On 04/12/2016 11:42 AM, Peter Hurley wrote: > On 04/12/2016 10:03 AM, Sebastian Andrzej Siewior wrote: >> On 04/11/2016 10:10 PM, Peter Hurley wrote: >>> On 04/11/2016 11:31 AM, Sebastian Andrzej Siewior wrote: >>>> On 04/11/2016 07:53 PM, Peter Hurley wrote: >>>>> On 04/11/2016 01:18 AM, John Ogness wrote: >>>>>> On 2016-04-05, Peter Hurley <peter@xxxxxxxxxxxxxxxxxx> wrote: >>>>>>> On 03/31/2016 01:41 AM, John Ogness wrote: >>>>>>>> It has been observed that the TX-DMA can stall >>>>>>> >>>>>>> Does this happen on any other OMAP part besides am335x? >>>>>>> I looked back over the LKML history of this and didn't see >>>>>>> any other design implicated in this problem. >>>>>> >>>>>> I just ran the tests again using 4.6-rc2. I am able to reproduce the >>>>>> dma-tx stall with am335x/edma and dra7/sdma. What "test" is reproducing this problem? >>>>> I thought we already established sdma was not to be used since >>>>> the hardware does not actually support pausing without data loss. >>>> >>>> This workaround was not invented for sdma but for edma (with am335x). >>> >>> According to John above, dra7/sdma requires this workaround. >> >> It was reported by Frans Klaver against am335x >> http://lkml.kernel.org/r/20140908183353.GB4686@ci00147.xsens-tech.local >> >> and I managed to reproduce this with his yocto image on dra7 and am335x: >> http://lkml.kernel.org/r/20140921204100.GA10111@xxxxxxxxxxxxx I overlooked Sebastian's statement from that message: This includes changing the baudrate (not by yocto but the driver sets it to 0 and then to the requested one) and this seems to be responsible for the "bad bytes". What is changing the baud rate to 0? How about get a stack trace for that? > [...] > >>> - hangs changing some unknown register if tx dma in progress >>> (ie., this termios change workaround) >> >> I think some registers are the baud-rate registers which pause engine. > > Let's back up here and focus on just this problem for now. > > Since this is observable on dra7/sdma, then it's not related to > the OMAP_DMA_TX_KICK problem. IOW, dropping tx dma support for am335x > does not make this go away, which is what I was asking. > > Now, if the DLL/DLH/MDR1 register writes are causing dma to stall, > then skipping those if they're unchanged should fix this, and then > pause/terminating in-progress DMA if any of these registers are being > written would be acceptable since some data loss is to be expected > when changing the baud rate without waiting. > -- 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
