Re: [PATCH] atmel_serial: Split the interrupt handler

["Remy Bohmer" <linux@bohmer.net>]

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Hello Haavard,

A few remarks:

> From: Remy Bohmer <hskinnemoen@atmel.com>

My name, at your address ;-)))

> This patch splits up the interrupt handler of the serial port
> into a interrupt top-half and a tasklet.

I see you moved the handling of the sysrq-key to the tasklet. This was
actually a very nice feature in the IRQ-top half on preempt-RT. This
helps debugging running away RT-processes.

> In this version of the patch, we try to only do things that are
> absolutely necessary in the interrupt handler, storing away the
> status register along with the received character and letting the
> tasklet handle break, sysrq, error flags, etc.

Preempt-RT now absolutely requires my (4th) IRQ_NODELAY patch, because
the spinlock now is always inside the code, and not only in
theexception path, and thus without my NO_DELAY patch we have a panic
during boot.
On preempt-RT this spinlock must be a raw-spinlock. (If this type is
known in the mainline kernel, you can apply that patch it anyway)

BTW: Attached I have added a 2nd patch that I use for Preempt-RT. (For
cleaner startup, and to get rid of useless IRQ-threads.

> This patch should apply on top of the cleanup patch I sent earlier

For the cleanup patch:
Acked-by: Remy Bohmer <linux@bohmer.net>

> today. Or at least I think so...I'll send the full series once
> everyone are happy.

So, for this patch: I am almost happy ;-)


Kind Regards,

Remy

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This patch prevents starting up a useless IRQ-thread for IRQ-1,
because this IRQ is running in IRQF_NODELAY context due to the 
timer interrupt.

Signed-off-by: Remy Bohmer <linux@bohmer.net>
---
 drivers/serial/atmel_serial.c |   10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

Index: linux-2.6.23/drivers/serial/atmel_serial.c
===================================================================
--- linux-2.6.23.orig/drivers/serial/atmel_serial.c	2007-12-18 15:49:02.000000000 +0100
+++ linux-2.6.23/drivers/serial/atmel_serial.c	2007-12-18 15:56:37.000000000 +0100
@@ -549,6 +549,7 @@ static int atmel_startup(struct uart_por
 {
 	struct atmel_uart_port *atmel_port = (struct atmel_uart_port *) port;
 	int retval;
+	unsigned long irqflags = IRQF_SHARED;
 
 	/*
 	 * Ensure that no interrupts are enabled otherwise when
@@ -557,10 +558,17 @@ static int atmel_startup(struct uart_por
 	 */
 	UART_PUT_IDR(port, -1);
 
+#ifdef CONFIG_PREEMPT_RT
+	/* IRQ1 is the System IRQ, which is shared with the Timer-IRQ, and
+	   thus it is running in IRQF_NODELAY context. By setting this flag
+	   here also, we prevent starting up a useless IRQ-thread.*/
+	if (port->irq == 1)
+		irqflags |= IRQF_NODELAY;
+#endif
 	/*
 	 * Allocate the IRQ
 	 */
-	retval = request_irq(port->irq, atmel_interrupt, IRQF_SHARED,
+	retval = request_irq(port->irq, atmel_interrupt, irqflags,
 			"atmel_serial", port);
 	if (retval) {
 		printk("atmel_serial: atmel_startup - Can't get irq\n");