On Wednesday 24 February 2016 08:50 AM, Peter Hurley wrote: > Just to follow-up on what Sebastian wrote. > > As he pointed out, these spurious interrupts are not timeout interrupts. > Since IIR_UART[0] == 1, no uart interrupt is pending. > > As he wrote, these count as spurious interrupts and trigger > interrupt shutdown at 100000 (unless acked as uart interrupts). Okay, by adding a printk to where the check for UART_IIR_NO_INT is in omap_8250_dma_handle_irq(), I do see that UART irq handler is called when there is apparently no interrupt. I don't see the error interrupt count in /proc/interrupts go up although the code is returning IRQ_NONE when this happens. I initially thought that must be because of the interrupt being IRQF_SHARED. But getting rid of IRQF_SHARED still does not lead to error count going up. I need to spend some more time to see what is going on. > These spurious interrupts very nearly correspond 1:1 (but not quite) > with each dma submission. So, for example, one test run had: > > @3Mbaud line rate > 195826 submits > 195823 completions > > 195704 spurious interrupts (ie., interrupts with IIR_UART[0] == 1) > 0 RLSI interrupts (no line errors) (IIR_UART == 0xc6) > 2 RX timeout interrupts (IIR_UART == 0xcc), > one during i/o test and one at the end of i/o test > 6 RDI interrupts (IIR_UART == 0xc4) > > The spurious interrupts occur with nearly 1:1 correspondence at _all_ > line rates. > > Presumbably, the 6 RDI interrupts are from too-slow submission of > the next DMA and the uart rx fifo has reached rx trigger level already. > [NOTE: we should at least be using ping-pong dma buffers for rx so that > there is always a next DMA buffer when the current buffer is completed]. > > There is no documentation in any of the OMAP TRMs regarding RDI > interrupts while in DMA mode. Some guidance from TI would be appreciated. UART interrupts triggering while UART_IIR_NO_INT is set is weird enough. I will check around internally with hardware folks here. Getting an answer might take time. But this is easily reproducible so I am optimistic we will get an answer soon. Regards, Sekhar -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
