[0/4] mvebu a3720 comphy: Fix serdes transmit amplitude

Message

Marek Behún Aug. 17, 2022, 7:31 p.m. UTC

This series adds support for setting serdes transmit amplitude for
ethernet modes (sgmii, 1000base-x, 2500base-x) in the Marvell A3720
comphy driver.

The amplitude is set according to setting in device tree.

Finally the Turris MOX device tree is changed to set the 2500base-x
mode tx amplitude to 1025 mV.

This is needed to fix a weird issue wherein when A3720 sends a packet
to Topaz, and the packet contains a long sequence of 'J's or '\xb5'
bytes (these translate to '010101010101'... in 8b/10b encoding), the
packet may be lost on Topaz due to FCS error. The probability of
loss grows with number of 'J's:

  loss
                         ______
  100%                .-^
                     /
                    /
   50%             /
                  /
                 /
    0%  ______.-^
            90    114    125     number of consecutive 'J's

Marek Behún (4):
  string.h: Add str_has_proper_prefix()
  device property: Add {fwnode/device}_get_tx_p2p_amplitude()
  phy: marvell: phy-mvebu-a3700-comphy: Support changing tx amplitude
    for ethernet
  arm64: dts: armada-3720-turris-mox: Change comphy tx amplitude for
    2500base-x mode

 .../dts/marvell/armada-3720-turris-mox.dts    |  10 ++
 drivers/base/property.c                       | 130 ++++++++++++++++++
 drivers/phy/marvell/phy-mvebu-a3700-comphy.c  | 109 ++++++++++++++-
 include/linux/property.h                      |   5 +
 include/linux/string.h                        |  18 +++
 5 files changed, 271 insertions(+), 1 deletion(-)