linux-kernel - Re: [GIT PATCH] more Driver core patches for 2.6.19

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Date:	Wed, 13 Dec 2006 13:26:33 -0800 (PST)
From:	Linus Torvalds <torvalds@...l.org>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
cc:	Greg KH <gregkh@...e.de>, Andrew Morton <akpm@...l.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [GIT PATCH] more Driver core patches for 2.6.19

On Thu, 14 Dec 2006, Benjamin Herrenschmidt wrote:
>
> Actually, you can... but wether you want is a different story :-)
> 
> You can simply mask it, have it handled by userspace and re-enable it
> when that's done.

Nope. Again, this whole mentality is WRONG.

It DOES NOT WORK. No architecture does per-device interrupts portably, 
which means that you'll always see sharing. 

And once you see sharing, you have small "details" like the harddisk 
interrupt or network interrupt that the user-land driver will depend on.

Oops. Instant deadlock.

> I don't mean I -like- the approach... I just say it can be made to
> sort-of work. But I don't see the point.

No. The point really is that it fundamentally _cannot_ work. Not in the 
real world.

It can only work in some alternate reality where you can always disable 
interrupts per-device, and even in that alternate reality it would be 
wrong to use that quoted interrupt handler: not only do you need to 
disable the irq, you need to have an "acknowledge" phase too

So you'd actually have to fix things _architecturally_, not just add some 
code to the irq handler.

		Linus
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