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List:       linux-serial
Subject:    Re: mxs auart timeout waiting for transmission with hw flow control
From:       Hector Palacios <hector.palacios () digi ! com>
Date:       2013-09-30 16:41:25
Message-ID: 5249A9B5.2080903 () digi ! com
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Hi Uwe,

On 09/30/2013 06:20 PM, Uwe Kleine-König wrote:
> Hi Hector,
>
> On Mon, Sep 30, 2013 at 06:07:19PM +0200, Hector Palacios wrote:
>> I saw your patch at
>> http://www.spinics.net/lists/stable/msg12952.html and I believe I'm
>> having a similar issue when not using the port as console.
>>
>> With hardware flow control enabled transmission fails at low
>> baudrates (9600,38400). Apparently the transmitter closes the port
> Which kernel are you using? I think there were some other fixes
> concering flow control some time ago.

v3.10. The driver is pretty close to current status.

>> before the data has been really shifted out (or even transferred by
>> the DMA). While the console functions check the status of
>> AUART_STAT_BUSY, the standard functions don't, and the AUART is busy
>> when shutdown is called at low baudrates.
>>
>> I also see the function uart_wait_until_sent() of serial_core.c
>> getting out with timeout expired. At 9600 baud, this function waits
>> 2 or 4 jiffies. Increasing (a lot) the timeout of this function
>> solves the problem. I monitored the time it takes for TX to be empty
>> and it resulted in sometimes around 200 jiffies (@9600).
> Again with flow control and another imx28 on the opposite side? Does it
> work without flow control? Is CTS busy for some time? In that case a
> simple timeout isn't appropriate. Using console and flow control on the
> same port might be hairy, not sure though.

Yes, two imx28 devices with hw flow control enabled. Without flow control it works.
CTS is not busy. At these low baudrates the CPU is fast enough to process the received 
data in time.
I'm not using the AUART as console but as a standard port.

>> The issue can be reproduced using two iMX28 devices (transmitting
>> between two ports on the same platform usually works fine),
>> configuring a low baudrate (9600) and hardware flow enabled, and
>> sending a file of 40K, for example. The last ~200 bytes or so are
>> typically not sent over the line.
> I currently don't have the time and machines to test, but maybe the
> freescale guys (added Fabio to Cc, too) might want to test it.
>
> Best regards from Freiburg

I wish I could drop by Freiburg one of these days! Love the city (and the beer).

Best regards,
--
Hector Palacios
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