Re: [PATCH v2] ARM: dts: stm32: Switch DWMAC RMII clock to MCO2 on DHCOM

[Patrice CHOTARD]

On 7/27/23 01:58, 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 <ma...@denx.de>
> ---
> Cc: Patrice Chotard <patrice.chot...@foss.st.com>
> Cc: Patrick Delaunay <patrick.delau...@foss.st.com>
> Cc: u-b...@dh-electronics.com
> Cc: uboot-st...@st-md-mailman.stormreply.com
> ---
> V2: Add U-Boot specifics to cater also for clock and clock-names in 
> stm32mp151.dtsi
> ---
>  arch/arm/dts/stm32mp15xx-dhcom-som.dtsi    | 22 ++++++++++++++++++----
>  arch/arm/dts/stm32mp15xx-dhcom-u-boot.dtsi | 14 ++++++++++++++
>  2 files changed, 32 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";
>  };
> diff --git a/arch/arm/dts/stm32mp15xx-dhcom-u-boot.dtsi 
> b/arch/arm/dts/stm32mp15xx-dhcom-u-boot.dtsi
> index bc0730cf2bd..ff5e9034951 100644
> --- a/arch/arm/dts/stm32mp15xx-dhcom-u-boot.dtsi
> +++ b/arch/arm/dts/stm32mp15xx-dhcom-u-boot.dtsi
> @@ -126,6 +126,20 @@
>  };
>  
>  &rcc {
> +     /*
> +      * Reinstate clock names from stm32mp151.dtsi, the MCO2 trick
> +      * used in stm32mp15xx-dhcom-som.dtsi is not supported by the
> +      * U-Boot clock framework.
> +      */
> +     clock-names = "hse", "hsi", "csi", "lse", "lsi";
> +     clocks = <&clk_hse>, <&clk_hsi>, <&clk_csi>,
> +              <&clk_lse>, <&clk_lsi>;
> +
> +     /* The MCO2 is already configured correctly, remove those. */
> +     /delete-property/ assigned-clocks;
> +     /delete-property/ assigned-clock-parents;
> +     /delete-property/ assigned-clock-rates;
> +
>       st,clksrc = <
>               CLK_MPU_PLL1P
>               CLK_AXI_PLL2P
Reviewed-by: Patrice Chotard <patrice.chot...@foss.st.com>

Thanks
Patrice