On Wed, Jul 14, 2021 at 11:39:34PM +0300, Ramon Fried wrote:
On Wed, Jul 14, 2021 at 11:56 AM Stephan Gerhold stephan@gerhold.net wrote:
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 stephan@gerhold.net
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 <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*/ @@ -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);-- 2.32.0
Eh...this is not a nice fix, perhaps just clearing the RX buffer after initialization will work better ?
I don't like it much either but this is the best I came up with even after spending several hours trying to track down the problem. I also tried porting more register initialization from LK, probably even tried clearing the RX buffer again after initialization.
The problem is: In my tests there was no way to get rid of the delay, because the character doesn't show up until a few milliseconds after initialization. What you suggest would only work like this:
<initialize UART> mdelay(5); // Wait for the weird character to show up <clear RX buffer>
Which is not much different (and in fact will take longer) than:
mdelay(5); <initialize UART>
So unfortunately I can't think of a way to get rid of the delay. :(
I'm not sure if this is some strange problem of my DB410c, I'd actually be curious if the problem can also be reproduced on others.
Stephan