[PATCH V2 0/3] serial: stm32: add earlycon and polling mode

[PATCH V2 0/3] serial: stm32: add earlycon and polling mode

[Valentin Caron]

- Add support of early console and polling mode in stm32-usart driver.
- Avoid a possible infinite loop in putchar function.

Changes since v1:
- Fix warning "unused variable 'ret'"

Valentin Caron (3):
  serial: stm32: remove infinite loop possibility in putchar function
  serial: stm32: add KGDB support
  serial: stm32: add earlycon support

 .../admin-guide/kernel-parameters.txt         |   6 ++
 drivers/tty/serial/Kconfig                    |   1 +
 drivers/tty/serial/stm32-usart.c              | 100 +++++++++++++++++-
 drivers/tty/serial/stm32-usart.h              |   2 +
 4 files changed, 104 insertions(+), 5 deletions(-)

-- 
2.25.1

[PATCH V2 1/3] serial: stm32: remove infinite loop possibility in putchar function

[Valentin Caron]

Rework stm32_usart_console_putchar() function in order to anticipate
the case where the character can never be sent.

Signed-off-by: Valentin Caron <valentin.caron@foss.st.com>
---
 drivers/tty/serial/stm32-usart.c | 12 +++++++++---
 drivers/tty/serial/stm32-usart.h |  2 ++
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index 87b5cd4c9743..83895da84891 100644
--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -1645,10 +1645,16 @@ static void stm32_usart_console_putchar(struct uart_port *port, unsigned char ch
 {
 	struct stm32_port *stm32_port = to_stm32_port(port);
 	const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;
+	u32 isr;
+	int ret;
 
-	while (!(readl_relaxed(port->membase + ofs->isr) & USART_SR_TXE))
-		cpu_relax();
-
+	ret = readl_relaxed_poll_timeout_atomic(port->membase + ofs->isr, isr,
+						(isr & USART_SR_TXE), 100,
+						STM32_USART_TIMEOUT_USEC);
+	if (ret != 0) {
+		dev_err(port->dev, "Error while sending data in UART TX : %d\n", ret);
+		return;
+	}
 	writel_relaxed(ch, port->membase + ofs->tdr);
 }
 
diff --git a/drivers/tty/serial/stm32-usart.h b/drivers/tty/serial/stm32-usart.h
index feab952aec16..d734c4a5fd24 100644
--- a/drivers/tty/serial/stm32-usart.h
+++ b/drivers/tty/serial/stm32-usart.h
@@ -251,6 +251,8 @@ struct stm32_usart_info stm32h7_info = {
 #define RX_BUF_P (RX_BUF_L / 2)	 /* dma rx buffer period     */
 #define TX_BUF_L RX_BUF_L	 /* dma tx buffer length     */
 
+#define STM32_USART_TIMEOUT_USEC USEC_PER_SEC /* 1s timeout in µs */
+
 struct stm32_port {
 	struct uart_port port;
 	struct clk *clk;
-- 
2.25.1

[PATCH V2 2/3] serial: stm32: add KGDB support

[Valentin Caron]

Add support for KGDB in stm32 serial driver by implementing characters
polling callbacks (poll_init, poll_get_char and poll_put_char).

Signed-off-by: Erwan Le Ray <erwan.leray@foss.st.com>
Signed-off-by: Jean Philippe Romain <jean-philippe.romain@foss.st.com>
Signed-off-by: Valentin Caron <valentin.caron@foss.st.com>
---
 drivers/tty/serial/stm32-usart.c | 37 ++++++++++++++++++++++++++++++--
 1 file changed, 35 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index 83895da84891..4307c822afe4 100644
--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -37,6 +37,7 @@
 
 static void stm32_usart_stop_tx(struct uart_port *port);
 static void stm32_usart_transmit_chars(struct uart_port *port);
+static void __maybe_unused stm32_usart_console_putchar(struct uart_port *port, unsigned char ch);
 
 static inline struct stm32_port *to_stm32_port(struct uart_port *port)
 {
@@ -1222,6 +1223,33 @@ static void stm32_usart_pm(struct uart_port *port, unsigned int state,
 	}
 }
 
