On 21-05-18, 20:56, Frank Mori Hess wrote: > On Mon, May 21, 2018 at 5:16 AM, Vinod Koul <vinod.koul@xxxxxxxxxx> wrote: > >> > >> I understand the residue can't be read after terminate, that's why > >> reading the residue is step 2 in pause/residue/terminate. My question > >> was whether the entire sequence pause/residue/terminate taken as a > >> whole can or cannot lose data. Saying that individual steps can or > >> can't lose data is not enough, context is required. The key point is > >> whether pause flushes in-flight data to its destination or not. If it > >> does, and our residue is accurate, the terminate cannot cause data > >> loss. If pause doesn't flush, an additional step of flush_sync as > >> Lars suggested is required. So pause/flush_sync/residue/terminate > >> would be the safe sequence that cannot lose data. > > > > I wouldn't use cannot, shouldn't would be better here as it depends on HW and > > where all data has been buffered and if it can be flushed or not. > > > > Have you checked if pl330 supports such flushing? > > It does not, at least in the context of pausing. The dma-330 DMAEND > instruction flushes in-flight data to its destination, and there are > read/write barrier instructions also, but none of them can be injected > on the fly into a running dma thread. DMAKILL can be, but it discards > in-flight data. Currently, if an 8250 serial driver uses the pl330 > for rx dma, the result is possible data loss/corruption. If there was > a stronger pause capability, call it "cmd_sync_pause" which guaranteed > flushing of in-flight data to its destination and accurate residue > reading when paused, then the 8250 serial driver could check for > "cmd_sync_pause" and reject dma drivers that do not have that > capability. pl330.c would not advertise cmd_sync_pause. I don't know > if other dmaengine hardware would be able to support cmd_sync_pause or > not, I'm mostly just familiar with the pl330. The ep93xx_dma.c driver > for example has a m2p_hw_synchronize function which seems to do a > flush. Well looks like even adding support for sync_pause doesn't solve your issue on pl330. Do you want to move this to PIO mode then..? -- ~Vinod -- 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
 |