov_configure = i40e_pci_sriov_configure,
drivers/net/ethernet/intel/ice/ice_main.c:      .sriov_configure = ice_sriov_configure,
drivers/net/ethernet/intel/idpf/idpf_main.c:    .sriov_configure        = idpf_sriov_configure,
drivers/net/ethernet/intel/igb/igb_main.c:      .sriov_configure = igb_pci_sriov_configure,
drivers/net/ethernet/intel/ixgbe/ixgbe_main.c:  .sriov_configure = ixgbe_pci_sriov_configure,
drivers/net/ethernet/marvell/octeon_ep/octep_main.c:    .sriov_configure = octep_sriov_configure,
drivers/net/ethernet/marvell/octeontx2/nic/otx2_pf.c:   .sriov_configure = otx2_sriov_configure
drivers/net/ethernet/netronome/nfp/nfp_main.c:  .sriov_configure        = nfp_pcie_sriov_configure,
drivers/net/ethernet/pensando/ionic/ionic_bus_pci.c:    .sriov_configure = ionic_sriov_configure,
drivers/net/ethernet/qlogic/qede/qede_main.c:   .sriov_configure = qede_sriov_configure,
drivers/net/ethernet/qlogic/qlcnic/qlcnic_main.c:       .sriov_configure = qlcnic_pci_sriov_configure,
drivers/net/ethernet/sfc/ef10.c:        .sriov_configure = efx_ef10_sriov_configure,
drivers/net/ethernet/sfc/ef100.c:       .sriov_configure = ef100_pci_sriov_configure,
drivers/net/ethernet/sfc/ef100_nic.c:   .sriov_configure = IS_ENABLED(CONFIG_SFC_SRIOV) ?
drivers/net/ethernet/sfc/efx.c: .sriov_configure = efx_pci_sriov_configure,
drivers/net/ethernet/sfc/siena/efx.c:   .sriov_configure = efx_pci_sriov_configure,
drivers/net/ethernet/sfc/siena/siena.c: .sriov_configure = efx_siena_sriov_configure,

In what way is your hardware different from all the others?

     Arnd