2019-02-01 10:12:03

by Julien Masson

Subject: [PATCH] tty: serial: meson_uart: Add support for kernel debugger

The kgdb invokes the poll_put_char and poll_get_char when communicating
with the host. This patch implement the serial polling hooks for the
meson_uart to be used for KGDB debugging over serial line.

Signed-off-by: Julien Masson <[email protected]>
---
It has been tested on "Le Potato" board:
https://libre.computer/products/boards/aml-s905x-cc/

Kernel command line arguments:
kgdboc=ttyAML0,115200 kgdbretry=4 nokaslr kgdbcon

Kernel modules:
CONFIG_DEBUG_INFO=y
CONFIG_DEBUG_KERNEL=y
CONFIG_FRAME_POINTER=y
CONFIG_KGDB=y
CONFIG_KGDB_SERIAL_CONSOLE=y

Warning: for single step instruction I had to apply this patch:
https://lore.kernel.org/patchwork/patch/562423/

drivers/tty/serial/meson_uart.c | 46 +++++++++++++++++++++++++++++++++++++++++
1 file changed, 46 insertions(+)

diff --git a/drivers/tty/serial/meson_uart.c b/drivers/tty/serial/meson_uart.c
index 8a84259..49b20da 100644
--- a/drivers/tty/serial/meson_uart.c
+++ b/drivers/tty/serial/meson_uart.c
@@ -426,6 +426,48 @@ static void meson_uart_config_port(struct uart_port *port, int flags)
}
}

+#ifdef CONFIG_CONSOLE_POLL
+/*
+ * Console polling routines for writing and reading from the uart while
+ * in an interrupt or debug context (i.e. kgdb).
+ */
+
+static int meson_uart_poll_get_char(struct uart_port *port)
+{
+ u32 c;
+ unsigned long flags;
+
+ spin_lock_irqsave(&port->lock, flags);
+
+ if (readl(port->membase + AML_UART_STATUS) & AML_UART_RX_EMPTY)
+ c = NO_POLL_CHAR;
+ else
+ c = readl(port->membase + AML_UART_RFIFO);
+
+ spin_unlock_irqrestore(&port->lock, flags);
+
+ return c;
+}
+
+static void meson_uart_poll_put_char(struct uart_port *port, unsigned char c)
+{
+ unsigned long flags;
+
+ spin_lock_irqsave(&port->lock, flags);
+
+ while (!(readl(port->membase + AML_UART_STATUS) & AML_UART_TX_EMPTY))
+ cpu_relax();
+
+ writel(c, port->membase + AML_UART_WFIFO);
+
+ while (!(readl(port->membase + AML_UART_STATUS) & AML_UART_TX_EMPTY))
+ cpu_relax();
+
+ spin_unlock_irqrestore(&port->lock, flags);
+}
+
+#endif /* CONFIG_CONSOLE_POLL */
+
static const struct uart_ops meson_uart_ops = {
.set_mctrl = meson_uart_set_mctrl,
.get_mctrl = meson_uart_get_mctrl,
@@ -441,6 +483,10 @@ static const struct uart_ops meson_uart_ops = {
.request_port = meson_uart_request_port,
.release_port = meson_uart_release_port,
.verify_port = meson_uart_verify_port,
+#ifdef CONFIG_CONSOLE_POLL
+ .poll_get_char = meson_uart_poll_get_char,
+ .poll_put_char = meson_uart_poll_put_char,
+#endif
};

