Date: Fri, 24 Sep 2004 14:52:29 +0900 (JST)
Message-Id: <20040924.145229.108814142.t-kochi@bq.jp.nec.com>
To: kaneshige.kenji@jp.fujitsu.com
Cc: bjorn.helgaas@hp.com, acpi-devel@lists.sourceforge.net,
       kaneshige.kenji@soft.fujitsu.com, akpm@osdl.org, greg@kroah.com,
       len.brown@intel.com, tony.luck@intel.com, linux-kernel@vger.kernel.org,
       linux-ia64@vger.kernel.org
Subject: Re: [ACPI] [PATCH] PCI IRQ resource deallocation support [2/3]
From: Takayoshi Kochi <t-kochi@bq.jp.nec.com>
In-Reply-To: <4150D458.3050400@jp.fujitsu.com>
References: <414FEBDB.2050201@soft.fujitsu.com>
	<200409210857.59457.bjorn.helgaas@hp.com>
	<4150D458.3050400@jp.fujitsu.com>
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From: Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>
Subject: Re: [ACPI] [PATCH] PCI IRQ resource deallocation support [2/3]
Date: Wed, 22 Sep 2004 10:24:40 +0900

> >> +  * dev->irq is cleared by BIOS-assigned IRQ set during boot.
> >> +  */
> >> + pci_read_config_byte(dev, PCI_INTERRUPT_PIN, &irq);
> >> + if (irq)
> >> +  pci_read_config_byte(dev, PCI_INTERRUPT_LINE, &irq);
> >> + dev->irq = irq;
> > 
> > Why do we need to fiddle with dev->irq?  I think it should
> > just be undefined after acpi_pci_irq_disable().
> 
> I had been considering what the "undefined dev->irq" was.
> In fact, I had other ideas that was clearing it by zero or
> -1 (0xffffffff). But I didn't know if we can use these values
> as a undefined IRQ number. So I'm clearing it by the value
> which was assigned by PCI core code (pci_read_irq()) before
> acpi_pci_irq_enable() was called. 

I think it has little sense in restoring value from the configuration
space to dev->irq or clearing it.

If we do preventive programming, it may be worth
trying to define some magic constant (e.g. PCI_UNDEFINED_IRQ) and
panic/BUG when the irq is being enabled.
Otherwise, leaving dev->irq as it is would be ok.

---
Takayoshi Kochi <t-kochi@bq.jp.nec.com>
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