On Wed, Nov 20, 2019 at 1:02 PM Christian König <christian.koenig@xxxxxxx> wrote: > > > What am I missing? > The assumption is that when you want to create a vmap of a DMA-buf > buffer the buffer needs to be pinned somehow. > > E.g. without dynamic dma-buf handling you would need to have an active > attachment. With dynamic handling the requirements could be lowered to > using the pin()/unpin() callbacks. Yeah right now everyone seems to have an attachment, and that's how we get away with all this. But the interface isn't supposed to work like that, dma_buf_vmap/unmap is supposed to be a stand-alone thing (you can call it directly on the struct dma_buf, no need for an attachment). Also I don't think non-dynamic drivers should ever call pin/unpin, not their job, holding onto a mapping should be enough to get things pinned. > You also can't lock/unlock inside your vmap callback because you don't > have any guarantee that the pointer stays valid as soon as your drop > your lock. Well that's why I asked where the pin/unpin pair is. If you lock&pin, then you do know that the pointer will stay around. But looks like the original patch from Dave for ttm based drivers played fast&loose here with what should be done. > BTW: What is vmap() still used for? udl, bunch of other things (e.g. bunch of tiny drivers). Not much, but not stuff we can drop. -Daniel > > Regards, > Christian. > > Am 20.11.19 um 12:47 schrieb Daniel Vetter: > > Hi all, > > > > I've been looking at dma_buf_v(un)map, with a goal to standardize > > locking for at least dynamic dma-buf exporters/importers, most likely > > by requiring dma_resv_lock. And I got questions around how this is > > supposed to work, since a big chunk of drivers seem to entirely lack > > locking around ttm_bo_kmap. Two big ones: > > > > - ttm_bo_kmap looks at bo->mem to figure out what/where to kmap to get > > at that buffer. bo->mem is supposed to be protected with > > dma_resv_lock, but at least amgpu/nouveau/radeon/qxl don't grab that > > in their prime vmap function. > > > > - between the vmap and vunmap something needs to make sure the backing > > storage doesn't move around. I didn't find that either anywhere, > > ttm_bo_kmap simply seems to set up the mapping, leaving locking and > > refcounting to callers. > > > > - vram helpers have at least locking, but I'm still missing the > > refcounting. vmwgfx doesn't bother with vmap. > > > > What am I missing? > > > > Thanks, Daniel > -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
