[PATCH 5/5] ARM: dts: stm32: Switch DWMAC RMII clock to MCO2 on DHCOM

[Johann Neuhauser]

> From: Marek Vasut [mailto:marex at denx.de]
> Sent: Tuesday, January 18, 2022 9:30 PM
> 
> 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.
> 
> Signed-off-by: Marek Vasut <marex at denx.de>
> Cc: Alexandre Torgue <alexandre.torgue at foss.st.com>
> Cc: Christophe Roullier <christophe.roullier at foss.st.com>
> Cc: Gabriel Fernandez <gabriel.fernandez at foss.st.com>
> Cc: Patrice Chotard <patrice.chotard at foss.st.com>
> Cc: Patrick Delaunay <patrick.delaunay at foss.st.com>
> Cc: Stephen Boyd <sboyd at kernel.org>
> Cc: linux-clk at vger.kernel.org
> Cc: linux-stm32 at st-md-mailman.stormreply.com
> To: linux-arm-kernel at lists.infradead.org
> ---
>  arch/arm/boot/dts/stm32mp15xx-dhcom-som.dtsi | 22 ++++++++++++++++----
>  1 file changed, 18 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/arm/boot/dts/stm32mp15xx-dhcom-som.dtsi b/arch/arm/boot/dts/stm32mp15xx-dhcom-som.dtsi
> index 8c41f819f7769..b091d9901e976 100644
> --- a/arch/arm/boot/dts/stm32mp15xx-dhcom-som.dtsi
> +++ b/arch/arm/boot/dts/stm32mp15xx-dhcom-som.dtsi
> @@ -116,15 +116,29 @@ &dts {
>         status = "okay";
>  };
> 
> +&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>;
> +};
> +
>  &ethernet0 {
>         status = "okay";
> -       pinctrl-0 = <&ethernet0_rmii_pins_a>;
> -       pinctrl-1 = <&ethernet0_rmii_sleep_pins_a>;
> +       pinctrl-0 = <&ethernet0_rmii_pins_b &mco2_pins_a>;
> +       pinctrl-1 = <&ethernet0_rmii_sleep_pins_b &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 +150,7 @@ phy0: ethernet-phy at 1 {
>                         /* 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>;
> --
> 2.34.1
Tested-by: Johann Neuhauser <jneuhauser at dh-electronics.com>