On Wed, 2023-10-11 at 16:36 +0000, Kelvin.Cao@xxxxxxxxxxxxx wrote: > EXTERNAL EMAIL: Do not click links or open attachments unless you > know the content is safe > > 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. > Hi Vinod, I've submitted v7 (title: [PATCH v7 0/1] Switchtec Switch DMA Engine Driver) which removed the callback support for wimm as you suggested. Please let me know if that looks good to you. Thanks, Kelvin
