[PATCH-for-9.0] hw/i386/pc: Deprecate 64-bit CPUs on ISA-only PC machine

[Philippe Mathieu-Daudé]

Per Daniel suggestion [*]:

 > isapc could arguably be restricted to just 32-bit CPU models,
 > because we should not need it to support any feature that didn't
 > exist prior to circa 1995. eg refuse to start with isapc, if 'lm'
 > is present in the CPU model for example.

[*] ZgQkS4RPmSt5Xa08@redhat.com/">https://lore.kernel.org/qemu-devel/ZgQkS4RPmSt5Xa08@redhat.com/

Suggested-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
---
 docs/about/deprecated.rst | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/docs/about/deprecated.rst b/docs/about/deprecated.rst
index 7b548519b5..345c35507f 100644
--- a/docs/about/deprecated.rst
+++ b/docs/about/deprecated.rst
@@ -208,6 +208,13 @@ is no longer packaged in any distro making it harder to 
run the
 ``check-tcg`` tests. Unless we can improve the testing situation there
 is a chance the code will bitrot without anyone noticing.
 
+64-bit (x86_64) CPUs on the ``isapc`` machine (since 9.0)
+'''''''''''''''''''''''''''''''''''''''''''''''''''''''''
+
+The ``isapc`` machine aims to emulate old PC machine without PCI was
+generalized, so hardware available around 1995, before 64-bit intel
+CPUs were produced.
+
 System emulator machines
 ------------------------
 
-- 
2.41.0