linux asm/barrier.h: Fix !MULTIPROCESSOR build.

drm: Eliminate __HAVE_ATOMIC_AS_MEMBAR conditionals.

Discussed on tech-kern:
https://mail-index.netbsd.org/tech-kern/2023/02/23/msg028729.html

branches: 1.19.4;
linux: Add alpha definitions of mb/wmb/rmb too for fun.

Who wants to plug an amdgpu into their alpha?

linux: Clarify error message in asm/barrier.h. Not just for drm.

linux: Add mips definitions for mb, wmb, rmb.

linux: Use dsb(sy/st/ld) from arm/cpufunc.h for mb/wmb/rmb.

Works on more Arm CPU types this way. From skrll.

drm: Fix missing barrier definitions on arm.

The definition will work on armv7; don't think we have any drmkms
drivers on armv<7.

drm: Comment *mb() vs smp_*mb() and omit default for *mb().

In general membar_*() is _not_ enough for *mb(), because membar_*()
is only for CPU/CPU synchronization on normal memory, and *mb()
requires machine-dependent I/O logic. Leave it as an `#error' case
if the architecture isn't listed here. But membar_*() is OK for
smp_*().

Fill in powerpc and sparc while here, as examples of what the
now-removed defaults failed to do. If you want to use drm on a mips
or alpha system yer gonna hafta fill this in yourself.

linux: Convert various API shims to use membar_release/acquire.

linux: Define mb/wmb/rmb as mfence/sfence/lfence on i386 too.

Not the same as membar_*; drm uses mb to order special instructions
like clflush which require mfence for ordering.

linux: For uniprocessor, define smp_*mb as __insn_barrier.

Otherwise ordering might not be guaranteed in the event of
preemption.

XXX pullup

linux: Eliminate read_barrier_depends, smp_read_barrier_depends.

These no longer exist in Linux; instead, Linux now uses READ_ONCE.

linux: Define mb/wmb/rmb for x86.

These are _not_ SMP barriers; on Linux they specifically mean
mfence/sfence/lfence. Although membar_sync and mb agree, and
membar_consumer and rmb agree, membar_producer and wmb _do not_ agree
on x86 -- Linux's wmb is specifically sfence, which is important only
for unusual memory types, whereas our membar_producer is limited to
ordinary memory.

Use adequate memory barrier for load-acquire semantics.

It is unfortunate that we chose the name membar_enter to have the
wrong semantics for this.

Move smp_mb_before/after_atomic from linux/atomic.h to asm/barrier.h.

Side-load linux/compiler.h in asm/barrier.h.

Fix mb/wmb/rmb on aarch64 to use dsb instead of dmb.

For module build assume multiprocessor.

branches: 1.3.2; 1.3.4; 1.3.6;
keep dsb in vchiq code.

dsb refers to an arm instruction, so it won't be used on MI code.

add dsb macro from vchiq

Move barrier to common so it can be shared with vchiq

linux: Make WARN_ONCE actually happen only once.

linux: Move BUILD_BUG_* to common linux/build_bug.h.

Make BUILD_BUG_ON_INVALID work on bit-field expressions.

Move linux/bug.h and asm/bug.h to common.

Define Linux byte order macros __BIG_ENDIAN/__LITTLE_ENDIAN.

branches: 1.1.2; 1.1.6;
Missed a drm2 -> common move.

branches: 1.1.2; 1.1.6;
Fix undoing of -Wpointer-arith workaround.

linux asm/vmware.h: Fill this in with hypercall asm.

Not sure if it's necessary to support vmcall or vmmcall -- if so,
need to deal with binary patching inline asm, ugh.