On Fri 01 Feb 2019 at 11:10, Corentin Labbe [off-list ref] wrote:

On Fri, Feb 01, 2019 at 10:59:22AM +0100, Julien Masson wrote:

quoted

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 <redacted>
---
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

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel