net: ethernet: oa_tc6: Handle the OA TC6 SPI protected mode

Implement the OA TC6 standard defined protected mode for control (register
access) transactions. In addition to the current register access formats
the oa_tc6 driver handles, 1's complement values of the data field
are included (by both the host and the MACPHY) in the SPI transfer frames.
This feature acts as an integrity check.

Control write transactions look like this:

          |<- 32 bits ->|<--- data_size --->|<- 32 bits ->|
    MOSI: | ctrl header | reg write data    | ignored     |
    MISO: | (discard)   | echoed ctrl hdr   | echoed data |

    data_size (LEN = number of registers to read in a sequence):
      Unprotected: 32 x (LEN + 1) bits
      Protected:   2 x 32 x (LEN + 1) bits

Control read transaction:

          |<- 32 bits ->|<--- 32 bits --> |<- data_size ->|
    MOSI: | ctrl header | ignored ...                     |
    MISO: | (discard)   | echoed ctrl hdr | reg read data |

    data_size (LEN = number of registers to read in a sequence):
      Unprotected: 32 x (LEN + 1) bits
      Protected:   2 x 32 x (LEN + 1) bits

Register data format ("reg write data" and "reg read data"):

    Unprotected:
      | W1 (normal) | W2 (normal) | ... | Wx (normal) |

    Protected:
    | W1 (normal) | W1 (complement) | ... | Wx (normal) | Wx (complement)|

The protected mode state can be read from the bit 5 of CONFIG0 (0x4)
register, and this setting is usually only configured during the
MACPHY's reset (depending on the device it can be done by setting the
state of a pin). We can read the protected mode configuration before any
other register access and since the SPI transfer is initially sized for an
unprotected read, the MACPHY's complement words are never clocked out
and no checking is required. The data transactions (Ethernet frames)
remain unchanged.

Signed-off-by: Ciprian Regus <ciprian.regus@analog.com>
Link: https://patch.msgid.link/20260708-adin1140-driver-v5-2-4aca7b51a58b@analog.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

0 files changed, 0 insertions, 0 deletions