2015-02-03 13:28 GMT+01:00 Russell King - ARM Linux <linux at arm.linux.org.uk>: > On Tue, Feb 03, 2015 at 08:48:56AM +0100, Daniel Vetter wrote: >> On Mon, Feb 02, 2015 at 03:30:21PM -0500, Rob Clark wrote: >> > On Mon, Feb 2, 2015 at 11:54 AM, Daniel Vetter <daniel at ffwll.ch> wrote: >> > >> My initial thought is for dma-buf to not try to prevent something than >> > >> an exporter can actually do.. I think the scenario you describe could >> > >> be handled by two sg-lists, if the exporter was clever enough. >> > > >> > > That's already needed, each attachment has it's own sg-list. After all >> > > there's no array of dma_addr_t in the sg tables, so you can't use one sg >> > > for more than one mapping. And due to different iommu different devices >> > > can easily end up with different addresses. >> > >> > >> > Well, to be fair it may not be explicitly stated, but currently one >> > should assume the dma_addr_t's in the dmabuf sglist are bogus. With >> > gpu's that implement per-process/context page tables, I'm not really >> > sure that there is a sane way to actually do anything else.. >> >> Hm, what does per-process/context page tables have to do here? At least on >> i915 we have a two levels of page tables: >> - first level for vm/device isolation, used through dma api >> - 2nd level for per-gpu-context isolation and context switching, handled >> internally. >> >> Since atm the dma api doesn't have any context of contexts or different >> pagetables, I don't see who you could use that at all. > > What I've found with *my* etnaviv drm implementation (not Christian's - I > found it impossible to work with Christian, especially with the endless > "msm doesn't do it that way, so we shouldn't" responses and his attitude > towards cherry-picking my development work [*]) is that it's much easier to > keep the GPU MMU local to the GPU and under the control of the DRM MM code, > rather than attaching the IOMMU to the DMA API and handling it that way. >
Keep in mind that I tried to reach you several times via mail and irc and you simply ignored me. Did you know that took almost all of your patches (with small changes)? And I needed to cherry pick you patches as they were a) wrong, b) solved in a different way or c) had "hack" in the subject. I am quite sorry that I ended that way, but it is not only my fault! > There are several reasons for that: > > 1. DRM has a better idea about when the memory needs to be mapped to the > GPU, and it can more effectively manage the GPU MMU. > > 2. The GPU MMU may have TLBs which can only be flushed via a command in > the GPU command stream, so it's fundamentally necessary for the MMU to > be managed by the GPU driver so that it knows when (and how) to insert > the flushes. > > > * - as a direct result of that, I've stopped all further development of > etnaviv drm, and I'm intending to strip it out from my Xorg DDX driver > as the etnaviv drm API which Christian wants is completely incompatible > with the non-etnaviv drm, and that just creates far too much pain in the > DDX driver. > That is bad, but life moves on. greets -- Christian Gmeiner, MSc https://soundcloud.com/christian-gmeiner
