Hi Mark, On Sat, Oct 26, 2019 at 07:54:40PM +0200, Sven Schnelle wrote: > Hi Mark, > > On Sat, Oct 26, 2019 at 10:35:20AM +0100, Mark Cave-Ayland wrote: > > > > However, the VRAM in Artist is not really exposed to the Host. Instead, > > > there's the Chipset inbetween that can do byte swapping (Colormap is LE, > > > VRAM is BE) and Bit-to-Byte/Word/Dword conversion. For example you could > > > write 0x55 into that VRAM region, and the chipset would expand that to > > > VRAM Bytes: 00 01 00 01 00 01 00 01. And to make it even worse emulation > > > wise it can also do different encodings for Read or Write accesses, and > > > mask out certain bits of the data. So after trying to convert it to the > > > "dirty bitmap" API i decided to just leave it as it is. The CPU load > > > used by the display update code is usually < 1%, so it's ok for me. > > > > Wow that sounds that some interesting hardware(!). Does it make sense to > > model the > > behaviour of the chipset separately using a proxy MemoryRegion similar to > > virtio i.e. > > introduce an intermediate IO MemoryRegion that does the swapping and then > > forward it > > onto the VRAM MemoryRegion? > > Thanks for the pointer, i'll check whether that would work. For now i > think i'll remove the Artist patch from the series, so we can apply the > other patches, and i'll re-submit Artist when it's done. I guess the > rewrite to use a MemRegion is a bit bigger. But i would to get the other > patches in especially the LASI Stuff as both Helge and i have a lot of > stuff depending on that.
I've looked into it again and changed my mind. There are at least the following functions that the Artist chip does before a Read/Write is passed to/from VRAM: - endianess conversion (actually configurable via some register, but i don't know how and hardwired it depending on CMAP / FB access) - The Address passed on the System bus are the X/Y coordinates added to the FB base address in the selected buffer instead of the VRAM offset for pixel data. I think that's configurable via the some registers, but i don't know how. Unfortunately there's absolutely no documentation about Artist available and everything was developed by reverse engineering. - bitmap to Byte/Word conversion (not implemented yet for the VRAM window, only for the I/O register window) So in my opinion it's way to much effort to squeeze all of that into the memory space, and it is not really a Memory range that's just behind a bus bridge. Regards Sven
