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From: frans.klaver@xsens.com (Frans Klaver)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH v8 00/18] 8250-core based serial driver for OMAP + DMA
Date: Mon, 8 Sep 2014 20:33:53 +0200
Message-ID: <20140908183353.GB4686@ci00147.xsens-tech.local> (raw)
In-Reply-To: <20140908151501.GA22584@linutronix.de>

On Mon, Sep 08, 2014 at 05:15:01PM +0200, Sebastian Andrzej Siewior wrote:
> * Frans Klaver | 2014-09-08 16:46:18 [+0200]:
> 
> >- 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?

I don't get this message at lower data rates. Haven't tested lower baud
rates yet.

> 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);
> 

Thanks. I'll give it a spin on Wednesday.


> >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?

am335x, DMA is enabled, unless I need to do something extra in the
device tree. We depend on am335x.dtsi, so I would think that would be
automatic if CONFIG_SERIAL_8250_DMA=y.

Thanks,
Frans

  parent reply index

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-09-05 19:02 Sebastian Andrzej Siewior
2014-09-05 19:02 ` [PATCH 01/18] tty: serial: 8250_core: provide a function to export uart_8250_port Sebastian Andrzej Siewior
2014-09-05 19:02 ` [PATCH 02/18] tty: serial: 8250_core: allow to overwrite & export serial8250_startup() Sebastian Andrzej Siewior
2014-09-05 19:02 ` [PATCH 03/18] tty: serial: 8250_core: allow to set ->throttle / ->unthrottle callbacks Sebastian Andrzej Siewior
2014-09-08 23:33   ` Greg Kroah-Hartman
2014-09-09  0:41     ` Tony Lindgren
2014-09-05 19:02 ` [PATCH 04/18] tty: serial: 8250_core: add run time pm Sebastian Andrzej Siewior
2014-09-05 19:02 ` [PATCH 05/18] tty: serial: 8250_core: read only RX if there is something in the FIFO Sebastian Andrzej Siewior
2014-09-05 19:02 ` [PATCH 06/18] tty: serial: 8250_core: user the ->line argument as a hint in serial8250_find_match_or_unused() Sebastian Andrzej Siewior
2014-09-05 19:02 ` [PATCH 07/18] tty: serial: 8250_core: remove UART_IER_RDI in serial8250_stop_rx() Sebastian Andrzej Siewior
2014-09-05 19:02 ` [PATCH 08/18] tty: serial: Add 8250-core based omap driver Sebastian Andrzej Siewior
2014-09-08 16:39   ` Tony Lindgren
2014-09-05 19:02 ` [PATCH 09/18] tty: serial: 8250_dma: handle error on TX submit Sebastian Andrzej Siewior
2014-09-05 19:02 ` [PATCH 10/18] tty: serial: 8250_dma: enqueue RX dma again on completion Sebastian Andrzej Siewior
2014-09-05 19:02 ` [PATCH 11/18] tty: serial: 8250_dma: Add a TX trigger workaround for AM33xx Sebastian Andrzej Siewior
2014-09-08 16:41   ` Tony Lindgren
2014-09-08 16:45     ` Sebastian Andrzej Siewior
2014-09-05 19:02 ` [PATCH 12/18] tty: serial: 8250_dma: optimize the xmit path due to UART_BUG_DMA_TX Sebastian Andrzej Siewior
2014-09-05 19:02 ` [PATCH 13/18] tty: serial: 8250_dma: keep own book keeping about RX transfers Sebastian Andrzej Siewior
2014-09-05 19:02 ` [PATCH 14/18] tty: serial: 8250_dma: handle the when UART response while DMA remains idle Sebastian Andrzej Siewior
2014-09-05 19:02 ` [PATCH 15/18] tty: serial: 8250_dma: add pm runtime Sebastian Andrzej Siewior
2014-09-05 19:02 ` [PATCH 16/18] arm: dts: am33xx: add DMA properties for UART Sebastian Andrzej Siewior
2014-09-05 19:02 ` [PATCH 17/18] arm: dts: dra7: " Sebastian Andrzej Siewior
2014-09-05 19:02 ` [PATCH 18/18] tty: serial: 8250: omap: add dma support Sebastian Andrzej Siewior
2014-09-08 14:46 ` [PATCH v8 00/18] 8250-core based serial driver for OMAP + DMA Frans Klaver
2014-09-08 15:15   ` Sebastian Andrzej Siewior
2014-09-08 16:33     ` Sebastian Andrzej Siewior
2014-09-08 18:25       ` Frans Klaver
2014-09-08 18:33     ` Frans Klaver [this message]
2014-09-09 19:41       ` Sebastian Andrzej Siewior
2014-09-10 14:15         ` Frans Klaver
2014-09-10 16:56           ` Sebastian Andrzej Siewior
2014-09-08 17:40 ` Tony Lindgren
2014-09-08 17:55   ` Tony Lindgren
2014-09-09  7:33     ` Sebastian Andrzej Siewior

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