Revert "serial: serial_msm: Delay initialization to let pins stabilize"

There have been issues with autoboot on DB410c for years, where autoboot
gets interrupted by spurious input on the UART console. Back in 2021, I've
tried to fix this by inserting a delay before UART initialization, but it
has turned out this is not working reliably either.

It looks like the root cause has always been the lack of bias-pull-up,
which was causing the RX line to be floating when UART is disconnected.
The delay does not seem to be needed anymore when applying bias-pull-up,
so drop it again in favor of the proper fix.

This reverts commit ad7e967738a9c639e07cf50b83ffccdf9a8537b0.

Signed-off-by: Stephan Gerhold <stephan.gerhold@linaro.org>
Tested-by: Alexey Minnekhanov <alexeymin@minlexx.ru>
Acked-by: Sumit Garg <sumit.garg@oss.qualcomm.com>
Link: https://lore.kernel.org/r/20250908-db410c-autoboot-fixes-v2-2-316ed98e0143@linaro.org
Signed-off-by: Casey Connolly <kcxt@postmarketos.org>

diff --git a/drivers/serial/serial_msm.c b/drivers/serial/serial_msm.c
index 757e5eaf974fc171c7a56006a218554be1425612..c8df91fca589433e57cd4c25a18d09548715c840 100644 (file)
--- a/drivers/serial/serial_msm.c
+++ b/drivers/serial/serial_msm.c
@@ -17,7 +17,6 @@
 #include <asm/global_data.h>
 #include <asm/io.h>
 #include <linux/compiler.h>
-#include <linux/delay.h>
 #include <dm/pinctrl.h>
 
 /* Serial registers - this driver works in uartdm mode*/
@@ -207,8 +206,6 @@ static int calc_csr_bitrate(struct msm_serial_data *priv)
 
 static void uart_dm_init(struct msm_serial_data *priv)
 {
-       /* Delay initialization for a bit to let pins stabilize if necessary */
-       mdelay(5);
        int bitrate = calc_csr_bitrate(priv);
        if (bitrate < 0) {
                log_warning("Couldn't calculate bit clock divider! Using default\n");