Etienne Lorrain wrote:
> --- "H. Peter Anvin" <[email protected]> wrote:
>> Chuck Ebbert wrote:
>
> Wrong name.
>
>>>> Have fun, this code:
>>>> - do not open the fast A20 gate before checking if the slow A20 gate is open or
>> closed.
>>
>> As does the current code; this is highly intentional behaviour since
>> there are machines (in particular a whole series of machines made by
>> Olivetti) which lock up if you do it differently.
>
> There was some discussion on this list about some machine which would not wake-up
> correctly if slow A20 was not closed, long time ago. I did not really follow
> the code after that discussion.
> I wonder if you should do a "outb(0xFF, 0x64);" after "outb(0xdf, 0x60);" like
> the HIMEM.SYS driver, to force an immediate update of the I/O ports - I think
> I also read that in this initial chip docs, long time ago also.
Well, the code we have now has worked for quite some years as-is. This
code is not an algorithmic change. I haven't seen any machines which
need outb(0xff, 0x64) -- I wonder if that has the same effect as our
io_delay() or if it is actually potent. I shall look into it.
>>>> - Does not save and restore %ds when printing a char on the screen (%ds is
>>>> destroyed only when the content of the screen scroll - only for some video cards)
>> %ds? Aren't you confusing it with the old bug which would destroy %bp?
>> If you have any references to %ds being destroyed I would be very
>> surprised. I can guarantee that very little if any assembly code I've
>> ever seen that deals with INT 10h -- and I've seen a lot of it -- guards
>> against %ds being randomly trashed.
>>
>> However, the trashing of %bp is a well-known bug (although only for
>> machines older than the ones that can run Linux) -- the Interrupt List has:
>>
>> BUGS: some implementations (including the original IBM PC) have a bug
>> which destroys BP
>
> That is on Trident cards, old card but may still be used, and BIOS may have
> been copied to other cards.
> Detected and documented on Gujin (boot.c and vgabios.h scroll)
Are you talking about BP or DS? As I said, the BP is well-known, and
the code accounts for it in the form of the INT10 macro.
>>>> and probably few other problems - just seen those by reading the patches (the
>>>> asm("") are inlined in the C code - I find it more difficult to check).
>>>>
>>>> Also, I do not know if "m" is right in here:
>>>> static inline u8 rdfs8(addr_t addr)
>>>> {
>>>> u8 v;
>>>> asm("movb %%fs:%1,%0" : "=r" (v) : "m" (*(u8 *)addr));
>>>> return v;
>>>> }
>> The "m" is correct right there.
>
> strange, "g" would mean anything can go there - and this assembly instruction
> should accept every access modes.
Not with an %fs: prefix. It would also allow the compiler to do a move
into a register "on its own", which would be disastrous, since it would
lack the prefix. So "m" is correct.
-hpa
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