From: Martin Blumenstingl martin.blumenstingl@googlemail.com
[ Upstream commit f87777a3c30cf50c66a20e1d153f0e003bb30774 ]
The dwmac glue registers on Amlogic Meson8b and newer SoCs has two clock inputs: - Meson8b and Meson8m2: MPLL2 and MPLL2 (the same parent is wired to both inputs) - GXBB, GXL, GXM, AXG, G12A, G12B, SM1: FCLK_DIV2 and MPLL2
All known vendor kernels and u-boots are using the first input only. We let the common clock framework automatically choose the "right" parent. For some boards this causes a problem though, specificially with G12A and newer SoCs. The clock input is used for generating the 125MHz RGMII TX clock. For the two input clocks this means on G12A: - FCLK_DIV2: 999999985Hz / 8 = 124999998.125Hz - MPLL2: 499999993Hz / 4 = 124999998.25Hz
In theory MPLL2 is the "better" clock input because it's gets us 0.125Hz closer to the requested frequency than FCLK_DIV2. In reality however there is a resource conflict because MPLL2 is needed to generate some of the audio clocks. dwmac-meson8b probes first and sets up the clock tree with MPLL2. This works fine until the audio driver comes and "steals" the MPLL2 clocks and configures it with it's own rate (294909637Hz). The common clock framework happily changes the MPLL2 rate but does not reconfigure our RGMII TX clock tree, which then ends up at 73727409Hz, which is more than 40% off the requested 125MHz.
Don't use the second clock input for now to force the common clock framework to always select the first parent. This mimics the behavior from the vendor driver and fixes the clock resource conflict with the audio driver on G12A boards. Once the common clock framework can handle this situation this change can be reverted again.
Fixes: 566e8251625304 ("net: stmmac: add a glue driver for the Amlogic Meson 8b / GXBB DWMAC") Reported-by: Thomas Graichen thomas.graichen@gmail.com Signed-off-by: Martin Blumenstingl martin.blumenstingl@googlemail.com Tested-by: thomas graichen thomas.graichen@gmail.com Link: https://lore.kernel.org/r/20201219135036.3216017-1-martin.blumenstingl@googl... Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/net/ethernet/stmicro/stmmac/dwmac-meson8b.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/drivers/net/ethernet/stmicro/stmmac/dwmac-meson8b.c +++ b/drivers/net/ethernet/stmicro/stmmac/dwmac-meson8b.c @@ -135,7 +135,7 @@ static int meson8b_init_rgmii_tx_clk(str struct device *dev = dwmac->dev; static const struct clk_parent_data mux_parents[] = { { .fw_name = "clkin0", }, - { .fw_name = "clkin1", }, + { .index = -1, }, }; static const struct clk_div_table div_table[] = { { .div = 2, .val = 2, },