On Thu, May 27, 2010 at 12:22:35AM -0600, Robert Hancock wrote:
quoted text
> On 05/13/2010 10:54 AM, Linus Torvalds wrote:
> >
> >
> >On Thu, 13 May 2010, Dmitry Torokhov wrote:
> >>
> >>Apple does proper thing in BIOS and omits keyboard and mouse PNP
> >>devices, but because of other players we do not really trust PNP BIOS
> >>and resort to banding on ports directly - there are cases when box has
> >>mouse and/or keyboard but they are not present in BIOS. Damed if you do,
> >>damned if you don't...
> >
> >Umm. No.
> >
> >PnP information _commonly_ doesn't inclure PS/2 ports, even when they
> >exist. Lack of PnP information about the keyboard port means absolutely
> >nothing, and anybody who tells you otherwise is totally and utterly wrong.
> >
> >So don't confuse this with PnP issues. That's a total red herring, and
> >Apple is _not_at_all_ "doing the proper thing in the BIOS".
> >
> >Quite the reverse. Apple is very clearly doing something horribly _wrong_
> >in their BIOS. Don't give them kudos for being incompetent morons.
> 
> I don't think they did anything wrong in their BIOS, it's working
> exactly as the spec intended. There is no PS/2 controller, and the
> ACPI PnP tables do not list one. I wouldn't argue that it was a good
> decision of them to have the hardware somehow blow up if something
> poked those ports anyway, but from a BIOS point of view they did the
> right thing.
> 
> >
> >Just google for
> >
> >	"Probing ports directly" "i8042 KBD port"
> >
> >and you'll get a lot of hits. That's not because those machines have wrong
> >PnP tables - it's because fundamentally PNP is a joke, and on PC's what is
> >much more important is "standard IO ports".
> >
> >For example, in that thread, Bastien is quoted:
> >
> >	>  In other words, on x86, if PNP and/or ACPI don't indicate any PS/2
> >	>  controller exists, we randomly bang on the ports in the expectation
> >	>  they'll be there anyway. This seems rather misguided.
> >
> >and all that tells me is that Bastien doesn't know what he is doing. It is
> >_not_ "randomly bang" - it's called standard PC hardware.  And it's not
> >"misguided" - it's very much correct and required, exactly because PnP
> >itself is the misguided aborted fetus of a braindamaged mind.
> 
> I think that may have been me, actually, not Bastien. Misguided may
> have been a too strong term, but in this case I think the PnP
> information is quite trustable because Windows trusts it. Definitely
> for the PS/2 mouse controller (quite likely the keyboard too), if
> Windows is in ACPI mode and the PnP tables do not list it, it will
> not detect or use it.
> 
> Now, many BIOSes seem to have have code (like an "auto" mode for the
> PS/2 port, which may or may not be always set) which disables the
> PnP entry if it doesn't detect a mouse or keyboard connected on
> boot. If memory serves, this is because I think at least on some
> versions, if Windows finds a controller but no mouse is responding
> then it shows up with an error indication in Device Manager, which
> tends to make people unhappy. This is likely what's responsible for
> most of those cases where Linux detects devices after "probing ports
> directly", because the BIOS hid the device but we were too "clever"
> for it and found it anyway.
> 
> In fact on a lot of boards, Linux still detects the port even if set
> as "disabled" in the BIOS, because all that does is disable the PnP
> entry.
> 
> Long and the short of it is, it seems pretty safe to say that on any
> ACPI machine, if there's no PnP entry for PS/2 devices, the BIOS
> does not intend for the OS to use them. There may be cases where you
> might want to try to locate ports anyway (maybe you really want to
> hotplug a mouse in after boot, or you have an ancient KVM which
> doesn't emulate a device presence on the non-selected machine), but
> those seem like very much the exception rather than the rule.
>

I would be much more happy if ACPI would add devices to the device tree
even if they happen to be disabled. Then we could really trust DSDTs and
not bang i8042 ports if the controller is truly not there (newer Dell
servers, Apple, etc) but still woudl detect the controller just fine if
BIOS decided to hide it from Windows.

-- 
Dmitry
--
unsubscribe notice
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/