--- Keith Whitwell <[EMAIL PROTECTED]> wrote: > Jon Smirl wrote: > > On Fri, 01 Oct 2004 18:05:29 +0100, Keith Whitwell > > <[EMAIL PROTECTED]> wrote: > > > >>>Second the DRM code always treats the framebuffer as if it is in > >>>IOMEM. But what about IGP type devices where the framebuffer is in > >>>main memory? These only exist on the x86 so treating their > framebuffer > >>>as IOMEM works since there is no difference between IOMEM and normal > >>>memory access on an x86. > >> > >>The framebuffer lives in agp memory on those devices, presumably this > is iomem > >>as it appears to be memory of the agp device. > > > > > > On normal AGP/PCI cards the memory is on the card. It is accessed over > > the AGP/PCI bus which requires special IO instructions on non-x86 > > hardware. IGP cards use the normal system memory for their buffers. > > You don't use the special IO instructions to access this memory. The > > key is where the memory lives, on the graphics card or on the > > motherboard. > > > > On x86 both types of memory use the same access instructions since the > > x86 makes AGP/PCI memory look like normal system memory. So we don't > > have a problem. > > I understand this. I'm pointing out that agp memory, ie. system memory > mapped > into the GART table, though it is backed by system memory, is typically > accessed through an io range of the gart device. So what sort of memory > is that? > Yes, thoguht it might help you better to view this IO port is a ?multi?point-to-point AGP bus. From the CPU, on the FSB, this memory as well as any other mmaped IO is accesed as system memory(with intructions like mov) and not IO-Ports that use in(asm) and out(asm) intructions.
> For the Intel chipsets, again, although the framebuffer is backed by > system > memory, all accesses to that memory are through a device io memory > range, not > by reading/writing to the backing memory directly. > "io memory range", still dosen't sound like an IO-Port(from the CPU's FSB PoV). This would most likely be memory-maped IO? > > On other platforms introduction of an IGP type device will break > > X/mesa since they don't know to switch from IO instruction access to > > normal memory access. IA64 may have already run into this on > > unreleased products since they have been asking questions along these > > lines. > > I've seen stuff on the web that suggests Intel wants to unify its > chipsets to > support both x86 and IA64, so that's not a huge suprise. It'd still be > good > to base any design on actual known examples rather than guesses as to > what > might be coming. > Good, lets talk about i386's ISA bus. Most every 16bit operation is still valid, the number of bits shoulden't be an issue. Port IO uses the same Address and Data bus as memory IO, the only difference being the PORTIO bit is 1(not 0 like with memeory reads/writes). When A program wishes to use PORTIO it must use the out(asm) and in(asm) instructions. All other IO is done with a multitude of other instructions. This is why mmaped IO is the way togo, there are more operations one can do with one instruction. To go one more layer up we start talking about "C". --- BOTOM LINE --- In C all memory access can be done with operators(like '='), wather it's a memory maped device or not. This is simply a product of the blocks on witch it's built. From C to asm to hardware buss, memory IO is not device(destination) specific. Port-io is the only other destination(port). We can change where memory IO goes by fideling with ports with our new fancy PCI bus, but this still dose not change the instructions(asm) or operators(C) that we use to access memory. > Keith > > > > ------------------------------------------------------- > This SF.net email is sponsored by: IT Product Guide on ITManagersJournal > Use IT products in your business? Tell us what you think of them. Give > us > Your Opinions, Get Free ThinkGeek Gift Certificates! Click to find out > more > http://productguide.itmanagersjournal.com/guidepromo.tmpl > -- > _______________________________________________ > Dri-devel mailing list > [EMAIL PROTECTED] > https://lists.sourceforge.net/lists/listinfo/dri-devel > __________________________________ Do you Yahoo!? Y! Messenger - Communicate in real time. Download now. http://messenger.yahoo.com ------------------------------------------------------- This SF.net email is sponsored by: IT Product Guide on ITManagersJournal Use IT products in your business? Tell us what you think of them. Give us Your Opinions, Get Free ThinkGeek Gift Certificates! Click to find out more http://productguide.itmanagersjournal.com/guidepromo.tmpl -- _______________________________________________ Dri-devel mailing list [EMAIL PROTECTED] https://lists.sourceforge.net/lists/listinfo/dri-devel
