From: Martin Blumenstingl martin.blumenstingl@googlemail.com
[ Upstream commit fb7d38a70e1d8ffd54f7a7464dcc4889d7e490ad ]
On Meson8b the only valid input clock is MPLL2. The bootloader configures that to run at 500002394Hz which cannot be divided evenly down to 125MHz using the m250_div clock. Currently the common clock framework chooses a m250_div of 2 - with the internal fixed "divide by 10" this results in a RGMII TX clock of 125001197Hz (120Hz above the requested 125MHz).
Letting the common clock framework propagate the rate changes up to the parent of m250_mux allows us to get the best possible clock rate. With this patch the common clock framework calculates a rate of very-close-to-250MHz (249999701Hz to be exact) for the MPLL2 clock (which is the mux input). Dividing that by 2 (which is an internal, fixed divider for the RGMII TX clock) gives us an RGMII TX clock of 124999850Hz (which is only 150Hz off the requested 125MHz, compared to 1197Hz based on the MPLL2 rate set by u-boot and the Amlogic GPL kernel sources).
SoCs from the Meson GX series are not affected by this change because the input clock is FCLK_DIV2 whose rate cannot be changed (which is fine since it's running at 1GHz, so it's already a multiple of 250MHz and 125MHz).
Fixes: 566e8251625304 ("net: stmmac: add a glue driver for the Amlogic Meson 8b / GXBB DWMAC") Suggested-by: Jerome Brunet jbrunet@baylibre.com Signed-off-by: Martin Blumenstingl martin.blumenstingl@googlemail.com Reviewed-by: Jerome Brunet jbrunet@baylibre.com Tested-by: Jerome Brunet jbrunet@baylibre.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Sasha Levin alexander.levin@microsoft.com --- drivers/net/ethernet/stmicro/stmmac/dwmac-meson8b.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac-meson8b.c b/drivers/net/ethernet/stmicro/stmmac/dwmac-meson8b.c index 923033867a4d..f356a44bcb81 100644 --- a/drivers/net/ethernet/stmicro/stmmac/dwmac-meson8b.c +++ b/drivers/net/ethernet/stmicro/stmmac/dwmac-meson8b.c @@ -118,7 +118,7 @@ static int meson8b_init_clk(struct meson8b_dwmac *dwmac) snprintf(clk_name, sizeof(clk_name), "%s#m250_sel", dev_name(dev)); init.name = clk_name; init.ops = &clk_mux_ops; - init.flags = 0; + init.flags = CLK_SET_RATE_PARENT; init.parent_names = mux_parent_names; init.num_parents = MUX_CLK_NUM_PARENTS;