[PATCH v7] 8250-core based serial driver for OMAP + DMA

Peter Hurley peter at hurleysoftware.com
Mon Aug 18 08:15:17 PDT 2014

On 08/15/2014 04:28 PM, Tony Lindgren wrote:
> * Sebastian Andrzej Siewior <bigeasy at linutronix.de> [140815 12:16]:
>> On 08/15/2014 08:17 PM, Lennart Sorensen wrote:
>>> Are you saying that with the new driver you have to respond to the RX
>>> irq faster than before to avoid overflows?  It is not quite clear.
>> Yes. The irq fires 46 bytes giving you 16 bytes buffer before overflow
>> vs 63 bytes buffer the old one had.
>>> I do think 40000 interrupts to handle 40000 bytes of date does seem a
>>> tad inefficient, so dropping to 854 looks a lot nicer.  Was the omap
>>> driver not using the fifo trigger levels at all?
>> It configured the trigger levels to 1 for RX and 16 for TX.
> Hmm that weird RX trigger level is a workaround for lost characters.
> See commit 0ba5f66836 (tty: serial: OMAP: use a 1-byte RX FIFO
> threshold in PIO mode :)

That commit looks like it should have been specific to the silicon
exhibiting the rx timeout bug.

Peter Hurley

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