Linux-ARM-Kernel Archive on lore.kernel.org
 help / color / Atom feed
From: nschichan@freebox.fr (Nicolas Schichan)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH 03/16] tty: serial: 8250_core: read only RX if there is something in the FIFO
Date: Tue, 10 Feb 2015 13:04:23 +0100
Message-ID: <54D9F3C7.5000809@freebox.fr> (raw)
In-Reply-To: <54D9441B.7070403@hurleysoftware.com>

On 02/10/2015 12:34 AM, Peter Hurley wrote:
> Hi Nicolas,
> 
> Thanks for the report.
> 
[...]
>> When a caracter is received on the UART while the kernel is printing
>> the boot messages, as soon as the kernel configures the UART for
>> receiving (after root filesystem mount), it gets stuck printing the
>> following message repeatedly:
>>
>> serial8250: too much work for irq29
>>
>> Once stuck, the reception of another character allows the boot process
>> to finish.
>>
>> From what I can gather, when we hit that, the UART_IIR_NO_INT is 0 (so the
>> interrupt is raised), but the UART_LSR_DR bit is 0 as well so the UART_RX
>> register is never read to clear the interrupt.
> 
> The "too much work" message means serial8250_handle_irq() is returning 0,
> ie., not handled. Which in turn means IIR indicates no interrupt is pending
> (UART_IIR_NO_INT == 1).
> 
> Can you log the register values for LSR and IIR at both patch locations
> in serial8250_do_startup()?
> 
> (I can get you a debug patch, if necessary. Let me know)

Hi Peter,

Thanks for your reply.

Here is what I have when the issue is triggered:

[   12.154877] lsr 0x60 / iir 0x01
[   12.158071] lsr 0x60 / iir 0x01
[   12.161438] serial8250: too much work for irq29
[   12.165982] lsr 0x60 / iir 0x0c
[   12.169354] serial8250: too much work for irq29
[   12.173900] lsr 0x60 / iir 0x0c
(previous two messages are repeated and printk_ratelimited())

When the issue is not triggered:

[   10.784871] lsr 0x60 / iir 0x01
[   10.788066] lsr 0x60 / iir 0x01
[   10.794734] VFS: Mounted root (nfs filesystem) readonly on device 0:13.
[   10.801654] devtmpfs: mounted
[   10.805169] Freeing unused kernel memory: 184K (807be000 - 807ec000)
(userland takes over after that)

I have also displayed the IIR and LSR registers when the "too much fork for
IRQ" condition is triggered.

In the serial8250_do_startup(), before the interrupt are unmasked at the end,
the IIR looks sane and UART_IIR_NO_INT bit is set. When stuck
serial8250_interrupt(), UART_IIR_NO_INT is cleared and the interrupt ID is set
to 0xc which is not handled by the kernel at this time (the Kirkwood datasheet
 indicates that it is some kind of timeout condition from what I can gather).

Here is the corresponding debug patch, for reference (against a 3.19 kernel
this time):

diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_
index 11c6685..ed93741 100644
--- a/drivers/tty/serial/8250/8250_core.c
+++ b/drivers/tty/serial/8250/8250_core.c
@@ -1661,6 +1661,12 @@ static int exar_handle_irq(struct uart_port *port)
        return ret;
 }

+static inline void show_lsr_iir(struct uart_port *port)
+{
+       printk("lsr 0x%02x / iir 0x%02x\n", serial_port_in(port, UART_LSR),
+              serial_port_in(port, UART_IIR));
+}
+
 /*
  * This is the serial driver's interrupt routine.
  *
@@ -1705,6 +1711,8 @@ static irqreturn_t serial8250_interrupt(int irq, void *dev
                        /* If we hit this, we're dead. */
                        printk_ratelimited(KERN_ERR
                                "serial8250: too much work for irq%d\n", irq);
+                       if (printk_ratelimit())
+                               show_lsr_iir(port);
                        break;
                }
        } while (l != end);
@@ -2107,6 +2115,7 @@ int serial8250_do_startup(struct uart_port *port)
        /*
         * Clear the interrupt registers.
         */
+       show_lsr_iir(port);
        if (serial_port_in(port, UART_LSR) & UART_LSR_DR)
                serial_port_in(port, UART_RX);
        serial_port_in(port, UART_IIR);
@@ -2269,6 +2278,7 @@ dont_test_tx_en:
         * saved flags to avoid getting false values from polling
         * routines or the previous session.
         */
+       show_lsr_iir(port);
        if (serial_port_in(port, UART_LSR) & UART_LSR_DR)
                serial_port_in(port, UART_RX);
        serial_port_in(port, UART_IIR);

