Subject: [PATCH 05/15] tty: serial: Add 8250-core based omap driver

From: [email-masked] (Sebastian Andrzej Siewior)
Date: Fri, 15 Aug 2014 22:20:53 +0200

On 08/15/2014 09:33 PM, Lennart Sorensen wrote:
>> On the other hand if you use DMA then it can handle transfers > 64bytes
>> in one go and you can start transfers while the FIFO is not completely
>> empty.
> 
> You can dma more than the fifo size?

Yes. The UART asserts the DMA line as long as there is room for
$TRESHOLD number of bytes. So we never overflow the FIFO. That is why we
can't take any DMA channel but only *the* one.

>> There is patch in Greg's tty tree already where you are able to
>> configure the RX trigger level. We could wire this up once we agree
>> which levels we want support. The OMAP supports all levels from 1?63.
> 
> All? or just every 4 (that's what I just read in the DRA7xx docs).

All. Take a look at the RX_TRIGGER constant while comparing source vs
manual :)

Sebastian