diff mbox series

[RFT,1/6] serial: sh-sci: Check if TX data was written to device in .tx_empty()

Message ID 20241204155806.3781200-2-claudiu.beznea.uj@bp.renesas.com
State New
Headers show
Series serial: sh-sci: Fixes for earlycon and keep_bootcon | expand

Commit Message

Claudiu Beznea Dec. 4, 2024, 3:58 p.m. UTC 
From: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>

On the Renesas RZ/G3S, when doing suspend to RAM, the uart_suspend_port()
is called. The uart_suspend_port() calls 3 times the
struct uart_port::ops::tx_empty() before shutting down the port.

According to the documentation, the struct uart_port::ops::tx_empty()
API tests whether the transmitter FIFO and shifter for the port is
empty.

The Renesas RZ/G3S SCIFA IP reports the number of data units stored in the
transmit FIFO through the FDR (FIFO Data Count Register). The data units
in the FIFOs are written in the shift register and transmitted from there.
The TEND bit in the Serial Status Register reports if the data was
transmitted from the shift register.

In the previous code, in the tx_empty() API implemented by the sh-sci
driver, it is considered that the TX is empty if the hardware reports the
TEND bit set and the number of data units in the FIFO is zero.

According to the HW manual, the TEND bit has the following meaning:

0: Transmission is in the waiting state or in progress.
1: Transmission is completed.

It has been noticed that when opening the serial device w/o using it and
then switch to a power saving mode, the tx_empty() call in the
uart_port_suspend() function fails, leading to the "Unable to drain
transmitter" message being printed on the console. This is because the
TEND=0 if nothing has been transmitted and the FIFOs are empty. As the
TEND=0 has double meaning (waiting state, in progress) we can't
determined the scenario described above.

Add a software workaround for this. This sets a variable if any data has
been sent on the serial console (when using PIO) or if the DMA callback has
been called (meaning something has been transmitted). In the tx_empty()
API the status of the DMA transaction is also checked and if it is
completed or in progress the code falls back in checking the hardware
registers instead of relying on the software variable.

Fixes: 73a19e4c0301 ("serial: sh-sci: Add DMA support.")
Cc: stable@vger.kernel.org
Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
---
 drivers/tty/serial/sh-sci.c | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

Comments

Geert Uytterhoeven Dec. 19, 2024, 9:46 a.m. UTC | #1 
Hi Claudiu,

On Wed, Dec 4, 2024 at 4:58 PM Claudiu <claudiu.beznea@tuxon.dev> wrote:
> From: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
>
> On the Renesas RZ/G3S, when doing suspend to RAM, the uart_suspend_port()
> is called. The uart_suspend_port() calls 3 times the
> struct uart_port::ops::tx_empty() before shutting down the port.
>
> According to the documentation, the struct uart_port::ops::tx_empty()
> API tests whether the transmitter FIFO and shifter for the port is
> empty.
>
> The Renesas RZ/G3S SCIFA IP reports the number of data units stored in the
> transmit FIFO through the FDR (FIFO Data Count Register). The data units
> in the FIFOs are written in the shift register and transmitted from there.
> The TEND bit in the Serial Status Register reports if the data was
> transmitted from the shift register.
>
> In the previous code, in the tx_empty() API implemented by the sh-sci
> driver, it is considered that the TX is empty if the hardware reports the
> TEND bit set and the number of data units in the FIFO is zero.
>
> According to the HW manual, the TEND bit has the following meaning:
>
> 0: Transmission is in the waiting state or in progress.
> 1: Transmission is completed.
>
> It has been noticed that when opening the serial device w/o using it and
> then switch to a power saving mode, the tx_empty() call in the
> uart_port_suspend() function fails, leading to the "Unable to drain
> transmitter" message being printed on the console. This is because the
> TEND=0 if nothing has been transmitted and the FIFOs are empty. As the
> TEND=0 has double meaning (waiting state, in progress) we can't
> determined the scenario described above.
>
> Add a software workaround for this. This sets a variable if any data has
> been sent on the serial console (when using PIO) or if the DMA callback has
> been called (meaning something has been transmitted). In the tx_empty()
> API the status of the DMA transaction is also checked and if it is
> completed or in progress the code falls back in checking the hardware
> registers instead of relying on the software variable.
>
> Fixes: 73a19e4c0301 ("serial: sh-sci: Add DMA support.")
> Cc: stable@vger.kernel.org
> Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>

Thanks for your patch, which is now commit 7cc0e0a43a910524 ("serial:
sh-sci: Check if TX data was written to device in .tx_empty()") in
v6.13-rc3.

