* Frans Klaver | 2014-09-08 16:46:18 [+0200]:
>- ncurses based applications (vi, less) don't play nice for me on the
> console with this series. less doesn't show me anything. vi doesn't
> return to console properly.
Can you give a test case
>- I seem seem to get stuck in a "serial8250: too much work for irq%d"
> loop somewhat reliably. We have a rather demanding application with
> typically somewhere between 600 and 1000 byte packets being sent at
> 240Hz (roughly somewhere between 1.5 and 2 Mb/s). We run at baudrate
> 3500k. I get into this "too much work" thing already when running at
> 300 bytes per packet.
Do you get this message also at lower baud rates, say 115200?
What I am trying to understand is why you are spinning in the handler.
_With_ DMA you should hardly get into the serial handler under normal
conditions. Running at 3.5MB/sec should give one byte every 2.8us and
48 Bytes every ~137us. This looks like plenty of time to get out of
the handler. My *guess* is that serial8250_handle_irq() has IIR often
set to timeout and you end up fetching byte after byte.
This patch should protocol when and why you got into the handler.
diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
index 7111b22de000..59852069e4a0 100644
--- a/drivers/tty/serial/8250/8250_core.c
+++ b/drivers/tty/serial/8250/8250_core.c
@@ -1583,6 +1583,7 @@ int serial8250_handle_irq(struct uart_port *port, unsigned int iir)
status = serial_port_in(port, UART_LSR);
DEBUG_INTR("status = %x...", status);
+ trace_printk("l%d IIR %x LSR %x\n", port->line, iir, status);
if (status & (UART_LSR_DR | UART_LSR_BI)) {
if (up->dma)
@@ -1707,6 +1708,7 @@ static irqreturn_t serial8250_interrupt(int irq, void *dev_id)
spin_unlock(&i->lock);
+ trace_printk("%d e\n", irq);
DEBUG_INTR("end.\n");
return IRQ_RETVAL(handled);
>I hope this is of some use to you. I'll do more testing later.
Which SoC do you use and do you have DMA enabled?
>Thanks,
>Frans
Sebastian
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