Le mardi 12 septembre 2023 à 08:47 +0000, Yong Wu (吴勇) a écrit : > On Mon, 2023-09-11 at 12:12 -0400, Nicolas Dufresne wrote: > > > > External email : Please do not click links or open attachments until > > you have verified the sender or the content. > > Hi, > > > > Le lundi 11 septembre 2023 à 10:30 +0800, Yong Wu a écrit : > > > From: John Stultz <jstultz@xxxxxxxxxx> > > > > > > This allows drivers who don't want to create their own > > > DMA-BUF exporter to be able to allocate DMA-BUFs directly > > > from existing DMA-BUF Heaps. > > > > > > There is some concern that the premise of DMA-BUF heaps is > > > that userland knows better about what type of heap memory > > > is needed for a pipeline, so it would likely be best for > > > drivers to import and fill DMA-BUFs allocated by userland > > > instead of allocating one themselves, but this is still > > > up for debate. > > > > > > Would be nice for the reviewers to provide the information about the > > user of > > this new in-kernel API. I noticed it because I was CCed, but > > strangely it didn't > > make it to the mailing list yet and its not clear in the cover what > > this is used > > with. > > > > I can explain in my words though, my read is that this is used to > > allocate both > > user visible and driver internal memory segments in MTK VCODEC > > driver. > > > > I'm somewhat concerned that DMABuf objects are used to abstract > > secure memory > > allocation from tee. For framebuffers that are going to be exported > > and shared > > its probably fair use, but it seems that internal shared memory and > > codec > > specific reference buffers also endup with a dmabuf fd (often called > > a secure fd > > in the v4l2 patchset) for data that is not being shared, and requires > > a 1:1 > > mapping to a tee handle anyway. Is that the design we'd like to > > follow ? > > Yes. basically this is right. > > > Can't > > we directly allocate from the tee, adding needed helper to make this > > as simple > > as allocating from a HEAP ? > > If this happens, the memory will always be inside TEE. Here we create a > new _CMA heap, it will cma_alloc/free dynamically. Reserve it before > SVP start, and release to kernel after SVP done. Ok, I see the benefit of having a common driver then. It would add to the complexity, but having a driver for the tee allocator and v4l2/heaps would be another option? > > Secondly. the v4l2/drm has the mature driver control flow, like > drm_gem_prime_import_dev that always use dma_buf ops. So we can use the > current flow as much as possible without having to re-plan a flow in > the TEE. >From what I've read from Yunfei series, this is only partially true for V4L2. The vb2 queue MMAP feature have dmabuf exportation as optional, but its not a problem to always back it up with a dmabuf object. But for internal SHM buffers used for firmware communication, I've never seen any driver use a DMABuf. Same applies for primary decode buffers when frame buffer compression or post- processing it used (or reconstruction buffer in encoders), these are not user visible and are usually not DMABuf. > > > > > Nicolas > > > > > > > > Signed-off-by: John Stultz <jstultz@xxxxxxxxxx> > > > Signed-off-by: T.J. Mercier <tjmercier@xxxxxxxxxx> > > > Signed-off-by: Yong Wu <yong.wu@xxxxxxxxxxxx> > > > [Yong: Fix the checkpatch alignment warning] > > > --- > > > drivers/dma-buf/dma-heap.c | 60 ++++++++++++++++++++++++++++---- > > ------ > > > include/linux/dma-heap.h | 25 ++++++++++++++++ > > > 2 files changed, 69 insertions(+), 16 deletions(-) > > > > [snip]
