[PATCH 0/2] serial: lpuart: fix RXFE filed offset and handle Overrun flag

[PATCH 0/2] serial: lpuart: fix RXFE filed offset and handle Overrun flag

[Sébastien Szymanski]

This couple patches fixes the RXFE filed offset on i.MX9 platforms and handle
the Overrun flag which can prevent user from accessing the U-Boot prompt.

Signed-off-by: Sébastien Szymanski <sebastien.szymanski@armadeus.com>
---
Sébastien Szymanski (2):
      serial: lpuart: fix RXFE filed offset for i.MX9
      serial: lpuart: handle Overrun flag

 drivers/serial/serial_lpuart.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)
---
base-commit: 8666b16015d4212facacc514e2eb626f3630dcf0
change-id: 20260218-lpuart-fix-rxfe-offset-f04ef861ae99

Best regards,
-- 
Sébastien Szymanski <sebastien.szymanski@armadeus.com>

[PATCH 1/2] serial: lpuart: fix RXFE filed offset for i.MX9

[Sébastien Szymanski]

Like i.MX8 and i.MXRT, on i.MX9, the Receive RX FIFO Enable (RXFE) field
in LPUART FIFO register is bit 3, so set FIFO_RXFE to 0x08 on i.MX9 too.

Signed-off-by: Sébastien Szymanski <sebastien.szymanski@armadeus.com>
---
 drivers/serial/serial_lpuart.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/serial/serial_lpuart.c b/drivers/serial/serial_lpuart.c
index 9fdb6503085d..bbce59443388 100644
--- a/drivers/serial/serial_lpuart.c
+++ b/drivers/serial/serial_lpuart.c
@@ -53,7 +53,8 @@
 #define FIFO_RXSIZE_MASK	0x7
 #define FIFO_RXSIZE_OFF	0
 #define FIFO_TXFE		0x80
-#if defined(CONFIG_ARCH_IMX8) || defined(CONFIG_ARCH_IMXRT)
+#if defined(CONFIG_ARCH_IMX8) || defined (CONFIG_ARCH_IMX9) || \
+    defined(CONFIG_ARCH_IMXRT)
 #define FIFO_RXFE		0x08
 #else
 #define FIFO_RXFE		0x40

-- 
2.52.0

RE: [PATCH 1/2] serial: lpuart: fix RXFE filed offset for i.MX9

[Peng Fan (OSS)]

> Subject: [PATCH 1/2] serial: lpuart: fix RXFE filed offset for i.MX9
> 
> Like i.MX8 and i.MXRT, on i.MX9, the Receive RX FIFO Enable (RXFE)
> field in LPUART FIFO register is bit 3, so set FIFO_RXFE to 0x08 on
> i.MX9 too.
> 
> Signed-off-by: Sébastien Szymanski
> <sebastien.szymanski@armadeus.com>

LGTM: Reviewed-by: Peng Fan <peng.fan@nxp.com>

Re: [PATCH 1/2] serial: lpuart: fix RXFE filed offset for i.MX9

[Ye Li]

On 2/18/2026 10:59 PM, Sébastien Szymanski wrote:
> Like i.MX8 and i.MXRT, on i.MX9, the Receive RX FIFO Enable (RXFE) field
> in LPUART FIFO register is bit 3, so set FIFO_RXFE to 0x08 on i.MX9 too.
> 
> Signed-off-by: Sébastien Szymanski <sebastien.szymanski@armadeus.com>
> ---
>   drivers/serial/serial_lpuart.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/serial/serial_lpuart.c b/drivers/serial/serial_lpuart.c
> index 9fdb6503085d..bbce59443388 100644
> --- a/drivers/serial/serial_lpuart.c
> +++ b/drivers/serial/serial_lpuart.c
> @@ -53,7 +53,8 @@
>   #define FIFO_RXSIZE_MASK	0x7
>   #define FIFO_RXSIZE_OFF	0
>   #define FIFO_TXFE		0x80
> -#if defined(CONFIG_ARCH_IMX8) || defined(CONFIG_ARCH_IMXRT)
> +#if defined(CONFIG_ARCH_IMX8) || defined (CONFIG_ARCH_IMX9) || \
> +    defined(CONFIG_ARCH_IMXRT)
>   #define FIFO_RXFE		0x08
>   #else
>   #define FIFO_RXFE		0x40

Previous value 0x40 is wrong for all platforms. You can directly change 
it to 0x08 and remove all ARCH marcos.

Best regards,
Ye Li
> 

[PATCH 2/2] serial: lpuart: handle Overrun flag

[Sébastien Szymanski]

The receive FIFO may overflow if data are sent while U-Boot is still
booting. In that case, the Overrun flag (STAT[19]) is set and no
additional data is stored in the receive FIFO and the user cannot get
access to the U-Boot prompt.

Fix this by clearing the Overrun flag in _lpuart32_serial_tstc()

Signed-off-by: Sébastien Szymanski <sebastien.szymanski@armadeus.com>
---
 drivers/serial/serial_lpuart.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/serial/serial_lpuart.c b/drivers/serial/serial_lpuart.c
index bbce59443388..0728feccd131 100644
--- a/drivers/serial/serial_lpuart.c
+++ b/drivers/serial/serial_lpuart.c
@@ -367,10 +367,13 @@ static int _lpuart32_serial_putc(struct lpuart_serial_plat *plat,
 static int _lpuart32_serial_tstc(struct lpuart_serial_plat *plat)
 {
 	struct lpuart_fsl_reg32 *base = plat->reg;
-	u32 water;
+	u32 water, stat;
 
-	lpuart_read32(plat->flags, &base->water, &water);
+	lpuart_read32(plat->flags, &base->stat, &stat);
+	if (stat & STAT_OR)
+		lpuart_write32(plat->flags, &base->stat, STAT_OR);
 
+	lpuart_read32(plat->flags, &base->water, &water);
 	if ((water >> 24) == 0)
 		return 0;
 

-- 
2.52.0

RE: [PATCH 2/2] serial: lpuart: handle Overrun flag

[Peng Fan (OSS)]

> Subject: [PATCH 2/2] serial: lpuart: handle Overrun flag
> 
> The receive FIFO may overflow if data are sent while U-Boot is still
> booting. In that case, the Overrun flag (STAT[19]) is set and no
> additional data is stored in the receive FIFO and the user cannot get
> access to the U-Boot prompt.
> 
> Fix this by clearing the Overrun flag in _lpuart32_serial_tstc()
> 
> Signed-off-by: Sébastien Szymanski
> <sebastien.szymanski@armadeus.com>

LGTM: Reviewed-by: Peng Fan <peng.fan@nxp.com>

Re: [PATCH 0/2] serial: lpuart: fix RXFE filed offset and handle Overrun flag

[Kory Maincent]

On Wed, 18 Feb 2026 15:59:17 +0100
Sébastien Szymanski <sebastien.szymanski@armadeus.com> wrote:

> This couple patches fixes the RXFE filed offset on i.MX9 platforms and handle
> the Overrun flag which can prevent user from accessing the U-Boot prompt.

Reviewed-by: Kory Maincent <kory.maincent@bootlin.com>

Thank you!
-- 
Köry Maincent, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com