[PATCH] tty: serial: fsl_lpuart: don't break the on-going transfer when global reset

[PATCH] tty: serial: fsl_lpuart: don't break the on-going transfer when global reset

[Sherry Sun]

lpuart_global_reset() shouldn't break the on-going transmit engin, need
to recover the on-going data transfer after reset.

This can help earlycon here, since commit 60f361722ad2 ("serial:
fsl_lpuart: Reset prior to registration") moved lpuart_global_reset()
before uart_add_one_port(), earlycon is writing during global reset,
as global reset will disable the TX and clear the baud rate register,
which caused the earlycon cannot work any more after reset, needs to
restore the baud rate and re-enable the transmitter to recover the
earlycon write.

Fixes: bd5305dcabbc ("tty: serial: fsl_lpuart: do software reset for imx7ulp and imx8qxp")
Signed-off-by: Sherry Sun <sherry.sun@nxp.com>
---
 drivers/tty/serial/fsl_lpuart.c | 23 ++++++++++++++++++++---
 1 file changed, 20 insertions(+), 3 deletions(-)

diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c
index 67fa113f77d4..5064fdba1b61 100644
--- a/drivers/tty/serial/fsl_lpuart.c
+++ b/drivers/tty/serial/fsl_lpuart.c
@@ -408,11 +408,9 @@ static int lpuart_global_reset(struct lpuart_port *sport)
 {
 	struct uart_port *port = &sport->port;
 	void __iomem *global_addr;
+	unsigned long tx_enable, bd, stat, sfifo;
 	int ret;
 
-	if (uart_console(port))
-		return 0;
-
 	ret = clk_prepare_enable(sport->ipg_clk);
 	if (ret) {
 		dev_err(sport->port.dev, "failed to enable uart ipg clk: %d\n", ret);
@@ -420,11 +418,30 @@ static int lpuart_global_reset(struct lpuart_port *sport)
 	}
 
 	if (is_imx7ulp_lpuart(sport) || is_imx8qxp_lpuart(sport)) {
+		/*
+		 * If the transmitter is used by earlycon, wait transmit engin complete
+		 * and then reset
+		 */
+		tx_enable = lpuart32_read(port, UARTCTRL) & UARTCTRL_TE;
+		if (tx_enable) {
+			bd = lpuart32_read(&sport->port, UARTBAUD);
+			stat = lpuart32_read(port, UARTSTAT);
+			sfifo = lpuart32_read(port, UARTFIFO);
+			while (!(stat & UARTSTAT_TC && sfifo & UARTFIFO_TXEMPT))
+				cpu_relax();
+		}
+
 		global_addr = port->membase + UART_GLOBAL - IMX_REG_OFF;
 		writel(UART_GLOBAL_RST, global_addr);
 		usleep_range(GLOBAL_RST_MIN_US, GLOBAL_RST_MAX_US);
 		writel(0, global_addr);
 		usleep_range(GLOBAL_RST_MIN_US, GLOBAL_RST_MAX_US);
+
+		/* Recover the transmitter for earlycon */
+		if (tx_enable) {
+			lpuart32_write(port, bd, UARTBAUD);
+			lpuart32_write(port, UARTCTRL_TE, UARTCTRL);
+		}
 	}
 
 	clk_disable_unprepare(sport->ipg_clk);
-- 
2.17.1

Re: [PATCH] tty: serial: fsl_lpuart: don't break the on-going transfer when global reset

[Ilpo Järvinen]

On Wed, 19 Oct 2022, Sherry Sun wrote:

> lpuart_global_reset() shouldn't break the on-going transmit engin, need
> to recover the on-going data transfer after reset.
> 
> This can help earlycon here, since commit 60f361722ad2 ("serial:
> fsl_lpuart: Reset prior to registration") moved lpuart_global_reset()
> before uart_add_one_port(), earlycon is writing during global reset,
> as global reset will disable the TX and clear the baud rate register,
> which caused the earlycon cannot work any more after reset, needs to
> restore the baud rate and re-enable the transmitter to recover the
> earlycon write.
>
> Fixes: bd5305dcabbc ("tty: serial: fsl_lpuart: do software reset for imx7ulp and imx8qxp")
> Signed-off-by: Sherry Sun <sherry.sun@nxp.com>
> ---
>  drivers/tty/serial/fsl_lpuart.c | 23 ++++++++++++++++++++---
>  1 file changed, 20 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c
> index 67fa113f77d4..5064fdba1b61 100644
> --- a/drivers/tty/serial/fsl_lpuart.c
> +++ b/drivers/tty/serial/fsl_lpuart.c
> @@ -408,11 +408,9 @@ static int lpuart_global_reset(struct lpuart_port *sport)
>  {
>  	struct uart_port *port = &sport->port;
>  	void __iomem *global_addr;
> +	unsigned long tx_enable, bd, stat, sfifo;
>  	int ret;
>  
> -	if (uart_console(port))
> -		return 0;
> -
>  	ret = clk_prepare_enable(sport->ipg_clk);
>  	if (ret) {
>  		dev_err(sport->port.dev, "failed to enable uart ipg clk: %d\n", ret);
> @@ -420,11 +418,30 @@ static int lpuart_global_reset(struct lpuart_port *sport)
>  	}
>  
>  	if (is_imx7ulp_lpuart(sport) || is_imx8qxp_lpuart(sport)) {
> +		/*
> +		 * If the transmitter is used by earlycon, wait transmit engin complete
> +		 * and then reset
> +		 */
> +		tx_enable = lpuart32_read(port, UARTCTRL) & UARTCTRL_TE;
> +		if (tx_enable) {
> +			bd = lpuart32_read(&sport->port, UARTBAUD);
> +			stat = lpuart32_read(port, UARTSTAT);
> +			sfifo = lpuart32_read(port, UARTFIFO);
> +			while (!(stat & UARTSTAT_TC && sfifo & UARTFIFO_TXEMPT))
> +				cpu_relax();

This loop, if ever taken once, will loop forever as neither stat nor sfifo 
are reread inside the loop.

