From ad7e967738a9c639e07cf50b83ffccdf9a8537b0 Mon Sep 17 00:00:00 2001 From: Stephan Gerhold Date: Wed, 14 Jul 2021 10:56:26 +0200 Subject: [PATCH] serial: serial_msm: Delay initialization to let pins stabilize For some reason, the DragonBoard 410c aborts autoboot immediately if U-Boot is started without LK. It looks like it picks up a single broken character via serial and therefore believes a key was pressed to abort autoboot. After some debugging, it seems like adding some delay after pinctrl setup but before UART initialization fixes the issue. It's also worth mentioning that unlike when booting from LK, the pinctrl setup is actually necessary when booting U-Boot without LK since UART is broken if the pinctrl line is removed. I suspect that reconfiguring the pins might take some time to stabilize and if the UART controller is enabled too quickly it will pick up some random noise. Adding a few milliseconds of delay fixes the issue and shouldn't have any other negative side effects. 3ms seems to be the minimum delay required in my tests, use 5ms instead just to be sure. Signed-off-by: Stephan Gerhold --- drivers/serial/serial_msm.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/drivers/serial/serial_msm.c b/drivers/serial/serial_msm.c index d8dd5c1104..ac4d0824b9 100644 --- a/drivers/serial/serial_msm.c +++ b/drivers/serial/serial_msm.c @@ -18,6 +18,7 @@ #include #include #include +#include #include /* Serial registers - this driver works in uartdm mode*/ @@ -193,6 +194,9 @@ static int msm_uart_clk_init(struct udevice *dev) static void uart_dm_init(struct msm_serial_data *priv) { + /* Delay initialization for a bit to let pins stabilize if necessary */ + mdelay(5); + writel(priv->clk_bit_rate, priv->base + UARTDM_CSR); writel(0x0, priv->base + UARTDM_MR1); writel(MSM_BOOT_UART_DM_8_N_1_MODE, priv->base + UARTDM_MR2); -- 2.39.5