+#if defined(CONFIG_CONSOLE_POLL)
+
+ /* Callbacks for characters polling in debug context (i.e. KGDB). */
+static int stm32_usart_poll_init(struct uart_port *port)
+{
+	struct stm32_port *stm32_port = to_stm32_port(port);
+
+	return clk_prepare_enable(stm32_port->clk);
+}
+
+static int stm32_usart_poll_get_char(struct uart_port *port)
+{
+	struct stm32_port *stm32_port = to_stm32_port(port);
+	const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;
+
+	if (!(readl_relaxed(port->membase + ofs->isr) & USART_SR_RXNE))
+		return NO_POLL_CHAR;
+
+	return readl_relaxed(port->membase + ofs->rdr) & stm32_port->rdr_mask;
+}
+
+static void stm32_usart_poll_put_char(struct uart_port *port, unsigned char ch)
+{
+	stm32_usart_console_putchar(port, ch);
+}
+#endif /* CONFIG_CONSOLE_POLL */
+
 static const struct uart_ops stm32_uart_ops = {
 	.tx_empty	= stm32_usart_tx_empty,
 	.set_mctrl	= stm32_usart_set_mctrl,
@@ -1243,6 +1271,11 @@ static const struct uart_ops stm32_uart_ops = {
 	.request_port	= stm32_usart_request_port,
 	.config_port	= stm32_usart_config_port,
 	.verify_port	= stm32_usart_verify_port,
+#if defined(CONFIG_CONSOLE_POLL)
+	.poll_init      = stm32_usart_poll_init,
+	.poll_get_char	= stm32_usart_poll_get_char,
+	.poll_put_char	= stm32_usart_poll_put_char,
+#endif /* CONFIG_CONSOLE_POLL */
 };
 
 /*
@@ -1640,8 +1673,7 @@ static int stm32_usart_serial_remove(struct platform_device *pdev)
 	return 0;
 }
 
-#ifdef CONFIG_SERIAL_STM32_CONSOLE
-static void stm32_usart_console_putchar(struct uart_port *port, unsigned char ch)
+static void __maybe_unused stm32_usart_console_putchar(struct uart_port *port, unsigned char ch)
 {
 	struct stm32_port *stm32_port = to_stm32_port(port);
 	const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;
@@ -1658,6 +1690,7 @@ static void stm32_usart_console_putchar(struct uart_port *port, unsigned char ch
 	writel_relaxed(ch, port->membase + ofs->tdr);
 }
 
+#ifdef CONFIG_SERIAL_STM32_CONSOLE
 static void stm32_usart_console_write(struct console *co, const char *s,
 				      unsigned int cnt)
 {
-- 
2.25.1

[PATCH V2 3/3] serial: stm32: add earlycon support

[Valentin Caron]

Add early console support in stm32 uart driver.

Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>
Signed-off-by: Valentin Caron <valentin.caron@foss.st.com>
---
 .../admin-guide/kernel-parameters.txt         |  6 +++
 drivers/tty/serial/Kconfig                    |  1 +
 drivers/tty/serial/stm32-usart.c              | 51 +++++++++++++++++++
 3 files changed, 58 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 3f1cc5e317ed..e941c3351c7a 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1264,6 +1264,12 @@
 			address must be provided, and the serial port must
 			already be setup and configured.
 
