On Mon, Oct 24, 2016 at 04:31:45PM +1000, Dave Airlie wrote: > A recent change to the mm code in: > 87744ab3832b83ba71b931f86f9cfdb000d07da5 > mm: fix cache mode tracking in vm_insert_mixed() > > started enforcing checking the memory type against the registered list for > amixed pfn insertion mappings. It happens that the drm drivers for a number > of gpus relied on this being broken. Currently the driver only inserted > VRAM mappings into the tracking table when they came from the kernel, > and userspace mappings never landed in the table. This led to a regression > where all the mapping end up as UC instead of WC now. Eek. > I've considered a number of solutions but since this needs to be fixed > in fixes and not next, and some of the solutions were going to introduce > overhead that hadn't been there before I didn't consider them viable at > this stage. These mainly concerned hooking into the TTM io reserve APIs, > but these API have a bunch of fast paths I didn't want to unwind to add > this to. > > The solution I've decided on is to add a new API like the arch_phys_wc > APIs (these would have worked but wc_del didn't take a range), and > use them from the drivers to add a WC compatible mapping to the table > for all VRAM on those GPUs. This means we can then create userspace > mapping that won't get degraded to UC. Is anything on a driver to be able to tell when this is actually needed ? How will driver developers know? Can you add a bit of documentation to the API? If its transitive towards a secondary solution indicating so would help driver developers. Luis _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
