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

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Message-ID: <Pine.LNX.4.64.0612131522310.5718@woody.osdl.org>
Date:	Wed, 13 Dec 2006 15:28:36 -0800 (PST)
From:	Linus Torvalds <torvalds@...l.org>
To:	Jan Engelhardt <jengelh@...ux01.gwdg.de>
cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	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 Wed, 13 Dec 2006, Jan Engelhardt wrote:
> 
> For the sharing case, some sort of softirq should be created. That is, when a
> hard interrupt is generated and the irq handler is executed, set a flag that at
> some other point in time, the irq is delivered to userspace. Like you do with
> signals in userspace:

NO.

The whole point is, YOU CANNOT DO THIS.

You need to shut the device up. Otherwise it keeps screaming.

Please, people, don't confuse the issue any further. A hardware driver

	ABSOLUTELY POSITIVELY HAS TO

have an in-kernel irq handler that knows how to turn the irq off.

End of story. No ifs, buts, maybes about it.

You cannot have a generic kernel driver that doesn't know about the 
low-level hardware (not with current hardware - you could make the "shut 
the f*ck up" a generic thing if you designed hardware properly, but that 
simply does not exist in general right now).

In short: a user-space device driver has exactly TWO choices:

 - don't use interrupts at all, just polling

 - have an in-kernel irq handler that at a minimum knows how to test 
   whether the irq came from that device and knows how to shut it up.

This means NOT A GENERIC DRIVER. That simply isn't an option on the 
table, no matter how much people would like it to be.

			Linus
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