> --- a/drivers/tty/serial/sh-sci.c
> +++ b/drivers/tty/serial/sh-sci.c
> @@ -885,6 +887,7 @@ static void sci_transmit_chars(struct uart_port *port)
>                 }
>
>                 sci_serial_out(port, SCxTDR, c);
> +               s->tx_occurred = true;

And you cannot use the existing port->icount.tx below, as that is not
reset to zero on sci_startup(), right?

>
>                 port->icount.tx++;

Which brings me to the real reason for replying to this patch:
apparently port->icount.tx is updated only for PIO, not for DMA...

>         } while (--count > 0);

> @@ -2247,6 +2275,7 @@ static int sci_startup(struct uart_port *port)
>
>         dev_dbg(port->dev, "%s(%d)\n", __func__, port->line);
>
> +       s->tx_occurred = false;
>         sci_request_dma(port);
>
>         ret = sci_request_irq(s);

Gr{oetje,eeting}s,

                        Geert
Claudiu Beznea Dec. 21, 2024, 9:16 a.m. UTC | #2 
Hi, Geert,

On 19.12.2024 11:46, Geert Uytterhoeven wrote:
> Hi Claudiu,
> 
> On Wed, Dec 4, 2024 at 4:58 PM Claudiu <claudiu.beznea@tuxon.dev> wrote:
>> From: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
>>
>> On the Renesas RZ/G3S, when doing suspend to RAM, the uart_suspend_port()
>> is called. The uart_suspend_port() calls 3 times the
>> struct uart_port::ops::tx_empty() before shutting down the port.
>>
>> According to the documentation, the struct uart_port::ops::tx_empty()
>> API tests whether the transmitter FIFO and shifter for the port is
>> empty.
>>
>> The Renesas RZ/G3S SCIFA IP reports the number of data units stored in the
>> transmit FIFO through the FDR (FIFO Data Count Register). The data units
>> in the FIFOs are written in the shift register and transmitted from there.
>> The TEND bit in the Serial Status Register reports if the data was
>> transmitted from the shift register.
>>
>> In the previous code, in the tx_empty() API implemented by the sh-sci
>> driver, it is considered that the TX is empty if the hardware reports the
>> TEND bit set and the number of data units in the FIFO is zero.
>>
>> According to the HW manual, the TEND bit has the following meaning:
>>
>> 0: Transmission is in the waiting state or in progress.
>> 1: Transmission is completed.
>>
>> It has been noticed that when opening the serial device w/o using it and
>> then switch to a power saving mode, the tx_empty() call in the
>> uart_port_suspend() function fails, leading to the "Unable to drain
>> transmitter" message being printed on the console. This is because the
>> TEND=0 if nothing has been transmitted and the FIFOs are empty. As the
>> TEND=0 has double meaning (waiting state, in progress) we can't
>> determined the scenario described above.
>>
>> Add a software workaround for this. This sets a variable if any data has
>> been sent on the serial console (when using PIO) or if the DMA callback has
>> been called (meaning something has been transmitted). In the tx_empty()
>> API the status of the DMA transaction is also checked and if it is
>> completed or in progress the code falls back in checking the hardware
>> registers instead of relying on the software variable.
>>
>> Fixes: 73a19e4c0301 ("serial: sh-sci: Add DMA support.")
>> Cc: stable@vger.kernel.org
>> Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
> Thanks for your patch, which is now commit 7cc0e0a43a910524 ("serial:
> sh-sci: Check if TX data was written to device in .tx_empty()") in
> v6.13-rc3.
> 
>> --- a/drivers/tty/serial/sh-sci.c
>> +++ b/drivers/tty/serial/sh-sci.c
>> @@ -885,6 +887,7 @@ static void sci_transmit_chars(struct uart_port *port)
>>                 }
>>
>>                 sci_serial_out(port, SCxTDR, c);
>> +               s->tx_occurred = true;
> And you cannot use the existing port->icount.tx below, as that is not
> reset to zero on sci_startup(), right?

