On Tue, Sep 01, 2009 at 03:35:15PM +0200, Ameya Palande wrote: > Hi, > > Current DSPBridge MPU side API provides following IOCTLs which are related to > reserving and mapping DSP address space: > > 1. DSPProcessor_ReserveMemory(): Reserve a virtually contiguous region of DSP > address space. > 2. DSPProcessor_Map(): Maps an MPU buffer to the DSP virtual address space. > 3. DSPProcessor_UnMap(): Remove an MPU buffer mapping from the DSP virtual > address space. > 4. DSPProcessor_UnReserveMemory(): Frees a previously reserved region of the > DSP virtual address space. > > Typical call sequence is: > > DSPProcessor_ReserveMemory() > DSPProcessor_Map() > DSPProcessor_UnMap() > DSPProcessor_UnReserveMemory() > > Current approach has following problems: > 1. Caller has to perform 4 system calls in order to map and unmap a buffer. > 2. Kernel has no idea about the type of buffer (input/output). So depending > on buffer type caller has to explicitly call DSPProcessor_FlushMemory() or > DSPProcessor_InvalidateMemory(). > > Proposed approach: > Introduce 2 new IOCTLs which combine (reserve, map) and (unmap, unreserve). > Caller should also specify buffer type (input/output) attribute as a > parameter to new mapping IOCTL. > > Benefits of new approach: > 1. Saves 2 system calls per map and unmap pair. > 2. By implementing lazy unreserve we can introduce cache of reserved > mappings, which can skip reserve, unreserve operations. > 3. Kernel can take care of flushing/invalidating cache depending on buffer > type, which saves system call overhead and removed explicit cache control > from user space. > > These IOCTLs can be added to the current set of API which doesn't break > compatibility with old applications. > > Waiting for comments! > > Ideas proposed in this document are from: > 1. Hiroshi Doyu <hiroshi.doyu@xxxxxxxxx> > 2. Felipe Contreras <felipe.contreras@xxxxxxxxx> The whole proposal looks good to me :) However, sometimes you would still want to do some extra cache operations afer Map() there should be a way to do 'flush', 'clean' and 'inv'. Cheers. -- Felipe Contreras -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