#ifdef CONFIG_SERIAL_MESON_CONSOLE
--
2.7.4

2019-02-01 10:20:19

by Corentin Labbe

Subject: Re: [PATCH] tty: serial: meson_uart: Add support for kernel debugger

On Fri, Feb 01, 2019 at 10:59:22AM +0100, Julien Masson wrote:
> The kgdb invokes the poll_put_char and poll_get_char when communicating
> with the host. This patch implement the serial polling hooks for the
> meson_uart to be used for KGDB debugging over serial line.
>
> Signed-off-by: Julien Masson <[email protected]>
> ---
> It has been tested on "Le Potato" board:
> https://libre.computer/products/boards/aml-s905x-cc/
>
> Kernel command line arguments:
> kgdboc=ttyAML0,115200 kgdbretry=4 nokaslr kgdbcon
>
> Kernel modules:
> CONFIG_DEBUG_INFO=y
> CONFIG_DEBUG_KERNEL=y
> CONFIG_FRAME_POINTER=y
> CONFIG_KGDB=y
> CONFIG_KGDB_SERIAL_CONSOLE=y
>
> Warning: for single step instruction I had to apply this patch:
> https://lore.kernel.org/patchwork/patch/562423/
>
> drivers/tty/serial/meson_uart.c | 46 +++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 46 insertions(+)
>
> diff --git a/drivers/tty/serial/meson_uart.c b/drivers/tty/serial/meson_uart.c
> index 8a84259..49b20da 100644
> --- a/drivers/tty/serial/meson_uart.c
> +++ b/drivers/tty/serial/meson_uart.c
> @@ -426,6 +426,48 @@ static void meson_uart_config_port(struct uart_port *port, int flags)
> }
> }
>
> +#ifdef CONFIG_CONSOLE_POLL
> +/*
> + * Console polling routines for writing and reading from the uart while
> + * in an interrupt or debug context (i.e. kgdb).
> + */
> +
> +static int meson_uart_poll_get_char(struct uart_port *port)
> +{
> + u32 c;
> + unsigned long flags;
> +
> + spin_lock_irqsave(&port->lock, flags);
> +
> + if (readl(port->membase + AML_UART_STATUS) & AML_UART_RX_EMPTY)
> + c = NO_POLL_CHAR;
> + else
> + c = readl(port->membase + AML_UART_RFIFO);
> +
> + spin_unlock_irqrestore(&port->lock, flags);
> +
> + return c;
> +}
> +
> +static void meson_uart_poll_put_char(struct uart_port *port, unsigned char c)
> +{
> + unsigned long flags;
> +
> + spin_lock_irqsave(&port->lock, flags);
> +
> + while (!(readl(port->membase + AML_UART_STATUS) & AML_UART_TX_EMPTY))
> + cpu_relax();

Hello

Perhaps you could use read_poll_timeout() ?
This will also permit to handle the timeout case.

Regards

2019-02-07 17:06:30

by Julien Masson

Subject: Re: [PATCH] tty: serial: meson_uart: Add support for kernel debugger

On Fri 01 Feb 2019 at 11:10, Corentin Labbe <[email protected]> wrote:

> On Fri, Feb 01, 2019 at 10:59:22AM +0100, Julien Masson wrote:
>> The kgdb invokes the poll_put_char and poll_get_char when communicating
>> with the host. This patch implement the serial polling hooks for the
>> meson_uart to be used for KGDB debugging over serial line.
>>
>> Signed-off-by: Julien Masson <[email protected]>
>> ---
>> It has been tested on "Le Potato" board:
>> https://libre.computer/products/boards/aml-s905x-cc/
>>
>> Kernel command line arguments:
>> kgdboc=ttyAML0,115200 kgdbretry=4 nokaslr kgdbcon
>>
>> Kernel modules:
>> CONFIG_DEBUG_INFO=y
>> CONFIG_DEBUG_KERNEL=y
>> CONFIG_FRAME_POINTER=y
>> CONFIG_KGDB=y
>> CONFIG_KGDB_SERIAL_CONSOLE=y
>>
>> Warning: for single step instruction I had to apply this patch:
>> https://lore.kernel.org/patchwork/patch/562423/
>>
>> drivers/tty/serial/meson_uart.c | 46 +++++++++++++++++++++++++++++++++++++++++
>> 1 file changed, 46 insertions(+)
>>
>> diff --git a/drivers/tty/serial/meson_uart.c b/drivers/tty/serial/meson_uart.c
>> index 8a84259..49b20da 100644
>> --- a/drivers/tty/serial/meson_uart.c
>> +++ b/drivers/tty/serial/meson_uart.c
>> @@ -426,6 +426,48 @@ static void meson_uart_config_port(struct uart_port *port, int flags)
>> }
>> }
>>
>> +#ifdef CONFIG_CONSOLE_POLL
>> +/*
>> + * Console polling routines for writing and reading from the uart while
>> + * in an interrupt or debug context (i.e. kgdb).
>> + */
>> +
>> +static int meson_uart_poll_get_char(struct uart_port *port)
>> +{
>> + u32 c;
>> + unsigned long flags;
>> +
>> + spin_lock_irqsave(&port->lock, flags);
>> +
>> + if (readl(port->membase + AML_UART_STATUS) & AML_UART_RX_EMPTY)
>> + c = NO_POLL_CHAR;
>> + else
>> + c = readl(port->membase + AML_UART_RFIFO);
>> +
>> + spin_unlock_irqrestore(&port->lock, flags);
>> +
>> + return c;
>> +}
>> +
>> +static void meson_uart_poll_put_char(struct uart_port *port, unsigned char c)
>> +{
>> + unsigned long flags;
>> +
>> + spin_lock_irqsave(&port->lock, flags);
>> +
>> + while (!(readl(port->membase + AML_UART_STATUS) & AML_UART_TX_EMPTY))
>> + cpu_relax();
>
> Hello
>
> Perhaps you could use read_poll_timeout() ?
> This will also permit to handle the timeout case.
>
> Regards

Thanks for the tips Corentin.

I tested with a poll of 5 usec and 1 msec of timeout.
I had to use readl_poll_timeout_atomic(...) since I'm in atomic context
(spinlock).

I'll send a v2 of this patch.

Regards