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+The purpose of the changes described here is to implement a more general
+framework for multi-head on systems with more than one host-to-PCI bridge.
+The changes also implement a basic port of XFree86 to SPARC Solaris.
+
+These changes are derived from David S. Miller's submission #4653 to the
+patch list. David Andrew of Sun Microsystems was also kind enough to
+arrange for a hardware loan for development of these changes.
+
+These changes are known to work on several SPARC SunOS and UltraSPARC
+Linux configurations. Linux kernel work is in progress to port these
+changes to Linux/PowerPC.
+
+Several loose ends still need to be addressed before these changes can be
+considered stable. The bulk of this note is devoted to enumerating what
+remains to be done, along with other notes, broken down into various broad
+categories.
+
+SPARC SunOS (aka Solaris)
+-------------------------
+- An overview of this XFree86 port is available in README.Solaris.
+- The keyboard map code in hw/xfree86/os-support/sunos/sun_kbdEv.c needs
+ to be extended to handle more than only the sun5 keyboard I targeted it
+ for. Even for the sun5, the map is incomplete as several keys are not
+ mapped. What is there is just barely usable.
+- On exit, the server will zero out /dev/fb, but that might not be the
+ right thing to do for all primary adapters. This does however
+ appear to emulate the behaviour of Sun's commercial servers. It also
+ eliminates the need for output drivers to save and restore video memory
+ contents. (They still need to save/restore the mode timing however.)
+ This also chimes into a long-standing XFree86 policy to not save/restore
+ video memory contents if the mode on entry is found to be non-VGA, a
+ policy several existing drivers comply with.
+- The SBUS drivers (sunbw2, suncg14, suncg3, suncg6, sunffb, sunleo and
+ suntcx), the common layer's SBUS code and the fbdev driver have all
+ only been compile tested. There are likely to be Linux'isms within
+ them that remain to be dealt with.
+- It still needs to be verified whether or not this work adversely
+ affected support for ix86 Solaris.
+
+UltraSPARC Linux
+----------------
+- Although this code can be compiled using any Linux/SPARC64 kernel, it
+ can only run successfully using 2.4.12 or later.
+- I haven't had time to sufficiently dig into XKB to properly configure it
+ for sun5 keyboards. Given XFree86 on Linux/SPARC has been around for a
+ while, it's likely someone has already done this, and I'd appreciate
+ receiving a copy of a working XF86Config input section.
+
+PowerPC Linux
+-------------
+- As mentioned above, kernel work is in progress to port this PCI scheme
+ to Linux/PowerPC.
+- Aside from kernel work, the inX() and outX() definitions in compiler.h
+ will need to be changed to do something akin to their SPARC definitions,
+ i.e. consider their port argument to be a virtual address.
+
+Other Linux ports to multi-domain architectures
+-----------------------------------------------
+- Comments in os-support/bus/linuxPci.c document the kernel interface
+ required to port these changes. In short, Linux ports, such as Alpha
+ and mips, should follow SPARC and PowerPC's lead in providing support to
+ mmap() PCI devices through their /proc/bus/pci pseudo-files and to treat
+ such requests for host bridges as requests to mmap() space provided by
+ these bridges.
+
+Other OS's
+----------
+- In the right hands, either linuxPci.c or sparcPci.c can be used as a
+ guide for what would need to be done to port this scheme to other OS's.
+ Perhaps the largest difference between the two (in terms of interface to
+ the common layer) is that the SunOS port includes internally generated
+ domain numbers in PCITAG's, whereas the Linux port doesn't need to. The
+ remainder of the PCI code (which is OS-independent) can handle either
+ scheme.
+- Required entry points are xf86GetPciDomain(), xf86MapDomainMemory(),
+ xf86MapDomainIO() and xf86ReadDomainMemory(). Replacements for
+ xf86BusAccWindowsFromOS(), xf86PciBusAccWindowsFromOS() and
+ xf86AccResFromOS() might also be required.
+- Development of these changes has detected the fact that the XFree86 port
+ to the PowerMax OS is broken, and has been for some time, i.e. since
+ shortly after its introduction, back in the 3.9* days.
