Messages in this thread | | | Date | Wed, 25 Jun 2008 18:18:04 -0700 | From | Jeremy Fitzhardinge <> | Subject | Re: kmap_atomic_pfn for PCI BAR access? |
| |
Keith Packard wrote: > The graphics memory BAR is generally fairly good sized; on Intel chips, > it's between 256M and 1G (and growing). I want to write data into this > region from kernel space, but it's really too big to map the whole thing > into kernel address space, especially on 32-bit systems. ioremap is not > a good option here -- it's way too slow. > > With CONFIG_HIGHMEM enabled, I can use kmap_atomic_pfn (well, actually > the kmap_atomic_proc_pfn included in the DRM tree) and things work quite > well -- performance is good, with barely any measurable time spent in > the PTE whacking (~1%). > > However, with CONFIG_HIGHMEM disabled, there aren't any PTEs reserved > for this kind of mapping fun. This makes me suspect that abusing > kmap_atomic for this operation would not be appreciated. > > Should I use kmap_atomic_pfn to reach my PCI BAR like this? > > Would it be reasonable to supply a patch that made this work even > without CONFIG_HIGHMEM? >
Usually people use ioremap to map device memory. Wouldn't that work in this case?
J
| |