Re: [PATCH 0/4] serial: omap: robustify for high speed transfers

[Sebastian Andrzej Siewior]

On 02/23/2016 10:59 AM, Sekhar Nori wrote:
>> With the am335x (Beaglebone Black, eDMA engine) I see 1000 DMA
>> interrupts and 1000 spurious UART interrupts. The spurious UART
>> interrupts arrive 30-50us _before_ the DMA interrupts. Always.
>>
>> If I disable UART timeout interrupts (RDI), the same test generates no
>> spurious UART interrupts. Only 1000 DMA interrupts.
> 
> To be clear, these interrupts are not caught as spurious by the
> interrupt controller (INTC). They are detected by INTC as UART
> interrupts. Just that you don't expect a timeout interrupt to happen at
> the time you see the interrupt, correct?

>From what I remember the INTC says it is UART, correct.
But UART's status register says "no interrupt" (IIR has UART_IIR_NO_INT
set). So the UART driver returns IRQ_NONE which counts as spurious.

It is just that once you disable RDI there are no more interrupts coming
during DMA transfer.

> Thanks,
> Sekhar
> 
Sebastian