From: "Giampaolo Tomassoni" <g.tomassoni@libero.it>
To: "Robert Hancock" <hancockr@shaw.ca>
Cc: "Linux Kernel ML" <linux-kernel@vger.kernel.org>
Subject: R: R: How to avoid serial port buffer overruns?
Date: Fri, 18 Aug 2006 16:58:07 +0200
Message-ID: <NBBBIHMOBLOHKCGIMJMDIEKFFNAA.g.tomassoni@libero.it>
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> -----Messaggio originale-----
> Da: Robert Hancock [mailto:hancockr@shaw.ca]
> Inviato: venerd? 18 agosto 2006 16.31
> A: Giampaolo Tomassoni
> Cc: Linux Kernel ML
> Oggetto: Re: R: How to avoid serial port buffer overruns?
>
> IRQ_HANDLED vs. IRQ_NONE has no effect on what interrupt handlers are 
> called, etc. It is only used to detect if an interrupt is firing without 
> being handled by any driver, in this case the kernel can detect this and 
> disable the interrupt.
> 
> I'm not sure exactly why the driver is returning IRQ_HANDLED all the 
> time, but edge-triggered interrupts are always tricky and there may be a 
> case where it can't reliably detect this. Returning IRQ_HANDLED is the 
> safe thing to do if you cannot be sure if your device raised an 
> interrupt or not.

Oh, I see. This in handle_IRQ_event in /kernel/irq/handle.c confirms what you said:

        do {
                ret = action->handler(irq, action->dev_id, regs);
                if (ret == IRQ_HANDLED)
                        status |= action->flags;
                retval |= ret;
                action = action->next;
        } while (action);

There is no escape from the loop when the handler returns IRQ_HANDLED.

Thanks,

	giampaolo

> 
> -- 
> Robert Hancock      Saskatoon, SK, Canada
> To email, remove "nospam" from hancockr@nospamshaw.ca
> Home Page: http://www.roberthancock.com/
> 

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