On Wed, 2023-10-11 at 17:18 +0530, Vinod Koul wrote: > EXTERNAL EMAIL: Do not click links or open attachments unless you > know the content is safe > > On 10-10-23, 21:23, Kelvin.Cao@xxxxxxxxxxxxx wrote: > > On Mon, 2023-10-09 at 11:08 +0530, Vinod Koul wrote: > > > > > u64 size_to_transfer; > > > > > > Why cant the client driver write to doorbell, is there anything > > > which > > > prevents us from doing so? > > > > I think the potential challenge here for the client driver to ring > > db > > is that the client driver (host RC) is a different requester in the > > PCIe hierarchy compared to DMA EP, in which case PCIe ordering need > > to > > be considered. > > > > As PCIe ensures that reads don't pass writes, we can insert a read > > DMA > > operation with DMA_PREP_FENSE flag in between the two DMA writes > > (one > > for data transfer and one for notification) to ensure the ordering > > for > > the same requester DMA EP. I'm not sure if the RC could ensure the > > same > > ordering if the client driver issue MMIO write to db after the data > > DMA > > and read DMA completion, so that the consumer is guaranteed the > > transferred data is ready in memory when the db is triggered by the > > client MMIO write. I guess it's still doable with MMIO write but > > just > > some special consideration needed. > > Given that it is a single value, overhead of doing a new txn would be > higher than a mmio write! I think that should be preferred > > -- Ok. I'll remove the callback and come up with v7. Thank you Vinod for your comments. Kelvin
