• Martin Blumenstingl's avatar
    net: stmmac: dwmac-meson8b: fix setting the RGMII TX clock on Meson8b · 433c6cab
    Martin Blumenstingl authored
    Meson8b only supports MPLL2 as clock input. The rate of the MPLL2 clock
    set by Odroid-C1's u-boot is close to (but not exactly) 500MHz. The
    exact rate is 500002394Hz, which is calculated in
    drivers/clk/meson/clk-mpll.c using the following formula:
    DIV_ROUND_UP_ULL((u64)parent_rate * SDM_DEN, (SDM_DEN * n2) + sdm)
    Odroid-C1's u-boot configures MPLL2 with the following values:
    - SDM_DEN = 16384
    - SDM = 1638
    - N2 = 5
    
    The 250MHz clock (m250_div) inside dwmac-meson8b driver is derived from
    the MPLL2 clock. Due to MPLL2 running slightly faster than 500MHz the
    common clock framework chooses a divider which is too big to generate
    the 250MHz clock (a divider of 2 would be needed, but this is rounded up
    to a divider of 3). This breaks the RTL8211F RGMII PHY on Odroid-C1
    because it requires a (close to) 125MHz RGMII TX clock (on Gbit speeds,
    the IP block internally divides that down to 25MHz on 100Mbit/s
    connections and 2.5MHz on 10Mbit/s connections - we don't need any
    special configuration for that).
    
    Round the divider to the closest value to prevent this issue on Meson8b.
    This means we'll now end up with a clock rate for the RGMII TX clock of
    125001197Hz (= 125MHz plus 1197Hz), which is close-enough to 125MHz.
    This has no effect on the Meson GX SoCs since there fclk_div2 is used as
    input clock, which has a rate of 1000MHz (and thus is divisible cleanly
    to 250MHz and 125MHz).
    
    Fixes: 566e8251 ("net: stmmac: add a glue driver for the Amlogic Meson 8b / GXBB DWMAC")
    Reported-by: default avatarEmiliano Ingrassia <ingrassia@epigenesys.com>
    Signed-off-by: default avatarMartin Blumenstingl <martin.blumenstingl@googlemail.com>
    Reviewed-by: default avatarJerome Brunet <jbrunet@baylibre.com>
    Tested-by: default avatarJerome Brunet <jbrunet@baylibre.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    433c6cab
dwmac-meson8b.c 10 KB