Sorry to keep coming back to this, but I'm experiencing a bit of incredulity that you are saying what you seem to be saying. You seem to be saying dmaengine provides no way to permanently stop a transfer safely other than transferring the full number of bytes initially requested. So the proper resolution is the 8250 serial driver needs to remove rx dma support, because they are just trying to do something that is not supported. On Thu, May 17, 2018 at 12:19 AM, Vinod Koul <vinod.koul@xxxxxxxxxx> wrote: >> > Terminate is abort, data loss may happen here. >> >> Wait, are you saying if you do >> >> dma pause > > no data loss >> read residue > > here as well >> dma terminate > > Oh yes, we aborted... >> I see two ways of interpreting what you are saying. First, from the point of view of the user of the dmaengine api. From this point of view it is impossible for data loss to occur during pause or reading the residue, so saying they cause no data loss during pause/residue/terminate is meaningless. This is because the user can't confirm any data loss until after they have read the residue and the transfer is terminated, since optimistically the data may still be available if only the user would resume and allow the transfer to continue. Second there is the interpretation I want to believe. This is "no data loss on pause" means that after the pause, no data has been discarded by the dma controller hardware, in fact all the data it has read before being paused has been fully transferred to its destination. Reading the residue while paused gives you an accurate, up-to-date state of the paused transfer. Then finally, although in general dma terminate causes data loss, it does not in this case since we terminated while we were paused and read the up-to-date residue. This is the interpretation implicit in the 8250 serial driver. -- To unsubscribe from this list: send the line "unsubscribe linux-samsung-soc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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