linux-kernel - Re: [PATCH -mm v4 6/9] atmel_serial: Split the interrupt handler

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Date:	Thu, 14 Feb 2008 08:30:47 +0100
From:	michael <trimarchi@...dalf.sssup.it>
To:	Remy Bohmer <linux@...mer.net>
CC:	Haavard Skinnemoen <hskinnemoen@...el.com>, fabio@...dalf.sssup.it,
	Andrew Victor <linux@...im.org.za>,
	Chip Coldwell <coldwell@...hat.com>,
	Marc Pignat <marc.pignat@...s.ch>,
	David Brownell <david-b@...bell.net>,
	linux-kernel@...r.kernel.org, Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [PATCH -mm v4 6/9] atmel_serial: Split the interrupt handler

Hi,
Remy Bohmer wrote:
> Hello All,
>
>   
>> All works now for me with preempt-rt. The problem is using hrtimer.
>> I think that hrtimer are executed with interrupts disabled so, if
>> this happen when I must receive a char, i have an overrun.
>>     
>
> No, they share the same interrupt line...
>   
I think that the hrtimer use and other interrupt line. The 
AT91SAM9260_ID_TC2.
> So, while the timer interrupt handler is running, the serial handler
> has to wait until the timer interrupt handler has finished.
> Notice that the HRT interrupt handler is quite heavy and takes a long
> time to complete.
>   
The problem is the heavy of HRT interrupt handler of course.
> And, as I already mentioned, related to the 1 byte FIFO and a
> interrupt latency of about 85us (without HRT), it is logical that you
> can get an overrun at the higher serial speeds... (>=115200bps)
>
>   
I don't have the same problem without the hrtimer, I suppose the the 
timer latency
is not so heavy.
>> The only solution was the dma support to serial device.
>>     
>
> Or, use flow control?
>
>
>   
Yes :)

Michael

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