On 1/21/19 1:44 PM, Liam Mark wrote: > 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. > How can a client know that no CPU access has occurred that needs to be flushed out? > > 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