Regards,

-- 
Nicolas Schichan
Freebox SAS

  parent reply index

Thread overview: 97+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-09-10 19:29 [PATCH 00/16 v9] omap 8250 based uart + DMA Sebastian Andrzej Siewior
2014-09-10 19:29 ` [PATCH 01/16] tty: serial: 8250_core: allow to set ->throttle / ->unthrottle callbacks Sebastian Andrzej Siewior
2014-09-10 19:29 ` [PATCH 02/16] tty: serial: 8250_core: add run time pm Sebastian Andrzej Siewior
2014-09-29  9:46   ` Frans Klaver
2014-09-29 13:39     ` Sebastian Andrzej Siewior
2014-09-10 19:29 ` [PATCH 03/16] tty: serial: 8250_core: read only RX if there is something in the FIFO Sebastian Andrzej Siewior
2015-02-09 13:34   ` Nicolas Schichan
2015-02-09 23:34     ` Peter Hurley
2015-02-10  9:32       ` Sebastian Andrzej Siewior
2015-02-10 12:04       ` Nicolas Schichan [this message]
2015-02-10 17:46         ` Peter Hurley
2015-02-11 20:01           ` Peter Hurley
2015-02-11 20:03             ` Tony Lindgren
2015-02-11 20:42               ` Peter Hurley
2015-02-12  8:45                 ` Sebastian Andrzej Siewior
2015-02-12  9:40                   ` Russell King - ARM Linux
2015-02-12 16:32                   ` Peter Hurley
2015-02-12 19:23                     ` Sebastian Andrzej Siewior
2015-02-12 19:55                       ` Peter Hurley
2015-02-12 20:34                         ` Sebastian Andrzej Siewior
2015-02-13 18:51                         ` Sebastian Andrzej Siewior
2015-02-13 23:15                           ` Russell King - ARM Linux
2015-02-15 17:32                             ` [PATCH] serial: 8250: Revert "tty: serial: 8250_core: read only RX if there is something in the FIFO" Sebastian Andrzej Siewior
2015-05-12 20:25                               ` Tony Lindgren
2014-09-10 19:29 ` [PATCH 04/16] tty: serial: 8250_core: use the ->line argument as a hint in serial8250_find_match_or_unused() Sebastian Andrzej Siewior
2014-09-10 19:30 ` [PATCH 05/16] tty: serial: 8250_core: remove UART_IER_RDI in serial8250_stop_rx() Sebastian Andrzej Siewior
2014-09-11 11:19   ` Heikki Krogerus
2014-09-10 19:30 ` [PATCH 06/16] tty: serial: Add 8250-core based omap driver Sebastian Andrzej Siewior
2014-09-11 11:57   ` Peter Hurley
2014-09-16 17:01     ` Sebastian Andrzej Siewior
2014-09-29  9:38   ` Frans Klaver
2014-09-29 13:27     ` Sebastian Andrzej Siewior
2014-09-29 13:34       ` Frans Klaver
2014-09-10 19:30 ` [PATCH 07/16] tty: serial: 8250_dma: handle error on TX submit Sebastian Andrzej Siewior
2014-09-10 19:30 ` [PATCH 08/16] tty: serial: 8250_dma: enqueue RX dma again on completion Sebastian Andrzej Siewior
2014-09-10 19:30 ` [PATCH 09/16] tty: serial: 8250_dma: Add a TX trigger workaround for AM33xx Sebastian Andrzej Siewior
2014-09-11 11:17   ` Heikki Krogerus
2014-09-11 11:42     ` Sebastian Andrzej Siewior
2014-09-11 12:32       ` Peter Hurley
2014-09-11 12:50         ` Sebastian Andrzej Siewior
2014-09-11 14:35           ` Peter Hurley
2014-09-15 17:01             ` Sebastian Andrzej Siewior
2014-09-16 16:55               ` Sebastian Andrzej Siewior
2014-09-17 12:20                 ` Peter Hurley
2014-09-17 16:25                   ` Sebastian Andrzej Siewior
2014-09-29 16:15                   ` Sebastian Andrzej Siewior
2014-09-11 15:11           ` Frans Klaver
2014-09-11 16:04             ` Sebastian Andrzej Siewior
2014-09-11 17:04               ` Frans Klaver
2014-09-12  7:23                 ` Sebastian Andrzej Siewior
     [not found]                   ` <20140912094010.GE28458@ci00147.xsens-tech.local>
2014-09-12  9:51                     ` Sebastian Andrzej Siewior
2014-09-12 10:28                       ` Frans Klaver
2014-09-15 16:42                         ` Sebastian Andrzej Siewior
