Re: i8042 access timings

[Randy.Dunlap]

Vojtech Pavlik wrote:
> On Fri, Jan 28, 2005 at 04:20:58PM +0200, Jaco Kroon wrote:
>
> > Vojtech Pavlik wrote:
> >
> > > On Thu, Jan 27, 2005 at 09:29:47PM +0100, Andries Brouwer wrote:
> > >
> > >
> > >
> > > > > So what _might_ happen is that we write the command, and then 
> > > > > i8042_wait_write() thinks that there is space to write the data 
> > > > > immediately, and writes the data, but now the data got lost because the 
> > > > > buffer was busy.
> > > >
> > > > Hmm - I just answered the same post and concluded that I didnt understand,
> > > > so you have progressed further. I considered the same possibility,
> > > > but the data was not lost since we read it again later.
> > > > Only the ready flag was lost.
> > >
> > >
> > > What I believe is happening is that we're talking to SMM emulation of
> > > the i8042, which doesn't have a clue about these commands, while the
> > > underlying real hardware implementation does. And because of that they
> > > disagree on what should happen when the command is issued, and since the
> > > SMM emulation lazily synchronizes with the real HW, we only get the data
> > > back with the next command.
> > >
> > > I still don't have an explanation why both 'usb-handoff' and 'acpi=off'
> > > help, I'd expect only the first to, but it might be related to the SCI
> > > interrupt routing which isn't done when 'acpi=off'. Just a wild guess.
> >
> > Ok, I'm not too clued up with recent hardware and the BIOS programming 
> > that goes with it (being a system admin/application programmer), what 
> > exactly is usb-handoff?
>
>
> usb-handoff is a kernel option that enables a PCI quirk routine that
> takes the USB controller out of BIOS's hands. Until that is done (the
> linux USB drivers also do it, only later), the BIOS owns the USB
> controller and tries to emulate a PS/2 mouse and keyboard for systems
> which can't handle USB.
>
>
> > acpi=off obviously just turns all acpi support 
> > in the kernel off. 
>
>
> Indeed.
>
>
> > SCI is also a new abbreviation I haven't seen 
> > before.
>
>
> System Configuration Interrupt. In addition to SMI (System Management
> Interrupt), these are two interrupts the BIOS uses to do its job behind
> the operating system's back.

ACPI 2.0 spec says:
System Control Interrupt (SCI)
A system interrupt used by hardware to notify the OS of ACPI events. 
The SCI is an active, low, shareable, level interrupt.

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