i.MX7 M4 UART change the speed during linux booting

[max_merchel]

I have a custom imx7 board and use NXP Kernel 4.14 (rel_imx_4.14.78_1.0.0_ga).
On M4 I use the Echo FreeRTOS RTOS API demo. For the M4 UART3 is used.

When I start the M4 in U-Boot, I can read the message

"RPMSG Echo FreeRTOS RTOS API Demo...
RPMSG Init as Remote".

But I can not read the messages on the M4 UART under Linux. I get messages like "���?��q����0��3�9�8�hN��2��y���x�".

Checking the UART shows that the speed of the UART has been increased.

imx7:
uart3: serial@30880000 {
   compatible = "fsl,imx7d-uart",
    "fsl,imx6q-uart";
    reg = <0x30880000 0x10000>;
    interrupts = <GIC_SPI 28 IRQ_TYPE_LEVEL_HIGH>;
    clocks = <&clks IMX7D_UART3_ROOT_CLK>,
    <&clks IMX7D_UART3_ROOT_CLK>;
    clock-names = "ipg", "per";
    dmas = <&sdma 26 4 0>, <&sdma 27 4 0>;
    dma-names = "rx", "tx";
    status = "disabled";
};

Board:
pinctrl_uart3: uart3grp {
   fsl,pins = <
      MX7D_PAD_UART3_RX_DATA__UART3_DCE_RX 0x7e
      MX7D_PAD_UART3_TX_DATA__UART3_DCE_TX 0x76
      MX7D_PAD_UART3_CTS_B__UART3_DCE_CTS 0x76

      MX7D_PAD_UART3_RTS_B__UART3_DCE_RTS 0x7e
   >;
};

&uart3 {
    pinctrl-names = "default";
    pinctrl-0 = <&pinctrl_uart3>;
    assigned-clocks = <&clks IMX7D_UART3_ROOT_SRC>;
    assigned-clock-parents = <&clks IMX7D_OSC_24M_CLK>;

   status = "okay";
};

M4:
&uart3 {
   status = "disabled";
};

[max_merchel · Accepted solution]

Hi igor,

I found the problem at the end of drivers/clk/imx/clk-imx7d.c.

imx_clk_set_parent(clks[IMX7D_UART3_ROOT_SRC], clks[IMX7D_PLL_SYS_MAIN_240M_CLK]); imx_clk_set_rate(clks[IMX7D_UART3_ROOT_DIV], 80000000);

imx_clk_set_parent(clks[IMX7D_UART5_ROOT_SRC], clks[IMX7D_PLL_SYS_MAIN_240M_CLK]); imx_clk_set_rate(clks[IMX7D_UART5_ROOT_DIV], 80000000);

imx_clk_set_parent(clks[IMX7D_UART6_ROOT_SRC], clks[IMX7D_PLL_SYS_MAIN_240M_CLK]); imx_clk_set_rate(clks[IMX7D_UART6_ROOT_DIV], 80000000);

After commenting out the block, I get a readable output on the UART of the M4.

[igorpadykov]

Hi Max

one can try kernel boot parameter uart_from_osc, described in

Table 11. Common kernel boot parameters attached Release Notes or

try to implement similar solution.

Best regards
igor
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[max_merchel]

Hi igor

uart_from_osc didn't change anything.