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SubjectRe: Lenovo ThinkPads need acpi_osi="Linux"
On Sat 2008-01-12 04:16:08, Len Brown wrote:
> On Friday 11 January 2008 21:23, Henrique de Moraes Holschuh wrote:
> > While helping a user find out what happened to his mute key, I found out
> > that the Lenovo BIOSes need the OSI string Linux defined to behave properly
> > in Linux.
> >
> > Lenovo has been attempting to make things a bit easier for Linux on their
> > ThinkPads, by disabling the more obnoxious behaviours of the firmware (used
> > by their Windows drivers) when in Linux. It looks like they used the OSI
> > string for that.
> >
> > It is probably worthwhile to give a head's up: regressions involving
> > thinkpads and 2.6.23+ should probably have a 'please test with
> > acpi_osi="Linux"' step added if there is any chance ACPI AML code, BIOS or
> > SMBIOS code, or EC behaviour could be involved.
> >
> > The most concrete example I have right now of changed behaviour is the Mute
> > key on the T61, which just plain disappears if acpi_osi="!Linux" (2.6.23
> > default).
> >
> > I have also seen some hacked DSDTs around (mostly for older T4x models)
> > which used the Linux OSI string to fix or work around AML weirdness. Those
> > would break in 2.6.23 (and 2.6.24?) as well.
> >
> > Now, what should we do about it? Add a quirk to always define the Linux OSI
> > string on ThinkPads (based on DMI information)? All IBM ones (which won't
> > have BIOS revisions anymore, anyway) deal well with it, and Lenovo ones
> > seem to benefit from it.
> >
> > We could also ask Lenovo to change the BIOS to stop paying attention to that
> > OSI string, but they will likely want/need a trigger for the AML code to
> > know it should change behaviour anyway, and the OSI string *does* look like
> > the proper thing to use IMHO. I don't know if we could get them to arrive
> > to a behaviour that is acceptable both to us, and also to their Windows
> > drivers...
> >
> I discussed this with Lenovo a few months ago
> and made it clear that Linux will unlikely
> default to answer yes to OSI(Linux) in the future --
> for all the reasons I stated when I disabled it.
> However, they told me they wanted to use OSI(Linux)
> to enable the backlight (via video re-post) on S3 resume,
> and the problem at hand was a distro kernel which still
> had OSI(Linux), so that is what they did.
> I was unaware that they're using it for anything else,
> and the fact that they are lends further support to
> the case that as an OS interface string "Linux"
> is too vague to be meaningful.
> They seemed open to looking for another string, say
> "Needs S3 video re-post". However, we didn't
> agree on such a string, and so it isn't in Linux
> or the Lenovo BIOS.
> I think until we have native Linux graphics driver for (fast)
> backlight restore, we need to add a DMI to enable OSI(Linux)
> for the offending Lenovo models. We'll need to have
> some coordination with the graphics guys so that they
> can turn this off from user-space when they don't need it.
> The reason it shoudl be turned off is that backlight enabling
> backlight from a native graphics driver is much faster than running
> through the video BIOS POST. So if we keep the OSI(Linux)
> video BIOS POST workaround in place permanently, it would
> put Linux at a permanent performance disadvantage to Windows.

Hmm, they should not need to do anything.

When linux calls video BIOS with lcall (acpi_sleep=s3_bios), they
should turn on backlight and put video into text mode. They should
also make sure mode setting works after that.

I don't see how ACPI fits into this picture, and I think it can work
well without ACPI tricks.

(cesky, pictures)

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