On Thu, Aug 05, 2010 at 06:43:50AM -0700, Anoop P.A. wrote: > With a slightly modified patched (copied below) I have reached a point > where I am no more seeing errors like segmentation fault, bus error > (which was due to memory corruption I believe). > How ever I am still seeing some kind of file corruption. > > I believe this file corruption happening because cache is not getting > invalidated before a highmem dma. I am not sure which routine to call to > invalidate cache for a highmem address. Since you're running on an RM9000 class CPU, why don't just use a 64-bit kernel? Highmem is just so f*cking insane that you want to avoid it like French kisses from a zombie suffering ebola. If you have DMA restrictions then you may consider reusing ZONE_DMA. That said, a word on the history of the MIPS highmem code. It was written for a company who in the early stages of the 64-bit kernel didn't want to be the first through the minefield in 2001. That CPU had full coherency and no cache aliases so arch/mips/mm/dma-*.c did not need any code to support it at all and for many years after that everybody either had a small 32-bit system that didn't need highmem or went 64-bit right away so the gaps in the code while well known were never fixed up ... I'm a bit surprised that the patch posted actually made things work better for you since it entirely avoids flushing of highmem pages. The code as it was originally written using page_address() will perform cacheflushes for highmem pages as well - but only for highmem pages are actually are mapped. That is your code will flush less pages than the existing code. Ralf