+		stm32,<addr>
+			Use early console provided by ST Microelectronics
+			serial driver for STM32 SoCs. A valid base address
+			must be provided, and the serial port must already
+			be setup and configured.
+
 	earlyprintk=	[X86,SH,ARM,M68k,S390]
 			earlyprintk=vga
 			earlyprintk=sclp
diff --git a/drivers/tty/serial/Kconfig b/drivers/tty/serial/Kconfig
index 6949e883ffab..ed59de8d2e11 100644
--- a/drivers/tty/serial/Kconfig
+++ b/drivers/tty/serial/Kconfig
@@ -1443,6 +1443,7 @@ config SERIAL_STM32_CONSOLE
 	bool "Support for console on STM32"
 	depends on SERIAL_STM32=y
 	select SERIAL_CORE_CONSOLE
+	select SERIAL_EARLYCON
 
 config SERIAL_MVEBU_UART
 	bool "Marvell EBU serial port support"
diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index 4307c822afe4..65988e6efaa2 100644
--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -1766,6 +1766,57 @@ static struct console stm32_console = {
 #define STM32_SERIAL_CONSOLE NULL
 #endif /* CONFIG_SERIAL_STM32_CONSOLE */
 
+#ifdef CONFIG_SERIAL_EARLYCON
+static void early_stm32_usart_console_putchar(struct uart_port *port, unsigned char ch)
+{
+	struct stm32_usart_info *info = port->private_data;
+
+	while (!(readl_relaxed(port->membase + info->ofs.isr) & USART_SR_TXE))
+		cpu_relax();
+
+	writel_relaxed(ch, port->membase + info->ofs.tdr);
+}
+
+static void early_stm32_serial_write(struct console *console, const char *s, unsigned int count)
+{
+	struct earlycon_device *device = console->data;
+	struct uart_port *port = &device->port;
+
+	uart_console_write(port, s, count, early_stm32_usart_console_putchar);
+}
+
+static int __init early_stm32_h7_serial_setup(struct earlycon_device *device, const char *options)
+{
+	if (!(device->port.membase || device->port.iobase))
+		return -ENODEV;
+	device->port.private_data = &stm32h7_info;
+	device->con->write = early_stm32_serial_write;
+	return 0;
+}
+
+static int __init early_stm32_f7_serial_setup(struct earlycon_device *device, const char *options)
+{
+	if (!(device->port.membase || device->port.iobase))
+		return -ENODEV;
+	device->port.private_data = &stm32f7_info;
+	device->con->write = early_stm32_serial_write;
+	return 0;
+}
+
+static int __init early_stm32_f4_serial_setup(struct earlycon_device *device, const char *options)
+{
+	if (!(device->port.membase || device->port.iobase))
+		return -ENODEV;
+	device->port.private_data = &stm32f4_info;
+	device->con->write = early_stm32_serial_write;
+	return 0;
+}
+
+OF_EARLYCON_DECLARE(stm32, "st,stm32h7-uart", early_stm32_h7_serial_setup);
+OF_EARLYCON_DECLARE(stm32, "st,stm32f7-uart", early_stm32_f7_serial_setup);
+OF_EARLYCON_DECLARE(stm32, "st,stm32-uart", early_stm32_f4_serial_setup);
+#endif /* CONFIG_SERIAL_EARLYCON */
+
 static struct uart_driver stm32_usart_driver = {
 	.driver_name	= DRIVER_NAME,
 	.dev_name	= STM32_SERIAL_NAME,
-- 
2.25.1

Re: [PATCH V2 3/3] serial: stm32: add earlycon support

[Geert Uytterhoeven]

Hi Valentin,

On Fri, Apr 8, 2022 at 3:14 PM Valentin Caron
<valentin.caron@foss.st.com> wrote:
> Add early console support in stm32 uart driver.
>
> Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>
> Signed-off-by: Valentin Caron <valentin.caron@foss.st.com>

Thanks for your patch!

> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -1264,6 +1264,12 @@
>                         address must be provided, and the serial port must
>                         already be setup and configured.
>
> +               stm32,<addr>
> +                       Use early console provided by ST Microelectronics
> +                       serial driver for STM32 SoCs. A valid base address
> +                       must be provided, and the serial port must already
> +                       be setup and configured.

Why do you need this parameter?

