IO_DELAY documentation

From: George Spelvin
Date: Sun Feb 17 2008 - 20:21:20 EST


"make oldconfig" doesn't know how to display the per-item help, so
something like this is needed. It was a squeeze to make all the help
text, plus option prompt, fit into 24 lines. If you think that's not
a concern, some of the wording could be improved.

(Added text placed into the public domain; copyright abandoned.)

diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug
index 864affc..8e2ceb6 100644
--- a/arch/x86/Kconfig.debug
+++ b/arch/x86/Kconfig.debug
@@ -157,6 +157,24 @@ config IO_DELAY_TYPE_NONE
choice
prompt "IO delay type"
default IO_DELAY_0XED
+ help
+ The original IBM PC required short pauses between consecutive
+ accesses to its peripheral chips. This can be provided four ways:
+
+ * A dummy write to port 0x80 has been used for 15 years, but
+ crashes the AMD64-based HP dv9000z laptop. The safest option.
+ * Port 0xED is also believed safe, and testing is requested.
+ * Udelay is awkward to implement in the kernel due to processor
+ speed variations, but should be extremely safe.
+ * All but the very oldest PCs use emulations of the original
+ peripheral chips built into a "Super I/O" chip, and usually
+ do no need the delay at all. The most efficient option.
+
+ On the majority of machines, all four options should work.
+ If you have a computer on which any of the four options
+ (especially _0XED or _NONE) does not work, please report it,
+ with a detailed description of the motherboard (and "lspci -nn"
+ and "dmidecode" output), to linux-kernel@xxxxxxxxxxxxxxxx

config IO_DELAY_0X80
bool "port 0x80 based port-IO delay [recommended]"
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