From: Peter Hurley <peter@hurleysoftware.com>
To: Tony Lindgren <tony@atomide.com>
Cc: Nicolas Schichan <nschichan@freebox.fr>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
gregkh@linuxfoundation.org, linux-serial@vger.kernel.org,
linux-kernel@vger.kernel.org, balbi@ti.com,
linux-omap@vger.kernel.org, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 03/16] tty: serial: 8250_core: read only RX if there is something in the FIFO
Date: Wed, 11 Feb 2015 15:42:06 -0500 [thread overview]
Message-ID: <54DBBE9E.90104@hurleysoftware.com> (raw)
In-Reply-To: <20150211200313.GE2531@atomide.com>
On 02/11/2015 03:03 PM, Tony Lindgren wrote:
> * Peter Hurley <peter@hurleysoftware.com> [150211 12:05]:
>> On 02/10/2015 12:46 PM, Peter Hurley wrote:
>>> On 02/10/2015 07:04 AM, Nicolas Schichan wrote:
>>>> 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())
>>>
>>> Thanks for this information; I see I was wrong about the cause of message.
>>>
>>> I think what happens during startup is that on this silicon clearing
>>> the rx fifo (by serial8250_clear_fifos()) clears data ready but not
>>> the rx timeout condition which causes a spurious rx interrupt when
>>> interrupts are enabled.
>>>
>>> So caught between two broken UARTs: one that underflows its rx fifo because
>>> of unsolicited rx reads and the other that generates spurious interrupt
>>> without unsolicited rx reads.
>>>
>>>
>>>> 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).
>>>
>>> Yes, IIR == UART_IIR_RX_TIMEOUT is to used indicate that data is in the rx fifo
>>> but has not reached the rx trigger level yet.
>>>
>>> ATM, I'm not exactly sure if there is a safe way to clear the spurious interrupt
>>> from the interrupt handler.
>>>
>>> I'm fairly certain the only way to clear the rx timeout interrupt is to read
>>> the rx fifo, but I think this would race with actual data arrival. IOW, there
>>> might not be a way to determine if the data read is spurious or not.
>>
>> Yep, I see no safe way to clear the spurious interrupt [1] and no idea how to
>> keep it from happening (other than via the unsolicited RX reads in
>> serial8250_do_startup).
>>
>> Unfortunately, I think this means we'll have to revert Sebastian's commit:
>>
>> commit 0aa525d11859c1a4d5b78fdc704148e2ae03ae13
>> Author: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
>> Date: Wed Sep 10 21:29:58 2014 +0200
>>
>> tty: serial: 8250_core: read only RX if there is something in the FIFO
>>
>> which just means OMAP3630 will be limited to using the omap_serial driver.
>
> Reverting makes sense to me if it has caused a regression. Maybe Sebastian
> can update his patch to do this based on some quirk flag instead?
That's fine with me. There's a 'bugs' field in struct 8250_uart_port and
UART_BUG_* defines in 8250/8250.h for that purpose.
Regards,
Peter Hurley
next prev parent reply other threads:[~2015-02-11 20:42 UTC|newest]
Thread overview: 98+ 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
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 [this message]
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
2014-09-12 9:40 ` Frans Klaver
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
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