On 06/09/2014 01:23 PM, Daniel Stone wrote: > Hi, > > On 9 June 2014 12:06, Pekka Paalanen <[email protected] > <mailto:[email protected]>> wrote: > > On Mon, 9 Jun 2014 11:00:04 +0200 > Benjamin Gaignard <[email protected] > <mailto:[email protected]>> wrote: > > One of the main comment on the latest patches was that wl_dmabuf use > > DRM for buffer allocation. > > This appear to be an issue since wayland doesn't want to rely on one > > specific framework (DRM, or V4L2) for buffer allocation, so we have > > start working on a "central dmabuf allocation" on kernel side. The > > goal is provide some as generic as possible to make it acceptable by > > wayland. > > Why would Wayland need a central allocator for dmabuf? > > > I think you've just answered your own question further below: > > > > On my hardware the patches you have (+ this one on gstwaylandsink > > https://bugzilla.gnome.org/show_bug.cgi?id=711155 > > <https://urldefense.proofpoint.com/v1/url?u=https://bugzilla.gnome.org/show_bug.cgi?id%3D711155&k=oIvRg1%2BdGAgOoM1BIlLLqw%3D%3D%0A&r=l5Ago9ekmVFZ3c4M6eauqrJWGwjf6fTb%2BP3CxbBFkVM%3D%0A&m=NHSSDNdXVt2oCxexwhcqQAQSZ3K6Xa8Zvuv0jMYfS2c%3D%0A&s=f6d8c24d7fa4ccdacae79aeaa8221773d892350a191f96cb3bab4f542fb3ad1c>) > allow me to do zero > > copy between the hardware video decoder and the display engine. I > > don't have implemented GPU yet because my hardware is able to do > > compose few video overlays planes and it was enough for my tests. > > Right. > > What I have been thinking is, that the compositor must be able to use > the new wl_buffer and we need to guarantee that before-hand. If the > compositor fails to use a wl_buffer when the client has already > attached it to a wl_surface and it is time to repaint, it is too late > and the user will see a glitch. Recovering from that requires asking > the client to provide a new wl_buffer of a different kind, which might > take time. Or a very rude compositor would just send a protocol error, > and then we'd get bug reports like "the video player just disappears > when I try to play (and ps. I have an old kernel that doesn't support > importing whatever)". > > I believe we must allow the compositor to test the wl_buffer before it > is usable for the client. That is the reason for the roundtrippy > design > of the below proposal. > > > A central allocator would solve these issues, by having everyone agree > on the restrictions upfront, instead of working out which of the media > decode engine, camera, GPU, or display controller is the lowest common > denominator, and forcing all allocations through there. > > One such solution was discussed a while back WRT ION: > https://lwn.net/Articles/565469/ > <https://urldefense.proofpoint.com/v1/url?u=https://lwn.net/Articles/565469/&k=oIvRg1%2BdGAgOoM1BIlLLqw%3D%3D%0A&r=l5Ago9ekmVFZ3c4M6eauqrJWGwjf6fTb%2BP3CxbBFkVM%3D%0A&m=NHSSDNdXVt2oCxexwhcqQAQSZ3K6Xa8Zvuv0jMYfS2c%3D%0A&s=36b71b58f7fc6f3d594529cc674364a23718e5cbb38a439e4a9c628848a13b3a> > > See the 'possible solutions' part for a way for people to agree on > restrictions wrt tiling, stride, contiguousness, etc.
Hi! I think before deciding on something like this, one needs also to account for the virtual drivers like vmwgfx. Here, a dma-buf internally holds an opaque handle to an object on the host / hypervisor, and the actual memory buffer is only temporarily allocated for dma-buf operations that strictly need it. Not to hold the data while transferring it between devices or applications. Let's say you'd want to use a USB display controller in a virtual machine with the vmwgfx exported prime objects, for example. There's no common denominator. The vmwgfx driver would need to read the dma-buf data from the host object at sg-table export (dma-buf map) time. Whereas if you just want to share data between a wayland server and client, no pages are ever allocated and the only thing passed around is in effect the opaque handle to the host / hypervisor object. I'm currently having trouble seeing how a central allocator would be able to deal with this? /Thomas > > Cheers, > Daniel > > > _______________________________________________ > wayland-devel mailing list > [email protected] > https://urldefense.proofpoint.com/v1/url?u=http://lists.freedesktop.org/mailman/listinfo/wayland-devel&k=oIvRg1%2BdGAgOoM1BIlLLqw%3D%3D%0A&r=l5Ago9ekmVFZ3c4M6eauqrJWGwjf6fTb%2BP3CxbBFkVM%3D%0A&m=NHSSDNdXVt2oCxexwhcqQAQSZ3K6Xa8Zvuv0jMYfS2c%3D%0A&s=c4f94901274570868164b5aac297336d544bdba1bc12bda6c09b915fa5495423 _______________________________________________ wayland-devel mailing list [email protected] http://lists.freedesktop.org/mailman/listinfo/wayland-devel
