On Mon, 21 Jan 2019, Christoph Hellwig wrote: > On Sat, Jan 19, 2019 at 08:50:41AM -0800, Laura Abbott wrote: > > > And who is going to decide which ones to pass? And who documents > > > which ones are safe? > > > > > > I'd much rather have explicit, well documented dma-buf flags that > > > might get translated to the DMA API flags, which are not error checked, > > > not very well documented and way to easy to get wrong. > > > > > > > I'm not sure having flags in dma-buf really solves anything > > given drivers can use the attributes directly with dma_map > > anyway, which is what we're looking to do. The intention > > is for the driver creating the dma_buf attachment to have > > the knowledge of which flags to use. > > Well, there are very few flags that you can simply use for all calls of > dma_map*. And given how badly these flags are defined I just don't want > people to add more places where they indirectly use these flags, as > it will be more than enough work to clean up the current mess. > > What flag(s) do you want to pass this way, btw? Maybe that is where > the problem is. > The main use case is for allowing clients to pass in DMA_ATTR_SKIP_CPU_SYNC in order to skip the default cache maintenance which happens in dma_buf_map_attachment and dma_buf_unmap_attachment. In ION the buffers aren't usually accessed from the CPU so this allows clients to often avoid doing unnecessary cache maintenance. Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