-- 
 i.

> +		}
> +
>  		global_addr = port->membase + UART_GLOBAL - IMX_REG_OFF;
>  		writel(UART_GLOBAL_RST, global_addr);
>  		usleep_range(GLOBAL_RST_MIN_US, GLOBAL_RST_MAX_US);
>  		writel(0, global_addr);
>  		usleep_range(GLOBAL_RST_MIN_US, GLOBAL_RST_MAX_US);
> +
> +		/* Recover the transmitter for earlycon */
> +		if (tx_enable) {
> +			lpuart32_write(port, bd, UARTBAUD);
> +			lpuart32_write(port, UARTCTRL_TE, UARTCTRL);
> +		}
>  	}
>  
>  	clk_disable_unprepare(sport->ipg_clk);
> 

RE: [PATCH] tty: serial: fsl_lpuart: don't break the on-going transfer when global reset

[Sherry Sun]

> -----Original Message-----
> From: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
> Sent: 2022年10月19日 17:20
> To: Sherry Sun <sherry.sun@nxp.com>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>; Jiri Slaby
> <jirislaby@kernel.org>; Lukas Wunner <lukas@wunner.de>; linux-serial
> <linux-serial@vger.kernel.org>; LKML <linux-kernel@vger.kernel.org>; dl-
> linux-imx <linux-imx@nxp.com>
> Subject: Re: [PATCH] tty: serial: fsl_lpuart: don't break the on-going transfer
> when global reset
> 
> On Wed, 19 Oct 2022, Sherry Sun wrote:
> 
> > lpuart_global_reset() shouldn't break the on-going transmit engin,
> > need to recover the on-going data transfer after reset.
> >
> > This can help earlycon here, since commit 60f361722ad2 ("serial:
> > fsl_lpuart: Reset prior to registration") moved lpuart_global_reset()
> > before uart_add_one_port(), earlycon is writing during global reset,
> > as global reset will disable the TX and clear the baud rate register,
> > which caused the earlycon cannot work any more after reset, needs to
> > restore the baud rate and re-enable the transmitter to recover the
> > earlycon write.
> >
> > Fixes: bd5305dcabbc ("tty: serial: fsl_lpuart: do software reset for
> > imx7ulp and imx8qxp")
> > Signed-off-by: Sherry Sun <sherry.sun@nxp.com>
> > ---
> >  drivers/tty/serial/fsl_lpuart.c | 23 ++++++++++++++++++++---
> >  1 file changed, 20 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/tty/serial/fsl_lpuart.c
> > b/drivers/tty/serial/fsl_lpuart.c index 67fa113f77d4..5064fdba1b61
> > 100644
> > --- a/drivers/tty/serial/fsl_lpuart.c
> > +++ b/drivers/tty/serial/fsl_lpuart.c
> > @@ -408,11 +408,9 @@ static int lpuart_global_reset(struct lpuart_port
> > *sport)  {
> >  	struct uart_port *port = &sport->port;
> >  	void __iomem *global_addr;
> > +	unsigned long tx_enable, bd, stat, sfifo;
> >  	int ret;
> >
> > -	if (uart_console(port))
> > -		return 0;
> > -
> >  	ret = clk_prepare_enable(sport->ipg_clk);
> >  	if (ret) {
> >  		dev_err(sport->port.dev, "failed to enable uart ipg clk: %d\n",
> > ret); @@ -420,11 +418,30 @@ static int lpuart_global_reset(struct
> lpuart_port *sport)
> >  	}
> >
> >  	if (is_imx7ulp_lpuart(sport) || is_imx8qxp_lpuart(sport)) {
> > +		/*
> > +		 * If the transmitter is used by earlycon, wait transmit engin
> complete
> > +		 * and then reset
> > +		 */
> > +		tx_enable = lpuart32_read(port, UARTCTRL) & UARTCTRL_TE;
> > +		if (tx_enable) {
> > +			bd = lpuart32_read(&sport->port, UARTBAUD);
> > +			stat = lpuart32_read(port, UARTSTAT);
> > +			sfifo = lpuart32_read(port, UARTFIFO);
> > +			while (!(stat & UARTSTAT_TC && sfifo &
> UARTFIFO_TXEMPT))
> > +				cpu_relax();
> 
> This loop, if ever taken once, will loop forever as neither stat nor sfifo are
> reread inside the loop.
> 
Hi Ilpo,

Good catch, you are right, will fix it in V2.

Best Regards
Sherry

> --
>  i.
> 
> > +		}
> > +
> >  		global_addr = port->membase + UART_GLOBAL -
> IMX_REG_OFF;
> >  		writel(UART_GLOBAL_RST, global_addr);
> >  		usleep_range(GLOBAL_RST_MIN_US, GLOBAL_RST_MAX_US);
> >  		writel(0, global_addr);
> >  		usleep_range(GLOBAL_RST_MIN_US, GLOBAL_RST_MAX_US);
> > +
> > +		/* Recover the transmitter for earlycon */
> > +		if (tx_enable) {
> > +			lpuart32_write(port, bd, UARTBAUD);
> > +			lpuart32_write(port, UARTCTRL_TE, UARTCTRL);
> > +		}
> >  	}
> >
> >  	clk_disable_unprepare(sport->ipg_clk);
> >