Subject: Re: Playing with SATA NCQ
From: Erik Slagter <erik@slagter.name>
To: Jeff Garzik <jgarzik@pobox.com>
Cc: linux-kernel@vger.kernel.org, linux-ide@vger.kernel.org,
       Jens Axboe <axboe@suse.de>
In-Reply-To: <20050529172949.GA3578@havoc.gtf.org>
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Date: Sun, 29 May 2005 19:45:03 +0200
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On Sun, 2005-05-29 at 13:29 -0400, Jeff Garzik wrote:
> On Sun, May 29, 2005 at 07:23:52PM +0200, Erik Slagter wrote:
> > On Sun, 2005-05-29 at 12:59 -0400, Jeff Garzik wrote:
> > > > My question was if there is a fundamental reason why the AHCI mode of
> > > > the ICH6/7 must be enabled by the BIOS, is there a reason why the kernel
> > > > doesn't do it, or can't do it?
> > > 
> > > The BIOS sets up PCI resources necessary to use AHCI mode.
> > 
> > Ok. So there's absolutely no way to do that afterwards? It'd really be a
> > pity :-(
> 
> It is technically possible.  BIOS is just software, just like the OS.
> 
> It's just a huge pain in the butt, because the kernel might accidentally
> stomp on some resources the BIOS secretly set up, or somesuch.

Ah, ok. I wasn't aware of this large role of the BIOS in setting up
hardware, nowadays. Grmbl.

> > On the same subject: is there a reason why ICH6 gets "BAR0-3 ignored"
> > and always gets the legacy i/o ports and IRQ's assigned? I'd say there
> > is absolutely no need to be compatible in this way, the PCI code can
> > assign the IRQ and I/O ports as with any other PCI device?
> 
> IDE is special.
> 
> This is due to how the BIOS sets up an IDE PCI device in legacy mode.
> BAR0-3 are set to zero, which is a signal to the OS that the IDE PCI
> device is in legacy mode (io 0x1f0+0x170, irq 14+15).  Since the IDE I/O
> ports are in ISA space not PCI space, the PCI BARs reflect nothing.

Goodie. So we will be stuck with MS/DOS compatibility until somewhere in
the next millenium.

I guess the only way to have, for example the ICH6, not using legacy
IRQ/ports, is to switch it to AHCI, which only the BIOS can do (if
implemented).

Thrilling.
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