net: stmmac: dwmac-meson8b: add support for the RX delay configuration
Configure the PRG_ETH0_ADJ_* bits to enable or disable the RX delay based on the various RGMII PHY modes. For now the only supported RX delay settings are: - disabled, use for example for phy-mode "rgmii-id" - 0ns - this is treated identical to "disabled", used for example on boards where the PHY provides 2ns TX delay and the PCB trace length already adds 2ns RX delay - 2ns - for whenever the PHY cannot add the RX delay and the traces on the PCB don't add any RX delay Disabling the RX delay (in case u-boot enables it, which is the case for example on Meson8b Odroid-C1) simply means that PRG_ETH0_ADJ_ENABLE, PRG_ETH0_ADJ_SETUP, PRG_ETH0_ADJ_DELAY and PRG_ETH0_ADJ_SKEW should be disabled (just disabling PRG_ETH0_ADJ_ENABLE may be enough, since that disables the whole re-timing logic - but I find it makes more sense to clear the other bits as well since they depend on that setting). u-boot on Odroid-C1 uses the following steps to enable a 2ns RX delay: - enabling enabling the timing adjustment clock - enabling the timing adjustment logic by setting PRG_ETH0_ADJ_ENABLE - setting the PRG_ETH0_ADJ_SETUP bit The documentation for the PRG_ETH0_ADJ_DELAY and PRG_ETH0_ADJ_SKEW registers indicates that we can even set different RX delays. However, I could not find out how this works exactly, so for now we only support a 2ns RX delay using the exact same way that Odroid-C1's u-boot does. Signed-off-by:Martin Blumenstingl <martin.blumenstingl@googlemail.com> Signed-off-by: