On Mon, May 21, 2012 at 06:40:38PM +0000, Blue Swirl wrote: > On Mon, May 21, 2012 at 6:28 PM, Peter Maydell <peter.mayd...@linaro.org> > wrote: > > On 21 May 2012 19:08, Blue Swirl <blauwir...@gmail.com> wrote: > >> On Mon, May 21, 2012 at 10:36 AM, Peter Maydell > >> <peter.mayd...@linaro.org> wrote: > >>> I think it would be nice to have this in upstream qemu; however adding > >>> transaction properties to the IO interface would be quite tricky I > >>> suspect... > >> > >> This is limited to CPU and CPU local bus devices (not generic like > >> PCI), so there could be an out of band mechanism to get/set the > >> additional data. > > > > What's your definition of "generic" here? AMBA isn't particularly > > limited to CPU local bus devices either, really (for instance > > the connection between a versatile express CPU daughterboard > > and the motherboard includes an AMBA AXI bus). > > I'd expect that only AMBA devices (ARM specific) would care about the > properties, while for example NE2k could not care less. > > > > >> For example store in op_helper.c could use > >> cpu_set_amba_properties(...) before the store and afterwards > >> cpu_get_amba_reply(...). > > > > We really don't want to do two helper function calls for every > > load or store! If you're going to implement them at all then > > you need a more efficient implementation than that... > > How about lazy evaluation: generate the properties/evaluate reply only > if the device wants them via > device_get_properties()/device_set_reply(). Then the transaction > overhead could be ignored by everyone if not needed.
Hi, This party came up when evaluating the mem API. IMO, it would be nice to have a way for the master (CPU, DMA or whatever) to be able to pass attributes with accesses. Possibly also for the device to return return codes (or error codes) as a result of the access. The details may be bus specific (AMBA, OCP, etc) but the concept is not. Unfortunately, I'm afraid it would involve quite a bit of changes to the code again unless someone comes up with a smart way of doing it... Cheers
