[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

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


  • To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • From: Alan Cox <alan@xxxxxxxxxxxxxxxxxxx>
  • Date: Tue, 27 Nov 2012 17:49:00 +0000
  • Cc: "Keir \(Xen.org\)" <keir@xxxxxxx>, "Tim \(Xen.org\)" <tim@xxxxxxx>, "xen-devel@xxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxx>
  • Delivery-date: Tue, 27 Nov 2012 17:44:03 +0000
  • Face: 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
  • List-id: Xen developer discussion <xen-devel.lists.xen.org>

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

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel


 


Rackspace

Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.