Re: [PATCH] ARM: dts: stm32: Switch DWMAC RMII clock to MCO2 on DHCOM

Hi,

On 7/27/23 00:45, Marek Vasut wrote:

The DHCOM SoM has two options for supplying ETHRX clock to the DWMAC block and PHY. Either (1) ETHCK_K generates 50 MHz clock on ETH_CLK pad for the PHY and the same 50 MHz clock are fed back to ETHRX via internal eth_clk_fb clock connection OR (2) ETH_CLK is not used at all, MCO2 generates 50 MHz clock on MCO2 output pad for the PHY and the same MCO2 clock are fed back into ETHRX via ETH_RX_CLK input pad using external pad-to-pad connection.

Option (1) has two downsides. ETHCK_K is supplied directly from either PLL3_Q or PLL4_P, hence the PLL output is limited to exactly 50 MHz and since the same PLL output is also used to supply SDMMC blocks, the performance of SD and eMMC access is affected. The second downside is that using this option, the EMI of the SoM is higher.

Option (2) solves both of those problems, so implement it here. In this case, the PLL4_P is no longer limited and can be operated faster, at 100 MHz, which improves SDMMC performance (read performance is improved from ~41 MiB/s to ~57 MiB/s with dd if=/dev/mmcblk1 of=/dev/null bs=64M count=1). The EMI interference also decreases.

Ported from Linux kernel commit 73ab99aad50cd ("ARM: dts: stm32: Switch DWMAC RMII clock to MCO2 on DHCOM")

Signed-off-by: Marek Vasut marex@denx.de

Cc: Patrice Chotard patrice.chotard@foss.st.com Cc: Patrick Delaunay patrick.delaunay@foss.st.com Cc: u-boot@dh-electronics.com Cc: uboot-stm32@st-md-mailman.stormreply.com

---

arch/arm/dts/stm32mp15xx-dhcom-som.dtsi | 22 ++++++++++++++++++---- 1 file changed, 18 insertions(+), 4 deletions(-)

diff --git a/arch/arm/dts/stm32mp15xx-dhcom-som.dtsi b/arch/arm/dts/stm32mp15xx-dhcom-som.dtsi index 83e2c87713f..238a611192e 100644 --- a/arch/arm/dts/stm32mp15xx-dhcom-som.dtsi +++ b/arch/arm/dts/stm32mp15xx-dhcom-som.dtsi @@ -118,13 +118,12 @@

&ethernet0 { status = "okay";

• pinctrl-0 = <&ethernet0_rmii_pins_a>;
• pinctrl-1 = <&ethernet0_rmii_sleep_pins_a>;

• pinctrl-0 = <&ethernet0_rmii_pins_c &mco2_pins_a>;
• pinctrl-1 = <&ethernet0_rmii_sleep_pins_c &mco2_sleep_pins_a>; pinctrl-names = "default", "sleep"; phy-mode = "rmii"; max-speed = <100>; phy-handle = <&phy0>;

• st,eth-ref-clk-sel;

  mdio0 { #address-cells = <1>;

@@ -136,7 +135,7 @@ /* LAN8710Ai */ compatible = "ethernet-phy-id0007.c0f0", "ethernet-phy-ieee802.3-c22";

• 	clocks = <&rcc ETHCK_K>;
  

• 	clocks = <&rcc CK_MCO2>;
  reset-gpios = <&gpioh 3 GPIO_ACTIVE_LOW>;
  reset-assert-us = <500>;
  reset-deassert-us = <500>;
  

@@ -446,6 +445,21 @@ }; };

+&rcc {

• /* Connect MCO2 output to ETH_RX_CLK input via pad-pad connection */
• clocks = <&rcc CK_MCO2>;
• clock-names = "ETH_RX_CLK/ETH_REF_CLK";
• /*

• * Set PLL4P output to 100 MHz to supply SDMMC with faster clock,
  

• * set MCO2 output to 50 MHz to supply ETHRX clock with PLL4P/2,
  

• * so that MCO2 behaves as a divider for the ETHRX clock here.
  

• */
  

• assigned-clocks = <&rcc CK_MCO2>, <&rcc PLL4_P>;
• assigned-clock-parents = <&rcc PLL4_P>;
• assigned-clock-rates = <50000000>, <100000000>;

+};

• &rng1 { status = "okay"; };

Reviewed-by: Patrick Delaunay patrick.delaunay@foss.st.com

ok for device tree alignment

but this MCO2 assignment if not functional in U-Boot clock driver

- set_parent() => is not defined

- set_rate() => is only supported for a limited number of clock, PLL4_Q for example

but OK as the MCO2 is already configured in the clock tree directly in U-Boot SPL:

./arch/arm/dts/stm32mp15xx-dhcom-u-boot.dtsi

&rcc {     st,clksrc = < ...         CLK_MCO2_PLL4P     >;

st,clkdiv = < ...         1 /*MCO2*/     >;

Thanks Patrick