cpuid.4: Note which CPUs don't support CPUID and what happens

"Early 486" comes from an uncited wikipedia table, added in
<https://en.wikipedia.org/w/index.php?title=CPUID&diff=prev&oldid=592047209>
<https://en.wikipedia.org/w/index.php?title=CPUID&diff=prev&oldid=592047978>
but I spot-checked the rest of the table accurate to CPUs in my house
(the oldest of which is an original Celeron, so no 486),
and "early 486" is better than "early x86" which can mean anything.

This does leave earlier x86 unmentioned,
but Linux hasn't targeted those in over a decade,
so they're out of scope anyway.

Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Signed-off-by: Alejandro Colomar <alx@kernel.org>

diff --git a/man4/cpuid.4 b/man4/cpuid.4
index bd883e6d3d20be095d39935ef9d29ad4df1531c3..0b38fabe36db5e1c83bab6f0a189bbb939bef491 100644 (file)
--- a/man4/cpuid.4
+++ b/man4/cpuid.4
@@ -69,7 +69,9 @@ $ modprobe cpuid
 There is no support for CPUID functions that require additional
 input registers.
 .P
-Very old x86 CPUs don't support CPUID.
+Early i486 CPUs do not support the CPUID instruction;
+.\" arch/x86/kernel/cpuid.c cpuid_open()
+opening this device for those CPUs fails with EIO.
 .SH SEE ALSO
 .BR cpuid (1)
 .P