linux-kernel - Re: [PATCH] libata: fix combined mode (was Re: Happy New Year (and v2.6.20-rc3 released))

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Message-ID: <459ACE9C.7020107@pobox.com>
Date:	Tue, 02 Jan 2007 16:29:00 -0500
From:	Jeff Garzik <jgarzik@...ox.com>
To:	Alan <alan@...rguk.ukuu.org.uk>
CC:	Linus Torvalds <torvalds@...l.org>,
	Alessandro Suardi <alessandro.suardi@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] libata: fix combined mode (was Re: Happy New Year (and
 v2.6.20-rc3 released))

Alan wrote:
>>> This is a silly complaint because the SFF layer in libata doesn't handle
>>> this case yet anyway.
>> Yes, it's "silly" people people use configurations you find inconvenient.
>>
>> At least one embedded x86 case cares, that I know of.  They only needed 
>> to make two minor changes to make it work.
> 
> *It is not part of 2.6.20*
> 
>> The code no long reserves resources for the "extra" PCI BAR that often 
>> exists on PCI controllers regardless of legacy/native mode.  Previously, 
>> the code called pci_request_regions() to reserve ALL regions attached to 
>> the PCI device.
> 
> We use BAR5 on two devices in legacy mode. Both of those reserve all the
> other resources.

Translation:  You want to hand-wave away an obvious regression that YOU 
have created with your fix-to-a-fix.

> We can fix BAR5 in .21 when all the combined mode crap
> goes away.

Translation:  Problems disappear in 2.6.21 because Jeff will revert the 
code I touched to its previous state -- always calling 
pci_request_regions() -- and all the problems I introduced by avoiding 
pci_request_regions() will go away.

Why INTRODUCE these 2.6.20 Alan-isms, if they are going away in 2.6.21?

>> You have suddenly decided that it's OK to --not reserve at all-- these 
>> additional regions.
> 
> It's not ideal - but it is perfectly sufficient for 2.6.20
> 
>> Proof:  The AHCI PCI BAR (#5, zero-based) is clearly NOT reserved, even 
>> though we talk to it, in piix_disable_ahci() of ata_piix.c.
> 
> We always claim the other BARs so catch a collision.

Where?  AFAICS, it is crystal clear the behavior:

* Prior to your patch, ata_piix in legacy mode calls 
pci_request_regions() to intentionally reserve ALL regions on the PCI 
device.

* After your patch, the code explicitly calls pci_request_region() for 
BARs 0-4, but never for BAR5.

Another driver is now free to claim a PCI BAR, and start running the 
hardware in AHCI mode, whee!

	Jeff

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