On Mon, Dec 5, 2016 at 10:02 AM, Jason Gunthorpe <jgunthorpe@xxxxxxxxxxxxxxxxxxxx> wrote: > On Mon, Dec 05, 2016 at 09:40:38AM -0800, Dan Williams wrote: > >> > If it is kernel only with physical addresess we don't need a uAPI for >> > it, so I'm not sure #1 is at all related to iopmem. >> > >> > Most people who want #1 probably can just mmap >> > /sys/../pci/../resourceX to get a user handle to it, or pass around >> > __iomem pointers in the kernel. This has been asked for before with >> > RDMA. >> > >> > I'm still not really clear what iopmem is for, or why DAX should ever >> > be involved in this.. >> >> Right, by default remap_pfn_range() does not establish DMA capable >> mappings. You can think of iopmem as remap_pfn_range() converted to >> use devm_memremap_pages(). Given the extra constraints of >> devm_memremap_pages() it seems reasonable to have those DMA capable >> mappings be optionally established via a separate driver. > > Except the iopmem driver claims the PCI ID, and presents a block > interface which is really *NOT* what people who have asked for this in > the past have wanted. IIRC it was embedded stuff eg RDMA video > directly out of a capture card or a similar kind of thinking. > > It is a good point about devm_memremap_pages limitations, but maybe > that just says to create a /sys/.../resource_dmableX ? > > Or is there some reason why people want a filesystem on top of BAR > memory? That does not seem to have been covered yet.. > I've already recommended that iopmem not be a block device and instead be a device-dax instance. I also don't think it should claim the PCI ID, rather the driver that wants to map one of its bars this way can register the memory region with the device-dax core. I'm not sure there are enough device drivers that want to do this to have it be a generic /sys/.../resource_dmableX capability. It still seems to be an exotic one-off type of configuration. -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