I missed that the driver is incrementing the port->icount.tx . I'm not sure
we can use it though, as it is not reset on sci_startup(), as you pointed out.

Thank you,
Claudiu
diff mbox series

Patch

diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c
index df523c744423..924b803af440 100644
--- a/drivers/tty/serial/sh-sci.c
+++ b/drivers/tty/serial/sh-sci.c
@@ -157,6 +157,7 @@  struct sci_port {
 
 	bool has_rtscts;
 	bool autorts;
+	bool tx_occurred;
 };
 
 #define SCI_NPORTS CONFIG_SERIAL_SH_SCI_NR_UARTS
@@ -850,6 +851,7 @@  static void sci_transmit_chars(struct uart_port *port)
 {
 	struct tty_port *tport = &port->state->port;
 	unsigned int stopped = uart_tx_stopped(port);
+	struct sci_port *s = to_sci_port(port);
 	unsigned short status;
 	unsigned short ctrl;
 	int count;
@@ -885,6 +887,7 @@  static void sci_transmit_chars(struct uart_port *port)
 		}
 
 		sci_serial_out(port, SCxTDR, c);
+		s->tx_occurred = true;
 
 		port->icount.tx++;
 	} while (--count > 0);
@@ -1241,6 +1244,8 @@  static void sci_dma_tx_complete(void *arg)
 	if (kfifo_len(&tport->xmit_fifo) < WAKEUP_CHARS)
 		uart_write_wakeup(port);
 
+	s->tx_occurred = true;
+
 	if (!kfifo_is_empty(&tport->xmit_fifo)) {
 		s->cookie_tx = 0;
 		schedule_work(&s->work_tx);
@@ -1731,6 +1736,19 @@  static void sci_flush_buffer(struct uart_port *port)
 		s->cookie_tx = -EINVAL;
 	}
 }
+
+static void sci_dma_check_tx_occurred(struct sci_port *s)
+{
+	struct dma_tx_state state;
+	enum dma_status status;
+
+	if (!s->chan_tx)
+		return;
+
+	status = dmaengine_tx_status(s->chan_tx, s->cookie_tx, &state);
+	if (status == DMA_COMPLETE || status == DMA_IN_PROGRESS)
+		s->tx_occurred = true;
+}
 #else /* !CONFIG_SERIAL_SH_SCI_DMA */
 static inline void sci_request_dma(struct uart_port *port)
 {
@@ -1740,6 +1758,10 @@  static inline void sci_free_dma(struct uart_port *port)
 {
 }
 
+static void sci_dma_check_tx_occurred(struct sci_port *s)
+{
+}
+
 #define sci_flush_buffer	NULL
 #endif /* !CONFIG_SERIAL_SH_SCI_DMA */
 
@@ -2076,6 +2098,12 @@  static unsigned int sci_tx_empty(struct uart_port *port)
 {
 	unsigned short status = sci_serial_in(port, SCxSR);
 	unsigned short in_tx_fifo = sci_txfill(port);
+	struct sci_port *s = to_sci_port(port);
+
+	sci_dma_check_tx_occurred(s);
+
+	if (!s->tx_occurred)
+		return TIOCSER_TEMT;
 
 	return (status & SCxSR_TEND(port)) && !in_tx_fifo ? TIOCSER_TEMT : 0;
 }
@@ -2247,6 +2275,7 @@  static int sci_startup(struct uart_port *port)
 
 	dev_dbg(port->dev, "%s(%d)\n", __func__, port->line);
 
+	s->tx_occurred = false;
 	sci_request_dma(port);
 
 	ret = sci_request_irq(s);