Given this driver uses DT, can't it figure out the serial port address
from chosen/stdout-path?

+OF_EARLYCON_DECLARE(stm32, "st,stm32h7-uart", early_stm32_h7_serial_setup);
+OF_EARLYCON_DECLARE(stm32, "st,stm32f7-uart", early_stm32_f7_serial_setup);
+OF_EARLYCON_DECLARE(stm32, "st,stm32-uart", early_stm32_f4_serial_setup);

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Re: [PATCH V2 3/3] serial: stm32: add earlycon support

[Valentin CARON]

On 4/11/22 16:59, Geert Uytterhoeven wrote:
> Hi Valentin,
>
> On Fri, Apr 8, 2022 at 3:14 PM Valentin Caron
> <valentin.caron@foss.st.com> wrote:
>> Add early console support in stm32 uart driver.
>>
>> Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>
>> Signed-off-by: Valentin Caron <valentin.caron@foss.st.com>
> Thanks for your patch!
>
>> --- a/Documentation/admin-guide/kernel-parameters.txt
>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>> @@ -1264,6 +1264,12 @@
>>                          address must be provided, and the serial port must
>>                          already be setup and configured.
>>
>> +               stm32,<addr>
>> +                       Use early console provided by ST Microelectronics
>> +                       serial driver for STM32 SoCs. A valid base address
>> +                       must be provided, and the serial port must already
>> +                       be setup and configured.
> Why do you need this parameter?
>
> Given this driver uses DT, can't it figure out the serial port address
> from chosen/stdout-path?
>
> +OF_EARLYCON_DECLARE(stm32, "st,stm32h7-uart", early_stm32_h7_serial_setup);
> +OF_EARLYCON_DECLARE(stm32, "st,stm32f7-uart", early_stm32_f7_serial_setup);
> +OF_EARLYCON_DECLARE(stm32, "st,stm32-uart", early_stm32_f4_serial_setup);
>
> Gr{oetje,eeting}s,
>
>                          Geert
>
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
>
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
>                                  -- Linus Torvalds

Hi Geert,

I took the example of other serial drivers.
Both methods work (with earlycon/stdout-path and with 
earlycon=stm32,0xXXXXXXX)
but your right, the second will probably never used on this driver.

Should I remove it ?

Thanks,
Valentin

Re: [PATCH V2 3/3] serial: stm32: add earlycon support

[Geert Uytterhoeven]

Hi Valentin,

On Thu, Apr 14, 2022 at 2:17 PM Valentin CARON
<valentin.caron@foss.st.com> wrote:
> On 4/11/22 16:59, Geert Uytterhoeven wrote:
> > On Fri, Apr 8, 2022 at 3:14 PM Valentin Caron
> > <valentin.caron@foss.st.com> wrote:
> >> Add early console support in stm32 uart driver.
> >>
> >> Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>
> >> Signed-off-by: Valentin Caron <valentin.caron@foss.st.com>
> > Thanks for your patch!
> >
> >> --- a/Documentation/admin-guide/kernel-parameters.txt
> >> +++ b/Documentation/admin-guide/kernel-parameters.txt
> >> @@ -1264,6 +1264,12 @@
> >>                          address must be provided, and the serial port must
> >>                          already be setup and configured.
> >>
> >> +               stm32,<addr>
> >> +                       Use early console provided by ST Microelectronics
> >> +                       serial driver for STM32 SoCs. A valid base address
> >> +                       must be provided, and the serial port must already
> >> +                       be setup and configured.
> > Why do you need this parameter?
> >
> > Given this driver uses DT, can't it figure out the serial port address
> > from chosen/stdout-path?
>
> I took the example of other serial drivers.
> Both methods work (with earlycon/stdout-path and with
> earlycon=stm32,0xXXXXXXX)
> but your right, the second will probably never used on this driver.
>
> Should I remove it ?

I think you should.  The less platform-specific kernel parameters,
the better. And the less bad examples to copy from.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds