[PDDF] multifpgapci driver - Add mdio support #24348

lotus-nexthop · 2025-10-27T04:21:10Z

Why I did it

NH-5010 uses the FPGA as an MDIO controller
We desire to use the PDDF FPGA driver to create the kernel MDIO buses

Example usage: https://github.com/sonic-net/sonic-buildimage/blob/master/device/nexthop/x86_64-nexthop_5010-r0/pddf/pddf-device.json.j2#L2005-L2011

    "pddf_kos": [
      "pddf_multifpgapci_mdio_module",
      "pddf_multifpgapci_driver",
      "pddf_multifpgapci_module",
      ...
    ],
    "custom_kos": [
      "pddf_custom_mdio_algo",
      ...
    ]
  },
  "MULTIFPGAPCIE1": {
    "dev_info": {
      "device_type": "MULTIFPGAPCIE",
      "device_name": "SWITCHCARD_FPGA",
      ...
    },
    ...
    "mdio": {
      "dev_attr": {
        "ch_base_offset": "0x4200",
        "ch_size": "0x10",
        "num_virt_ch": "0x10"
      }
    }
  },

Resulting pddf_parse.py commands run for mdio

echo '0x4200' > /sys/kernel/pddf/devices/multifpgapci/0000:03:00.0/mdio/ch_base_offset
echo '0x10' > /sys/kernel/pddf/devices/multifpgapci/0000:03:00.0/mdio/ch_size
echo '0x10' > /sys/kernel/pddf/devices/multifpgapci/0000:03:00.0/mdio/num_virt_ch
echo 'fpgapci_init' > /sys/kernel/pddf/devices/multifpgapci/0000:03:00.0/dev_ops
echo 0 > /sys/kernel/pddf/devices/multifpgapci/0000:03:00.0/mdio/new_mdio_bus
echo 1 > /sys/kernel/pddf/devices/multifpgapci/0000:03:00.0/mdio/new_mdio_bus
echo 2 > /sys/kernel/pddf/devices/multifpgapci/0000:03:00.0/mdio/new_mdio_bus
echo 3 > /sys/kernel/pddf/devices/multifpgapci/0000:03:00.0/mdio/new_mdio_bus
echo 4 > /sys/kernel/pddf/devices/multifpgapci/0000:03:00.0/mdio/new_mdio_bus
echo 5 > /sys/kernel/pddf/devices/multifpgapci/0000:03:00.0/mdio/new_mdio_bus
echo 6 > /sys/kernel/pddf/devices/multifpgapci/0000:03:00.0/mdio/new_mdio_bus
echo 7 > /sys/kernel/pddf/devices/multifpgapci/0000:03:00.0/mdio/new_mdio_bus
echo 8 > /sys/kernel/pddf/devices/multifpgapci/0000:03:00.0/mdio/new_mdio_bus
echo 9 > /sys/kernel/pddf/devices/multifpgapci/0000:03:00.0/mdio/new_mdio_bus
echo 10 > /sys/kernel/pddf/devices/multifpgapci/0000:03:00.0/mdio/new_mdio_bus
echo 11 > /sys/kernel/pddf/devices/multifpgapci/0000:03:00.0/mdio/new_mdio_bus
echo 12 > /sys/kernel/pddf/devices/multifpgapci/0000:03:00.0/mdio/new_mdio_bus
echo 13 > /sys/kernel/pddf/devices/multifpgapci/0000:03:00.0/mdio/new_mdio_bus
echo 14 > /sys/kernel/pddf/devices/multifpgapci/0000:03:00.0/mdio/new_mdio_bus
echo 15 > /sys/kernel/pddf/devices/multifpgapci/0000:03:00.0/mdio/new_mdio_bus

Resulting mdio buses in sysfs

admin@humm120-dut:~$ ls /sys/class/mdio_bus/
0000:07:00.3  pci-mdio-0  pci-mdio-10  pci-mdio-12  pci-mdio-14  pci-mdio-2  pci-mdio-4  pci-mdio-6  pci-mdio-8
fixed-0       pci-mdio-1  pci-mdio-11  pci-mdio-13  pci-mdio-15  pci-mdio-3  pci-mdio-5  pci-mdio-7  pci-mdio-9

Through the mdio_fpga_algo_ops vendors can override the callbacks for the mdio reads and writes without changing the core driver.

In addtion an mdio_acces per an mdio bus sysfs file is exposed for debugging and development purposes.

mdio access API:

Doing a write:
- echo "write <phy_addr> <reg_num> <value>" > mdio_access
Doing a read:
- Set addres to read
  - echo "read <phy_addr> <reg_num>" > mdio_access
- Read back value from address
  - cat mdio_access

Example

root@sonic:/home/admin# echo "write 0x1f 0x18B20 0x1234" > /sys/class/mdio_bus/pci-mdio-0/mdio_access
root@sonic:/home/admin# echo "read 0x1f 0x18B20" > /sys/class/mdio_bus/pci-mdio-0/mdio_access
root@sonic:/home/admin# cat /sys/class/mdio_bus/pci-mdio-0/mdio_access
0x1234

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