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Re: [Qemu-devel] [PATCH 04/25] ahci: add ide device initialization helpe


From: Kevin Wolf
Subject: Re: [Qemu-devel] [PATCH 04/25] ahci: add ide device initialization helper
Date: Wed, 26 Sep 2012 12:43:48 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:13.0) Gecko/20120605 Thunderbird/13.0

Am 26.09.2012 10:15, schrieb Markus Armbruster:
> Jason Baron <address@hidden> writes:
>> I think that -drive if=ide should result in a disk attached piix3-ide.
>> Not in an ide disk attached to the ahci controller (which is current q35
>> bahavior, and is 'broken' b/c we don't want that to change after q35 is
>> introdued). The reason being is that I think there should be an easy way
>> to create an ide drive on piix3-ide, and an ide drive on the ahci
>> controller. But it sounds like you don't agree with this point.
> 
> Two issues with that:
> 
> 1. Why should q35 have a piix3-ide?  The ICH9 southbridge provides only
> SATA, so the board needs additional circuitry to provide PATA.  As far
> as I can tell, intel's Q35 doesn't.  ICH9-based boards that do certainly
> won't use a piix3-ide, because that's a *function* of the PIIX
> southbridge device.  It doesn't exist separately.
> 
> 2. Why should we connect -drive if=ide to a slow PATA controller instead
> of a perfectly servicable SATA controller?

Because the guest OS doesn't have an AHCI driver.

But I don't think that connecting to a slow PATA controller describes
exactly what we would ideally want to emulate. We'll probably want to
emulate a SATA controller that is in IDE emulation mode (or whatever it
is called). But as long as we don't have it, the PATA controller is
probably the right thing to provide.

>> But I'm not sure about using if=ide to use ich9-ahci. I'm suggesting
>> that if=ide should continue to refer to piix3-ide.
> 
> Perhaps it should mean "the board's preferred ATA controller", perhaps
> it should mean "the board's preferred PATA controller".  Certainly
> debatable.
> 
> If the latter, not necessarily piix3-ide.

I'd rephrase as "the board's preferred way to provide an IDE interface",
but yes, I think that's the real question.

If we ever want to make Q35 the default, if=ide must implement this
semantics. If we want to stay with PIIX forever, we have a choice. I'm
leaning towards implementing it anyway and just making if=ahci the
default for Q35 if no if is specified at all.

Kevin



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