Den 13.02.2019 02.44, skrev Rob Herring: > On Tue, Feb 12, 2019 at 7:00 PM Eric Anholt <eric@xxxxxxxxxx> wrote: >> >> Rob Herring <robh@xxxxxxxxxx> writes: >> [snip] >>> FWIW, I'm working on the panfrost driver and am using the shmem >>> helpers from Noralf. It's the early stages though. I started a patch >>> for etnaviv to use it too, but found I need to rework it to sub-class >>> the shmem GEM object. >> >> Did you just convert the shmem helpers over to doing alloc_coherent? If >> so, I'd be interested in picking them up for v3d, and that might help >> get another patch out of your stack. > > I haven't really fully addressed that yet, but yeah, my plan is just > to switch to WC alloc and mappings. I was going to try to make it > configurable, but there is a comment in the ARM dma mapping code which > makes me wonder if tinydrm using streaming DMA for SPI is > fundamentally broken (and maybe CMA is less broken?). If not broken, > not guaranteed to work. > > /* > * The whole dma_get_sgtable() idea is fundamentally unsafe - it seems > * that the intention is to allow exporting memory allocated via the > * coherent DMA APIs through the dma_buf API, which only accepts a > * scattertable. This presents a couple of problems: > * 1. Not all memory allocated via the coherent DMA APIs is backed by > * a struct page > * 2. Passing coherent DMA memory into the streaming APIs is not allowed > * as we will try to flush the memory through a different alias to that > * actually being used (and the flushes are redundant.) > */ > Thanks for drawing my attention to this, I wasn't aware of it. Sadly the SPI subsystem doesn't have a way to pass in dma buffers, everything has to go through the streaming API. Long term I guess I have to add support for that. Noralf. _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