2014-09-16  9:05                           ` Frans Klaver
2014-09-16 12:42                             ` Frans Klaver
2014-09-16 14:23                               ` Frans Klaver
2014-09-17 10:28                           ` Frans Klaver
2014-09-21 20:41                             ` Sebastian Andrzej Siewior
2014-09-22  9:28                               ` Frans Klaver
2014-09-24  7:56                                 ` Sebastian Andrzej Siewior
2014-09-25 15:14                                 ` Sebastian Andrzej Siewior
2014-09-25 15:18                                   ` Frans Klaver
2014-09-29  8:50                                   ` Frans Klaver
2014-09-29  9:54                                     ` Sebastian Andrzej Siewior
2014-09-29 10:30                                       ` Frans Klaver
2014-09-30  8:44                                         ` Frans Klaver
2014-10-02 10:27                                           ` Sebastian Andrzej Siewior
2014-10-13 14:55                                             ` Frans Klaver
2014-09-23 17:03                               ` Peter Hurley
2014-09-24  7:53                                 ` Sebastian Andrzej Siewior
2014-09-25 10:42                                   ` Sebastian Andrzej Siewior
2014-09-25 11:31                                     ` Peter Hurley
2014-09-25 13:11                                       ` Sebastian Andrzej Siewior
2014-09-17 16:34       ` Sebastian Andrzej Siewior
2014-09-19 10:22         ` Heikki Krogerus
2014-09-19 10:58           ` Sebastian Andrzej Siewior
2014-09-19 11:25             ` Peter Hurley
2014-09-22  7:46             ` Heikki Krogerus
2014-09-25  9:24               ` Sebastian Andrzej Siewior
2014-09-10 19:30 ` [PATCH 10/16] tty: serial: 8250_dma: optimize the xmit path due to UART_BUG_DMA_TX Sebastian Andrzej Siewior
2014-09-10 19:30 ` [PATCH 11/16] tty: serial: 8250_dma: keep own book keeping about RX transfers Sebastian Andrzej Siewior
2014-09-10 19:30 ` [PATCH 12/16] tty: serial: 8250_dma: handle the UART RDI event while DMA remains idle Sebastian Andrzej Siewior
2014-09-29  9:23   ` Frans Klaver
2014-09-10 19:30 ` [PATCH 13/16] tty: serial: 8250_dma: add pm runtime Sebastian Andrzej Siewior
2014-09-29  9:26   ` Frans Klaver
2014-09-29  9:56     ` Sebastian Andrzej Siewior
2014-09-10 19:30 ` [PATCH 14/16] arm: dts: am33xx: add DMA properties for UART Sebastian Andrzej Siewior
2014-09-10 19:30 ` [PATCH 15/16] arm: dts: dra7: " Sebastian Andrzej Siewior
2014-09-10 19:30 ` [PATCH 16/16] tty: serial: 8250: omap: add dma support Sebastian Andrzej Siewior
2014-09-12 22:43 ` [PATCH 00/16 v9] omap 8250 based uart + DMA Tony Lindgren
2014-09-15 11:50   ` Sebastian Andrzej Siewior
2014-09-16 12:57     ` Sebastian Andrzej Siewior
2014-09-16 16:48       ` Tony Lindgren
2014-09-16 21:30         ` Tony Lindgren
2014-09-17  8:38           ` Sebastian Andrzej Siewior
2014-09-17  9:05 ` Sebastian Andrzej Siewior
2014-09-26 16:02   ` Greg KH

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=54D9F3C7.5000809@freebox.fr \
    --to=nschichan@freebox.fr \
    --cc=linux-arm-kernel@lists.infradead.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-ARM-Kernel Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-arm-kernel/0 linux-arm-kernel/git/0.git
	git clone --mirror https://lore.kernel.org/linux-arm-kernel/1 linux-arm-kernel/git/1.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-arm-kernel linux-arm-kernel/ https://lore.kernel.org/linux-arm-kernel \
		linux-arm-kernel@lists.infradead.org
	public-inbox-index linux-arm-kernel

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.infradead.lists.linux-arm-kernel


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git