* Alan Cox <[email protected]> wrote:
> For modern systems we should just use tsc delays, but we have to fix
> all the drivers first as right now 0x80 causes posting and we have
> some PCI users (I think probably all bogus), and we need to fix the
> tons of locking errors that are mostly covered by the inb 0x80 being
> an indivisible operation so not getting split by interrupts/SMP.
i dont get your last point. Firstly, we do an "outb $0x80" not an inb.
Secondly, outb $0x80 has no PCI posting side-effects AFAICS. Thirdly,
even assuming that it has PCI posting side-effects, how can any locking
error be covered up by an outb 0x80 sticking together with the inb it
does before it? The sequence we emit is:
inbb $some_port
outb $0x80
and i see that the likelyhood of getting such sequences from two CPUs
'mixed up' are low, but how can this have any smp locking side-effects?
How can this provide any workaround/coverup?
> I've been going through the drivers that use it - the biggest mess
> appears to be in the watchdog drivers all of which copied an original
> lack of locking from the mid 1990s caused by umm.. me. I guess my past
> is catching up with me ;)
heh :-)
> The X server also appears to touch 0x80 in some cases but we can hope
> only on ancient hardware.
do you have any memories about the outb_p() use of misc_32.c:
pos = (x + cols * y) * 2; /* Update cursor position */
outb_p(14, vidport);
outb_p(0xff & (pos >> 9), vidport+1);
outb_p(15, vidport);
outb_p(0xff & (pos >> 1), vidport+1);
was this ever needed? This is so early in the bootup that can we cannot
do any sensible delay. Perhaps we could try a natural delay sequence via
inb from 0x3cc:
outb(14, vidport);
inb(0x3cc); /* delay */
outb(0xff & (pos >> 9), vidport+1);
inb(0x3cc); /* delay */
outb(15, vidport);
inb(0x3cc); /* delay */
outb(0xff & (pos >> 1), vidport+1);
inb(0x3cc); /* delay */
as a dummy delay (totally untested).
Reading from the 0x3cc port does not impact the cursor position update
sequence IIRC - i think the vidport is even ignored for the input
direction by most hardware, there's a separate input register. The 0x3cc
port is a well-defined VGA register which should be unused on non-VGA
hardware. (which makes it a perfect delay register in any case)
Ingo
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