Meson8b only supports MPLL2 as clock input. The rate of the MPLL2 clock
set by Odroid-C1's u-boot is close to 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) 25MHz clock.
Round the divider to the closest value to prevent this issue on Meson8b.
This means we'll now end up with a clock rate of 25000120Hz (= 25MHz
plus 120Hz).
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 25MHz).
Fixes: 566e8251625304 ("net: stmmac: add a glue driver for the Amlogic Meson 8b
/ GXBB DWMAC")
Reported-by: Emiliano Ingrassia <[email protected]>
Signed-off-by: Martin Blumenstingl <[email protected]>
Reviewed-by: Jerome Brunet <[email protected]>
---
drivers/net/ethernet/stmicro/stmmac/dwmac-meson8b.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac-meson8b.c
b/drivers/net/ethernet/stmicro/stmmac/dwmac-meson8b.c
index 7199e8c08536..d06106417063 100644
--- a/drivers/net/ethernet/stmicro/stmmac/dwmac-meson8b.c
+++ b/drivers/net/ethernet/stmicro/stmmac/dwmac-meson8b.c
@@ -139,7 +139,9 @@ static int meson8b_init_rgmii_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)))
--
2.15.1
