On Mon, Oct 01, 2007 at 10:04:32AM +0100, veerasena reddy wrote: > I have ported Linux-2.6.18 kernel on MIPS24KE > processor. I am using write back cache policy. > > Could you please guide me under what cases the below > cache API's are being used: > - dma_cache_wback_inv() : Could you explain what > exactly this function does > - dma_cache_wback() : This function write back the > cache data to memory > - dma_cache_inv : This function invalidate the cache > tags. so subsequent access will fetch from memory. > > Once I looked the above function definitions in > linux-2.6.18/arch/mips/mm/c-r4k.c. > All these function's implemetation are same except > bc_wbak_inv() is called in both dma_cache_wback-inv() > and dma_cache_wback(), where as bc_inv() is called in > case of dma_cache_inv. > > Also, bc_inv()/bc_wbak_inv are define as null > implementation for R4000. > That means all three functions are doing same > functionality in case of R4000. > > What are the difference between these three functions. > Under what cases these functions are used. An internal only interface to be used with I/O cache coherency. > Please guide me if you have any links which will > explain these API's. Easy answer, don't use them, for 2.6.24 I've queued a patch to kill this API. Documentation/DMA-API.txt documents how to properly deal with I/O coherency in Linux. Ralf
