Re: [PATCH 0/4] PCI legacy I/O port free driver (take4)

From: Jeff Garzik <jgarzik@pobox.com>
To: Russell King <rmk+lkml@arm.linux.org.uk>
Cc: Grant Grundler <grundler@parisc-linux.org>,
	Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>,
	Andrew Morton <akpm@osdl.org>, Greg KH <greg@kroah.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	linux-pci@atrey.karlin.mff.cuni.cz
Subject: Re: [PATCH 0/4] PCI legacy I/O port free driver (take4)
Date: Thu, 02 Mar 2006 13:12:35 -0500	[thread overview]
Message-ID: <44073593.60703@pobox.com> (raw)
In-Reply-To: <20060302180025.GC28895@flint.arm.linux.org.uk>

Russell King wrote:
> It's not really "I/O port resource allocation" though - the resources
> have already been allocated and potentially programmed into the BARs
> well before the driver gets anywhere near the device.
[...]
> Are you implying that somehow resources are allocated at pci_enable_device
> time?  If so, shouldn't we be thinking of moving completely to that model
> rather than having yet-another-pci-setup-model.

Actually, that's has been the rule ever since the cardbus days: 
resources -- bars and irqs -- should not be considered allocated until 
after pci_enable_device().

Documentation/pci.txt reflects this reality as well:

> 3. Enabling and disabling devices
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>    Before you do anything with the device you've found, you need to enable
> it by calling pci_enable_device() which enables I/O and memory regions of
> the device, allocates an IRQ if necessary, assigns missing resources if
> needed and wakes up the device if it was in suspended state. Please note
> that this function can fail.

Any PCI driver that presumes -anything- about resources before calling 
pci_enable_device() is buggy, and that's been the case for many years. 
Some platform-specific PCI drivers violate this with special knowledge, 
but overall that's the rule.

Regards,

	Jeff