On Wed, Jun 06, 2012 at 02:10:34PM -0700, Colin Cross wrote:
On Fri, May 11, 2012 at 5:17 PM, Anton Vorontsov anton.vorontsov@linaro.org wrote:
This includes devices' memory (e.g. framebuffers or memory mapped EEPROMs on a local bus), as well as the normal RAM that we don't use for the main memory.
For the normal (but unused) ram we could use kmaps, but this assumes highmem support, so we don't bother and just use the memory via ioremap.
As a side effect, the following hack is possible: when used together with pstore_ram (new ramoops) module, we can limit the normal RAM region with mem= and then point ramoops to use the rest of the memory, e.g.
mem=128M ramoops.mem_address=0x8000000
Sure, we could just reserve the region with memblock_reserve() early in the arch/ code, and then register a pstore_ram platform device pointing to the reserved region. It's still a viable option if platform wants to do so.
Also, we might want to use IO accessors in case of a real device, but for now we don't bother (the old ramoops wasn't using it either, so at least we don't make things worse).
This is long merged, but I remembered why I moved away from using ioremap. The current code uses atomics to track the ringbuffer positions, which results in ldrex and strex instructions on ARM. ldrex and strex on memory that is mapped as Device memory (which is what ioremap maps as) is implementation defined, and is unpredictable at the architecture level.
Makes sense, thanks for sharing! Fortunately, we still map things w/ vmap if pfn appears to be valid. :-)
Thanks,