Quick aic7xxx bug hunt...

[Jeff Garzik <jgarzik@mandrakesoft.com>]

Justin T. Gibbs wrote:
> On some motherboards with some chipsets, you can get these messages if
> another busmaster (say an IDE drive or a sound card) is hogging the bus.
> Usually this is with a VIA chipset.  Its not clear why the aic7xxx_old
> driver would behave differently other than it disables memory write
> and invalidate PCI transactions on this chip.  The new driver doesn't
> need that work around.


Justin,

One thing I notice is at least one PCI posting bug.  When using MMIO 
(write[bwlq] under Linux), you _must_ use a read[bwlq] to flush the 
write to PCI, if you wish to ensure the write posts at a certain point 
in the code.

Here is the example PCI posting bug, in ahc_clear_critical_section:
>                 ahc_outb(ahc, HCNTRL, ahc->unpause);
>                 do {
>                         ahc_delay(200);
>                 } while (!ahc_is_paused(ahc));

As you can see, there is no read before the udelay(), which is very 
wrong on modern CPUs with write posting...  that's definitely a driver 
bug that will bite you on modern x86 motherboards [and is totally broken 
on ia64 and other platforms].

Please let me know if you have further questions on PCI write posting...

	Jeff