linux-kernel - Re: devres and requesting resources

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Message-ID: <20080229135556.6eafe4aa@core>
Date:	Fri, 29 Feb 2008 13:55:56 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Jeff Garzik <jeff@...zik.org>
Cc:	Tejun Heo <htejun@...il.com>,
	Linux IDE mailing list <linux-ide@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: devres and requesting resources

> Only rare PCI devices are shareable among multiple drivers.

Really. Let me see
	AGP & EDAC
	Serial/Parallel combo ports
	MPIIX
	CS5520
	Lots of I2C bus stuff
	VGA v 3D

There are quite a few, and some are already quite fun enough with our pci
struct model.

> sata_* at least intentionally used pci_request_regions() because it is 
> obvious from the hardware spec that multiple regions accessed by 
> multiple drivers is highly unlikely, without the driver being 
> specifically coded to support such sharing.  Such sharing code is far 
> beyond simple resource reservation, to avoid stepping on toes when there 
> is a single MMIO region and set of interrupt clearing registers.
> 
> So reading your email it sounds like there are valid cases for both 
> configurations.
> 
> Its a design choice either way, not a bug either way.

It is a flaw: devres that assumes it should grab all resources is unusable
for some other drivers - it is no longer generic and that makes it far
less useful. I've got no problem with the idea of a devres way to say
"and I want it all, mine mine mine" but that should not be the only
behaviour.

Alan
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