linux-kernel - Re: [PATCH] i2c-scmi: Quirk to work on IBM machines with broken BIOSes

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Date:	Wed, 21 Oct 2009 10:37:33 -0700
From:	"Darrick J. Wong" <djwong@...ibm.com>
To:	Bjorn Helgaas <bjorn.helgaas@...com>
Cc:	Crane Cai <crane.cai@....com>, lenb@...nel.org,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-i2c@...r.kernel.org, linux-acpi@...r.kernel.org
Subject: Re: [PATCH] i2c-scmi: Quirk to work on IBM machines with broken
	BIOSes

On Wed, Oct 21, 2009 at 08:57:13AM -0600, Bjorn Helgaas wrote:
> On Tuesday 20 October 2009 08:30:16 pm Crane Cai wrote:
> > Hi Darrick,
> > 
> > On Tue, Oct 20, 2009 at 04:11:49PM -0700, Darrick J. Wong wrote:
> > > On some old IBM workstations and desktop computers, the BIOS presents in
> > > the DSDT an SMBus object that is missing the HID identifier that the
> > > i2c-scmi driver looks for.  It also omits the leading "_" in the method
> > > names (it should be _SBR, not SBR_).  Modify the ACPI device scan code to
> > > insert the missing HID if it finds an IBM system with such an object, and
> > > modify the i2c-scmi driver to handle the odd method names.
> > I have a suggestion: You can need not to add quirk in acpi part, instead
> > you can add your ACPI device HID in i2c-scmi with your specificied methods
> > set.

The problem is that the BIOS does not provide an HID for the SMBus object at
all...

> Maybe Darrick understands your suggestion, but I don't.  The only way
> i2c-scmi ever learns about a device is when acpi_smbus_cmi_add() is
> called, and that's only called when the Linux/ACPI core has found a
> device that matches "SMBUS01".
> 
> Can you elaborate on your suggestion?
> 
> The i2c-scmi driver *could* walk the whole namespace itself, looking
> for devices with the SBI/SBR/SBW methods, but I like Darrick's quirk
> approach better because it allows i2c-scmi to continue to use the
> normal ACPI driver model.

...which is why I need the quirk to stuff one in at the OS level.  Were it as
simple as recognizing a different HID, I could have written a less intrusive
patch. :/

--D
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