linux-kernel - Re: [PATCH V3] VIA IRQ quirk behaviour change

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Message-ID: <450436F1.8070203@gentoo.org>
Date:	Sun, 10 Sep 2006 12:01:53 -0400
From:	Daniel Drake <dsd@...too.org>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
CC:	akpm@...l.org, torvalds@...l.org, sergio@...giomb.no-ip.org,
	jeff@...zik.org, greg@...ah.com, cw@...f.org, bjorn.helgaas@...com,
	linux-kernel@...r.kernel.org, harmon@....edu, len.brown@...el.com,
	vsu@...linux.ru, liste@...det.net
Subject: Re: [PATCH V3] VIA IRQ quirk behaviour change

Alan, sorry but I'm still having trouble understanding which aspect of 
my patch you are objecting to. I think I probably misinterpreted one of 
your earlier comments.

My patch included this comment:

> There is still a downside to this patch: if the user inserts a VIA
> PCI card into a VIA-based motherboard, in some circumstances the
> quirk will also run on
> the VIA PCI card. This corner case is hard to avoid.

To which you replied:

> NAK
> 
> This is not a "corner case"
> 
> Very large numbers of VIA mainboards ship with some of the VIA devices
> built in and some of them on the PCI bus. In fact they generally start
> shipped on the board as PCI devices and migrate over time.

and later followed up with:

> If they are on the V-Bus then the IRQ number controls routing if they
> are on the PCI bus the IRQ line controls routing as normal.

The scenario you are talking about there (internal devices on PCI bus vs 
V-bus) is different from the one I was talking about (external VIA-based 
PCI cards going into PCI slots on a VIA-based motherboard).

Regardless of that I tried to piece together what I thought you might be 
trying to say, in order to understand the NAK:

> OK, so per your last mail, most VIA devices start on the PCI bus and
> then later are migrated onto the V-bus.
> 
> Devices on the PCI bus need to be quirked (in some circumstances), as
> when they are on the PCI bus they use the IRQ line for routing, and
> the IRQ line is what the quirk actually modifies.
> 
> V-bus devices do not need the quirk because IRQ routing there is
> handled by IRQ number alone.
> 
> Is the above correct?

And then you replied:

> I've no idea. 

Can you clarify?

Thanks.
Daniel
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