On Thu, Sep 11, 2014 at 02:50:50PM +0200, Sebastian Andrzej Siewior wrote: > On 09/11/2014 02:32 PM, Peter Hurley wrote: > > On 09/11/2014 07:42 AM, Sebastian Andrzej Siewior wrote: > >> I also need a watchdog timer for TX since it seems that on omap3 the > >> DMA engine suddenly forgets to continue with DMA… > > > > One difference I noticed between the omap driver and the 8250 driver is > > the way modem status interrupts are handled. > > > > The omap driver only checks modem status for the UART_IIR_MSI interrupt type. > > The 8250 driver checks modem status at every interrupt (other than NO_INT). > > > > I think the UART_MSR_DCTS bit always reflects that the CTS input has changed > > between reads of the MSR _even if auto CTS is on_. So perhaps the hardware > > is being stopped by uart_handle_cts_change() when auto CTS is on? > > I doubt that. What I see from a timer debug is that the TX-FIFO level > is at 0, the DMA transfer for say 1024 bytes start. > The FIFO is filled to 64bytes and refilled so it doesn't drop below 50. > At the time of the stall I see that the DMA engine has outstanding > bytes which it should transfer and the TX FIFO is empty. If hardware > flow control stops the transfer, I would expect that the DMA engine > still fills the TX-FIFO until 64 and then waits. But it doesn't. > Writing bytes into the FIFO leads to bytes beeing sent (and I see them > on the other side) but the DMA transfer is still on hold. Canceling the > DMA transfer and re-programming the remaining bytes transfers the > remaining bytes. > > The odd thing is that I only triggered it with "less file". It doesn't > happen on regular console interaction or "cat large-file". And it only > triggers on beagle board xm (omap34xx) and I wasn't able to reproduce > it on am335x or dra7. The latter shares the same DMA engine as beagle > board xm. I can still reproduce it on am335x. I can get out of it as soon as something else gets written to the console though. # echo "<3>something" >/dev/kmsg Frans > > I remember also that I disabled the HW/SW float control just to make > sure it is not it. > > > > > Regards, > > Peter Hurley > > > > [The UPF_HARD_FLOW thing was pretty much just done for omap even though > > 8250 already had auto CTS/auto RTS. Serial core hardware flow control support > > needs a redo as drivers have pretty much tacked stuff on randomly.] > > Sebastian > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@xxxxxxxxxxxxxxxxxxx > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel -- 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
