Commit 433c6cab authored by Martin Blumenstingl's avatar Martin Blumenstingl Committed by David S. Miller

net: stmmac: dwmac-meson8b: fix setting the RGMII TX clock on Meson8b

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>
parent 4f6a71b8
......@@ -140,7 +140,9 @@ static int meson8b_init_rgmii_tx_clk(struct meson8b_dwmac *dwmac)
dwmac->m250_div.shift = PRG_ETH0_CLK_M250_DIV_SHIFT;
dwmac->m250_div.width = PRG_ETH0_CLK_M250_DIV_WIDTH;
dwmac->m250_div.hw.init = &init;
dwmac->m250_div.flags = CLK_DIVIDER_ONE_BASED | CLK_DIVIDER_ALLOW_ZERO;
dwmac->m250_div.flags = CLK_DIVIDER_ONE_BASED |
CLK_DIVIDER_ALLOW_ZERO |
CLK_DIVIDER_ROUND_CLOSEST;
dwmac->m250_div_clk = devm_clk_register(dev, &dwmac->m250_div.hw);
if (WARN_ON(IS_ERR(dwmac->m250_div_clk)))
......
Markdown is supported
0%
or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment