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From: bigeasy@linutronix.de (Sebastian Andrzej Siewior)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH 09/16] tty: serial: 8250_dma: Add a TX trigger workaround for AM33xx
Date: Thu, 11 Sep 2014 14:50:50 +0200
Message-ID: <54119AAA.9080907@linutronix.de> (raw)
In-Reply-To: <5411967A.6090406@hurleysoftware.com>

On 09/11/2014 02:32 PM, Peter Hurley wrote:
> On 09/11/2014 07:42 AM, Sebastian Andrzej Siewior wrote:
>> I also need a watchdog timer for TX since it seems that on omap3 the
>> DMA engine suddenly forgets to continue with DMA?
> 
> One difference I noticed between the omap driver and the 8250 driver is
> the way modem status interrupts are handled.
> 
> The omap driver only checks modem status for the UART_IIR_MSI interrupt type.
> The 8250 driver checks modem status at every interrupt (other than NO_INT).
> 
> I think the UART_MSR_DCTS bit always reflects that the CTS input has changed
> between reads of the MSR _even if auto CTS is on_. So perhaps the hardware
> is being stopped by uart_handle_cts_change() when auto CTS is on?

I doubt that. What I see from a timer debug is that the TX-FIFO level
is at 0, the DMA transfer for say 1024 bytes start.
The FIFO is filled to 64bytes and refilled so it doesn't drop below 50.
At the time of the stall I see that the DMA engine has outstanding
bytes which it should transfer and the TX FIFO is empty. If hardware
flow control stops the transfer, I would expect that the DMA engine
still fills the TX-FIFO until 64 and then waits. But it doesn't.
Writing bytes into the FIFO leads to bytes beeing sent (and I see them
on the other side) but the DMA transfer is still on hold. Canceling the
DMA transfer and re-programming the remaining bytes transfers the
remaining bytes.

The odd thing is that I only triggered it with "less file". It doesn't
happen on regular console interaction or "cat large-file". And it only
triggers on beagle board xm (omap34xx) and I wasn't able to reproduce
it on am335x or dra7. The latter shares the same DMA engine as beagle
board xm.

I remember also that I disabled the HW/SW float control just to make
sure it is not it.

> 
> Regards,
> Peter Hurley
> 
> [The UPF_HARD_FLOW thing was pretty much just done for omap even though
> 8250 already had auto CTS/auto RTS. Serial core hardware flow control support
> needs a redo as drivers have pretty much tacked stuff on randomly.]

Sebastian

  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
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 [this message]
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

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