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

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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>
This commit is contained in:
Stephan Gerhold 2025-09-08 13:31:22 +02:00 committed by Casey Connolly
parent 4e26c1e2fa
commit 080d19b6e6
1 changed files with 0 additions and 3 deletions
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3
drivers/serial/serial_msm.c
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@ -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");