On 07-01-20, 13:18, Dave Jiang wrote: > Dropped everyone except dmaengine and related parties. > > On 1/7/20 11:17 AM, Dave Jiang wrote: > > > > > > On 1/7/20 10:45 AM, Dave Jiang wrote: > > > > > > > > > On 12/26/19 10:58 PM, Vinod Koul wrote: > > > > On 17-12-19, 16:34, Dave Jiang wrote: > > > > > Create a char device region that will allow acquisition of > > > > > user portals in > > > > > order to allow applications to submit DMA operations. A char > > > > > device will be > > > > > created per work queue that gets exposed. The workqueue type "user" > > > > > is used to mark a work queue for user char device. For example if the > > > > > workqueue 0 of DSA device 0 is marked for char device, then > > > > > a device node > > > > > of /dev/dsa/wq0.0 will be created. > > > > > > > > do we really want to create a device specific interface..? why not move > > > > it to dmaengine core and create a dmaengine device for userland to > > > > submit dma operations? > > > > > > I'm keeping an eye on the uacce framework [1] progress. If that goes > > > upstream then there's probably not any reason for dmaengine to export > > > that. Otherwise then yes that would be reasonable. Are you thinking that > > > the uacce guys should consider doing that for dmaengine instead? > > > > > > The char device export in idxd driver is a bridge solution until we > > > bottom out on whichever interface to provide the generic framework. > > > > Oops forgot to provide URL > > > > [1]: https://lkml.org/lkml/2019/12/15/332 > > So after thinking a bit more and talking to Dan, I think there's some > confusion that needs explanation on how the idxd user portal works vs > traditional DMA engines. For idxd, the char device allows the user app to > mmap() a 4k region called a portal. With that portal address the user can > use either MOVDIR64B or ENQCMD CPU instruction to directly submit a DMA > descriptor to the device without touching the kernel. I think this part is > device specific and probably can only be provided by the driver for now. > > I think you on the other hand are looking for a kernel assisted DMA > operation submission from userspace through the dmaengine framework correct? > We would expose a char device for a channel that allows a user app to submit > DMA operations via ioctls? That is something the idxd driver needs as well > when the operation hits a point where the user portal is saturated and we > need kernel assistance to move forward. But I would like to mark this as > follow on work for me to add to dmaengine as a common framework. Yeah agreed that is something we would need eventually... -- ~Vinod
