linux-kernel - [PATCH v2] tty: serial: uartlite: Specify time for sending chars

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Message-Id: <f5c4b014d747ea39928d940a579cb4e44d6bbd9a.1399351570.git.michal.simek@xilinx.com>
Date:	Tue,  6 May 2014 06:46:15 +0200
From:	Michal Simek <michal.simek@...inx.com>
To:	linux-kernel@...r.kernel.org
Cc:	Michal Simek <monstr@...str.eu>,
	Michal Simek <michal.simek@...inx.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-serial@...r.kernel.org, arnd@...db.de,
	Peter Korsgaard <jacmet@...site.dk>,
	Grant Likely <grant.likely@...retlab.ca>,
	Rob Herring <rob.herring@...xeda.com>,
	Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH v2] tty: serial: uartlite: Specify time for sending chars

Xilinx MDM (Microblaze Debug Module) also contains
uart interface via JTAG which is compatible with
uartlite driver. This interface is really slow
that's why timeout is setup to 1s.

Make this time delay not to be cpu speed dependent.

Signed-off-by: Michal Simek <michal.simek@...inx.com>
Acked-by: Peter Korsgaard <peter@...sgaard.com>
---

Changes in v2:
- Add Peter's ACK
- Extend commentary

RFC sent here:
https://lkml.org/lkml/2013/9/30/250
I finally got HW design which is just slow to be able
to test it.

---
 drivers/tty/serial/uartlite.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/drivers/tty/serial/uartlite.c b/drivers/tty/serial/uartlite.c
index 5f90ef24d475..dce27f34937e 100644
--- a/drivers/tty/serial/uartlite.c
+++ b/drivers/tty/serial/uartlite.c
@@ -418,14 +418,23 @@ static struct uart_ops ulite_ops = {
 #ifdef CONFIG_SERIAL_UARTLITE_CONSOLE
 static void ulite_console_wait_tx(struct uart_port *port)
 {
-	int i;
 	u8 val;
-
-	/* Spin waiting for TX fifo to have space available */
-	for (i = 0; i < 100000; i++) {
+	unsigned long timeout;
+
+	/*
+	 * Spin waiting for TX fifo to have space available.
+	 * When using the Microblaze Debug Module this can take up to 1s
+	 */
+	timeout = jiffies + msecs_to_jiffies(1000);
+	while (1) {
 		val = uart_in32(ULITE_STATUS, port);
 		if ((val & ULITE_STATUS_TXFULL) == 0)
 			break;
+		if (time_after(jiffies, timeout)) {
+			dev_warn(port->dev,
+				 "timeout waiting for TX buffer empty\n");
+			break;
+		}
 		cpu_relax();
 	}
 }
--
1.8.2.3


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