+
+SPARC PCI (OS-independent)
+--------------------------
+- The "Simba" PCI-to-PCI bridge used in SPARC's does not implement VGA
+ routing, as defined in the PCI specs. Fortunately, OpenPROM seems to
+ always route VGA resources to the bus with PCI connectors, but this also
+ causes the common layer to not mark any PCI adapter as primary.
+
+Multiple PCI domains (architecture- and OS-independent)
+-------------------------------------------------------
+- This implementation assumes every host-to-PCI bridge provides access to
+ a separate PCI domain. Each such domain provides three different
+ "address" spaces: PCI configuration, I/O and memory. The
+ implementation can also deal with situations where more than one PCI
+ domain share (different subsets of) the same PCI configuration space. I
+ have unconfirmed information that suggests it might be necessary to also
+ allow the sharing of PCI memory spaces.
+- This implementation also assumes the CPU's physical address space
+ includes the entirety of each domain's I/O and memory spaces. I know
+ this'll need to be changed to deal with the so-called UniNorth bridge,
+ found on PowerPC's, which allows access to only a subset of the memory
+ space behind it.
+- Ideally, the common layer should mark as primary up to one PCI adapter
+ per domain. This has yet to be done.
+- Something needs to be done about PCI master aborts on primary buses.
+ For details on this, see my long-winded diatribe in sparcPci.c, and
+ related comments in linuxPci.c. Suffice it to say here that I see the
+ eventual implementation of host bridge drivers within XFree86 as
+ unavoidable at this point.
+- DGA is broken on multi-domain platforms. The information passed to the
+ client to locate the framebuffer still needs to be revised. The best way
+ to deal with this is to change all drivers' OpenFramebuffer() function to
+ call a common layer routine to set the device name and displacements to be
+ returned to the DGA client.
+
+Output drivers
+--------------
+Most drivers currently used on ix86 need(ed) source code changes.
+- Calls to xf86ReadBIOS() and xf86MapVidMem() were replaced with calls to
+ xf86ReadDomainMemory() and xf86MapDomainMemory() respectively. Except
+ for the "ati" and "atimisc" modules, this has already been done.
+- All ix86-style I/O port numbers need to be declared as an IOADDRESS, a
+ type defined in xf86Pci.h as "unsigned long". Such port numbers also
+ need to be offset by a displacement which is also defined as an
+ IOADDRESS. Before a driver's PreInit() is called, the common layer
+ makes this displacement available in ScrnInfoRec.domainIOBase. For
+ single-domain architectures, such as ix86, domainIOBase will always be
+ zero. Current use of vgaHWRec.PIOOffset has also been adjusted
+ accordingly. Some drivers have been changed to keep a copy of this
+ displacement in their private structure. Internally, an IOADDRESS is
+ actually a pointer that has been recasted to an unsigned long, but the
+ common layer "hides" this fact from the driver ABI, which means that I/O
+ port numbers, as seen by drivers, remain as integers rather than
+ addresses. Aside from the ati and atimisc modules, s3, sis and tseng
+ are the only modules left whose I/O still needs to be converted (I've
+ temporarily run out of steam).
+- Note that these conversions are not necessarily sufficient to produce
+ drivers that will work on any given multi-domain architecture. A driver
+ that, for example, had endianness problems, still does. But, at least,
+ these conversions, along with the supporting common layer changes, make
+ PCI drivers more widely amenable to porting.
+- rdinx(), wrinx(), modinx(), testrg(), testinx() and testinx2() are not
+ given enough information to allow for the relocation of their I/O. They
+ are consequently being deleted. The apm and ark drivers, the only
+ remaining callers of the first three, have been changed to use local
+ definitions instead. The last three (test*()) were already unused.
+- As a temporary measure, these changes completely disable ISA-style
+ probing on SPARC's and PowerPC's. This means that driver calls to
+ xf86MatchIsaInstances(), while still valid, will always return detection
+ failure on SPARC's and PowerPC's. This will be dealt with when a more
+ general master abort handling scheme is implemented.
+- I need to make a decision about the master abort issues mentionned above
+ before I can convert the "ati" and "atimisc" modules. Consequently,
+ these modules still need to be compiled with -DAVOID_CPIO on
+ multi-domain architectures, and support for Mach64 variants as
+ non-primary heads is not yet available.
+
+$XFree86$