Re: [Xen-devel] [PATCH 2 of 5] rombios/ata: Do not wait for BSY to be set

[Alan Cox <alan@xxxxxxxxxxxxxxxxxxx>]

O> SEABios has explicitly removed the wait for the BSY bit to be set.  We
> want to remove it because Qemu will not set the BSY bit, resulting in

So why not fix the qemu emulation bug ?

> 42k needless polled IO traps while we wait for the timeout (which is, if
> I remember correctly, based on a loop counter rather than any notion of
> actual time)

Not good, although half caused by the fact that years on qemu still
hasn't implemented predictors to avoid trapping further than the kernel
layer 8)

> We can certainly argue about the outb(0x80,0x00).  When I was comparing
> ROMBios with SEABios, this outb was the closest I could easily get to a
> udelay(5) without implement udelay() in ROMBios.  Xen will execute an
> outb(0x80, 0x00) on the real hardware if a guest executes it; 

Don't do that then. 0x80 is not safe on a modern PC system (you'll note
the Linux kernel changed behaviour here). It may be a debug port but we've
seen some hardware do worse things if you touch it. It's also completely
out on a limb with EFI based systems which don't necessarily have the
legacy stuff present.

Alan

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