linux-kernel - Re: What pokes the ISA IO port of 0x211 ?

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Message-ID: <480F456D.3680.ACD58B03@localhost>
Date:	Wed, 23 Apr 2008 14:19:25 +0200
From:	"Frantisek Rysanek" <Frantisek.Rysanek@...t.cz>
To:	linux-kernel@...r.kernel.org
Subject: Re: What pokes the ISA IO port of 0x211 ?

On 21 Apr 2008 at 19:40, H. Peter Anvin wrote:
> It might be easiest to put in a hack in the kernel by hacking
> outb/outw/outl and print stack trace when called when trying to poke
> this port. 

On 21 Apr 2008 at 22:34, Rene Herman wrote:
> Ah, it's the old analog gameport: ns558_init.

Well my immediate initial idea was indeed the game port, 
IO port 0x201 immediately started jumping up and down 
in the dark recesses of my memory from teenage years,
when I was trying this and that in Borland C in DOS...

So even before I wrote to LKML, I went into "make menuconfig"
and made sure that any entries related to the game port
were disabled:

Device Drivers -->
 Input device support -->
  Joystick interface = disabled
  Joysticks/Gamepads = disabled

I've been having all of that disabled in my kernel for ages,
I haven't met a game port since I abandoned my 486+SB16.

So, after Rene's response and HPA's responses, I resorted to
the suggested hacking on include/asm/io.h . 

After some grepping through the kernel sources, I could come up
with a simple call to dump_stack(). I added
  if (port == 0x211) dump_stack();\
into <asm/io.h>, on a second line below
  #define BUILDIO(bwl,bw,type)
into the definition of
  static inline void out##bwl##_local()
That gave me a linker error in the final stages of "make bzImage".
Clearly arch/i386/boot/compressed/misc.c doesn't get linked
directly to the rest of the kernel binary image, so it doesn't
have access to the kernel's symbols.
I solved that by making a clipboard copy of the whole huge BUILDIO 
"template" macro definition and wrapping the first copy in an 
  #ifndef SKIP_STACK_DUMP 
and I only defined SKIP_STACK_DUMP in compressed/misc.c
to avoid the linking problem...

Much to my amazement, this time it worked, 
and I was even more amazed to find out, that in fact 
Rene Herman was right :-)))

The poke is indeed performed by a function called ns558_init
and it's indeed related to the generic game port.

What I missed in the menuconfig was this entry:

Device Drivers -->
 Input device support -->
  Hardware I/O ports -->
   Gameport support -->
    Classic ISA and PnP gameport support

Also known as CONFIG_GAMEPORT_NS558, which enables compilation of 
drivers/input/gameport/ns558.c

It's always fun to learn about multiple menuconfig entries
for the same piece hardware or functionality in general :-)

Thanks to all those who replied, thanks for your time,
and have a nice, productive day :-)

Frank Rysanek

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