Merge branch 'dwmac-meson8b-picosecond-precision-rx-delay-support'

Martin Blumenstingl says:

====================
dwmac-meson8b: picosecond precision RX delay support

with the help of Jianxin Pan (many thanks!) the meaning of the "new"
PRG_ETH1[19:16] register bits on Amlogic Meson G12A, G12B and SM1 SoCs
are finally known. These SoCs allow fine-tuning the RGMII RX delay in
200ps steps (contrary to what I have thought in the past [0] these are
not some "calibration" values).

The vendor u-boot has code to automatically detect the best RX/TX delay
settings. For now we keep it simple and add a device-tree property with
200ps precision to select the "right" RX delay for each board.

While here, deprecate the "amlogic,rx-delay-ns" property as it's not
used on any upstream .dts (yet). The driver is backwards compatible.

I have tested this on an X96 Air 4GB board (not upstream yet). Testing
with iperf3 gives 938 Mbits/sec in both directions (RX and TX). The
following network settings were used in the .dts (2ns TX delay
generated by the PHY, 800ps RX delay generated by the MAC as the PHY
only supports 0ns or 2ns RX delays):
        &ext_mdio {
                external_phy: ethernet-phy@0 {
                        /* Realtek RTL8211F (0x001cc916) */
                        reg = <0>;
                        eee-broken-1000t;

                        reset-assert-us = <10000>;
                        reset-deassert-us = <30000>;
                        reset-gpios = <&gpio GPIOZ_15 (GPIO_ACTIVE_LOW |
                                                GPIO_OPEN_DRAIN)>;

                        interrupt-parent = <&gpio_intc>;
                        /* MAC_INTR on GPIOZ_14 */
                        interrupts = <26 IRQ_TYPE_LEVEL_LOW>;
                };
        };

        &ethmac {
                status = "okay";

                pinctrl-0 = <&eth_pins>, <&eth_rgmii_pins>;
                pinctrl-names = "default";

                phy-mode = "rgmii-txid";
                phy-handle = <&external_phy>;

                amlogic,rgmii-rx-delay-ps = <800>;
        };

To use the same settings from vendor u-boot (which in my case has broken
Ethernet) the following commands can be used:
  mw.l 0xff634540 0x1621
  mw.l 0xff634544 0x30000
  phyreg w 0x0 0x1040
  phyreg w 0x1f 0xd08
  phyreg w 0x11 0x9
  phyreg w 0x15 0x11
  phyreg w 0x1f 0x0
  phyreg w 0x0 0x9200

Also I have tested this on a X96 Max board without any .dts changes
to confirm that other boards with the same IP block still work fine
with these changes.

Changes since v3 at [3].
- added Florian's Reviewed-by to patch 1 (thank you!)
- rebased on top of net-next

Changes since v2 at [2]:
- use the generic property name "rx-internal-delay-ps" as suggested by
  Rob (thanks!). This affects patches #1 and #3. The biggest change is
  is in patch #1 which is why I didn't add Florian's and Andrew's
  Reviewed-by
- added Andrew's and Florian's Reviewed-by to patches 2, 3, 4, 5 (many
  thanks to both!). I decided to do this despite renaming the property
  to the generic name "rx-internal-delay-ps" as it only affects the
  patch description and one line of code
- updated patch description of patch #3 to explain why there's not a
  lot of validation when parsing the old device-tree property (in
  nanosecond precision)
- dropped RFC status

Changes since v1 at [1]:
- updated patch 1 by making it more clear when the RX delay is applied.
  Thanks to Andrew for the suggestion!
- added a fix to enabling the timing-adjustment clock only when really
  needed. Found by Andrew - thanks!
- added testing not about X96 Max
- v1 did not go to the netdev mailing list, v2 fixes this

[0] https://lore.kernel.org/netdev/CAFBinCATt4Hi9rigj52nMf3oygyFbnopZcsakGL=KyWnsjY3JA@mail.gmail.com/
[1] https://patchwork.kernel.org/project/linux-amlogic/list/?series=384279&state=%2A&archive=both
[2] https://patchwork.kernel.org/project/linux-amlogic/list/?series=384491&state=%2A&archive=both
[3] https://patchwork.kernel.org/project/linux-amlogic/list/?series=406005&state=%2A&archive=both
====================

Link: https://lore.kernel.org/r/20210106134251.45264-1-martin.blumenstingl@googlemail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>