[PATCH] serial: sprd: Add polling IO support

[PATCH] serial: sprd: Add polling IO support

[Lanqing Liu]

In order to access the UART without the interrupts, the kernel uses
the basic polling methods for IO with the device. With these methods
implemented, it is now possible to enable kgdb during early boot over serial.

Signed-off-by: Lanqing Liu <liuhhome@gmail.com>
---
 drivers/tty/serial/sprd_serial.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/drivers/tty/serial/sprd_serial.c b/drivers/tty/serial/sprd_serial.c
index 73d71a4..579ab41 100644
--- a/drivers/tty/serial/sprd_serial.c
+++ b/drivers/tty/serial/sprd_serial.c
@@ -911,6 +911,24 @@ static void sprd_pm(struct uart_port *port, unsigned int state,
 	}
 }
 
+#ifdef CONFIG_CONSOLE_POLL
+static int sprd_poll_get_char(struct uart_port *port)
+{
+	while (!(serial_in(port, SPRD_STS1) & SPRD_RX_FIFO_CNT_MASK))
+		cpu_relax();
+
+	return serial_in(port, SPRD_RXD);
+}
+
+static void sprd_poll_put_char(struct uart_port *port, unsigned char ch)
+{
+	while (serial_in(port, SPRD_STS1) & SPRD_TX_FIFO_CNT_MASK)
+		cpu_relax();
+
+	serial_out(port, SPRD_TXD, ch);
+}
+#endif
+
 static const struct uart_ops serial_sprd_ops = {
 	.tx_empty = sprd_tx_empty,
 	.get_mctrl = sprd_get_mctrl,
@@ -928,6 +946,10 @@ static void sprd_pm(struct uart_port *port, unsigned int state,
 	.config_port = sprd_config_port,
 	.verify_port = sprd_verify_port,
 	.pm = sprd_pm,
+#ifdef CONFIG_CONSOLE_POLL
+	.poll_get_char	= sprd_poll_get_char,
+	.poll_put_char	= sprd_poll_put_char,
+#endif
 };
 
 #ifdef CONFIG_SERIAL_SPRD_CONSOLE
-- 
1.9.1

Re: [PATCH] serial: sprd: Add polling IO support

[Baolin Wang]

Hi Lanqing,

On Wed, 18 Sep 2019 at 16:16, Lanqing Liu <liuhhome@gmail.com> wrote:
>
> In order to access the UART without the interrupts, the kernel uses
> the basic polling methods for IO with the device. With these methods
> implemented, it is now possible to enable kgdb during early boot over serial.
>
> Signed-off-by: Lanqing Liu <liuhhome@gmail.com>
> ---
>  drivers/tty/serial/sprd_serial.c | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
>
> diff --git a/drivers/tty/serial/sprd_serial.c b/drivers/tty/serial/sprd_serial.c
> index 73d71a4..579ab41 100644
> --- a/drivers/tty/serial/sprd_serial.c
> +++ b/drivers/tty/serial/sprd_serial.c
> @@ -911,6 +911,24 @@ static void sprd_pm(struct uart_port *port, unsigned int state,
>         }
>  }
>
> +#ifdef CONFIG_CONSOLE_POLL
> +static int sprd_poll_get_char(struct uart_port *port)
> +{
> +       while (!(serial_in(port, SPRD_STS1) & SPRD_RX_FIFO_CNT_MASK))
> +               cpu_relax();
> +
> +       return serial_in(port, SPRD_RXD);
> +}
> +
> +static void sprd_poll_put_char(struct uart_port *port, unsigned char ch)
> +{
> +       while (serial_in(port, SPRD_STS1) & SPRD_TX_FIFO_CNT_MASK)
> +               cpu_relax();
> +
> +       serial_out(port, SPRD_TXD, ch);
> +}
> +#endif

When I tested your patch, I found only one case can work if the port
used by KGDB is same with the port selected as console, which means
this port will be powered on all the time. We had implemented the
power management for the UART ports, so I think you should enable the
clock for the port used by KGDB in poll_init(), then other ports can
be used by KGDB.

