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

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Date:	Wed, 13 Dec 2006 23:30:55 +0100
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	Linus Torvalds <torvalds@...l.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 Thu, 2006-12-14 at 09:14 +1100, Benjamin Herrenschmidt wrote:
> the edge flow is easy. the level one is:
> 
>  - IRQ happens
>  - kernel handler masks it and queue a msg for userland
>  - later on, userland gets the message, talks to the device,
>    (MMAP'ed mmio, acks the interrupt on the device itself) and
>    does an ioctl/syscall/write/whatever to tell kernel it's done
>  - kernel unmasks it.

That's simply not true.

- IRQ happens
- kernel handler runs and masks the chip irq, which removes the IRQ
request
- user space message get queued or waiting reader woken
- kernel handler returns IRQ_HANDLED, which reenables the irq in the PIC
- user space handles the device
- user space reenables the device irq

No need for an ioctl. Neither for edge nor for level irqs.

	tglx


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