On Wed, 2002-04-24 at 14:13, Jens Owen wrote: > ... > > Jose, > > I don't have a complete answer for you, but here is *some* background > information that might help. > > The drmAddBufs style was created with the origianal DRI infrastructure > that supported a partial implementation of the Gamma driver. Buffers > were short, and based out of PCI memory. > > The first complete driver was the 3Dfx. It used MMIO and didn't need > any DMA buffers. > > The second and third complete drivers were the i810 and mga. The were > the first to require AGP based DMA, and that's when the drmAGPAlloc > functionality was added. > > I believe the AGP implementation is flexable about where the physical > pages reside, and can use the GART to make the pages appear contiguous > to both the 3D driver *and* the hardware. > > For PCI DMA, I believe you need to allocate actual contiguous pages in > order for the hardware to see the memory as contiguous. This may be why > the mechanism is more cumbersome--or it could be that the PCI DMA case > just hasn't been fully flushed out.
Allocating contiguous pages in physical memory is complicated, and is addressed by the drmAddBufs, assuming that one doesn't choose the size of each individual buffer too big. The problem is that drmAddBufs makes it difficult to separate the general purpose DMA buffers from buffer with a special purpose, such as primary buffers or page tables. I think I'll extract the actual buffer allocation code from drmAddBufs into a separate IOCTL available for those cards that may need it. > I believe the r128 driver's PCI support still utilizes GART > functionality to allow non-contiguous memory to be utilized. Your > driver may be the first to need true PCI support, and *possibly* the > last to need it unless other legacy chipsets of the same era are > supported. The gamma driver could use it (but just to have a little more code readability). I don't know if MGA has a PCI version but it would simplify substantially extending its support in case there is, as there would be possible to make a parallelism between the AGP and PCI code. I believe that the Savage chips come in PCI versions too, and this might be handy again. > > I hope this helps. Yes. Thanks very much for the background info. > > -- /\ > Jens Owen / \/\ _ > [EMAIL PROTECTED] / \ \ \ Steamboat Springs, Colorado > Regards, Jose Fonseca _______________________________________________ Dri-devel mailing list [EMAIL PROTECTED] https://lists.sourceforge.net/lists/listinfo/dri-devel