> +
>  static const struct uart_ops serial_sprd_ops = {
>         .tx_empty = sprd_tx_empty,
>         .get_mctrl = sprd_get_mctrl,
> @@ -928,6 +946,10 @@ static void sprd_pm(struct uart_port *port, unsigned int state,
>         .config_port = sprd_config_port,
>         .verify_port = sprd_verify_port,
>         .pm = sprd_pm,
> +#ifdef CONFIG_CONSOLE_POLL
> +       .poll_get_char  = sprd_poll_get_char,
> +       .poll_put_char  = sprd_poll_put_char,
> +#endif
>  };
>
>  #ifdef CONFIG_SERIAL_SPRD_CONSOLE
> --
> 1.9.1
>


-- 
Baolin Wang
Best Regards

Re: [PATCH] serial: sprd: Add polling IO support

[hhome liu]

Baolin Wang <baolin.wang@linaro.org> 于2019年9月18日周三 下午8:10写道：
>
> Hi Lanqing,
>
> On Wed, 18 Sep 2019 at 16:16, Lanqing Liu <liuhhome@gmail.com> wrote:
> >
> > In order to access the UART without the interrupts, the kernel uses
> > the basic polling methods for IO with the device. With these methods
> > implemented, it is now possible to enable kgdb during early boot over serial.
> >
> > Signed-off-by: Lanqing Liu <liuhhome@gmail.com>
> > ---
> >  drivers/tty/serial/sprd_serial.c | 22 ++++++++++++++++++++++
> >  1 file changed, 22 insertions(+)
> >
> > diff --git a/drivers/tty/serial/sprd_serial.c b/drivers/tty/serial/sprd_serial.c
> > index 73d71a4..579ab41 100644
> > --- a/drivers/tty/serial/sprd_serial.c
> > +++ b/drivers/tty/serial/sprd_serial.c
> > @@ -911,6 +911,24 @@ static void sprd_pm(struct uart_port *port, unsigned int state,
> >         }
> >  }
> >
> > +#ifdef CONFIG_CONSOLE_POLL
> > +static int sprd_poll_get_char(struct uart_port *port)
> > +{
> > +       while (!(serial_in(port, SPRD_STS1) & SPRD_RX_FIFO_CNT_MASK))
> > +               cpu_relax();
> > +
> > +       return serial_in(port, SPRD_RXD);
> > +}
> > +
> > +static void sprd_poll_put_char(struct uart_port *port, unsigned char ch)
> > +{
> > +       while (serial_in(port, SPRD_STS1) & SPRD_TX_FIFO_CNT_MASK)
> > +               cpu_relax();
> > +
> > +       serial_out(port, SPRD_TXD, ch);
> > +}
> > +#endif
>
> When I tested your patch, I found only one case can work if the port
> used by KGDB is same with the port selected as console, which means
> this port will be powered on all the time. We had implemented the
> power management for the UART ports, so I think you should enable the
> clock for the port used by KGDB in poll_init(), then other ports can
> be used by KGDB.
>
Yes, agree with you. I will add poll_init()  support.  Thanks for your
comments.
> > +
> >  static const struct uart_ops serial_sprd_ops = {
> >         .tx_empty = sprd_tx_empty,
> >         .get_mctrl = sprd_get_mctrl,
> > @@ -928,6 +946,10 @@ static void sprd_pm(struct uart_port *port, unsigned int state,
> >         .config_port = sprd_config_port,
> >         .verify_port = sprd_verify_port,
> >         .pm = sprd_pm,
> > +#ifdef CONFIG_CONSOLE_POLL
> > +       .poll_get_char  = sprd_poll_get_char,
> > +       .poll_put_char  = sprd_poll_put_char,
> > +#endif
> >  };
> >
> >  #ifdef CONFIG_SERIAL_SPRD_CONSOLE
> > --
> > 1.9.1
> >
>
>
> --
> Baolin Wang
> Best Regards