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From: Linus Torvalds on 14 May 2010 11:00 On Fri, 14 May 2010, Eric W. Biederman wrote: > > efi_enabled is a guard on efi calls. If it is true it tells you that > you can make runtime efi calls. If it is false you can't use runtime > efi calls. efi_enabled does not tell you about the presence of efi > on a system. We don't really want to know about the "presense". What we want to know about is whether we were _loaded_ with EFI or not. IOW, even if the system is EFI-capable, if we actually booted through the legacy BIOS interfaces, we would consider ourselves in "legacy" mode. > All of which means in the normal case pay attention to acpi. That is > more likely to be correct and usable than EFI anything. Oh yes. ACPI is actually _tested_, so while it's buggy, it's unlikely to be quite as spectacularly buggy as any EFI interfaces probably are. But the issue here is that on a "legacy PC", we can't just say "ACPI doesn't mention this device, so it can't exist". Because in a legacy PC model, that simply isn't true. All those motherboard devices can easily exist (and do!) even if ACPI/PnP don't mention them. But if we live in a non-legacy world (ie we were loaded through EFI), I think it's much more reasonable to say "we'll ignore any devices not mentioned by ACPI". Linus -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Linus Torvalds on 14 May 2010 11:20 On Fri, 14 May 2010, Matthew Garrett wrote: > > I've done some experimentation under qemu. On ACPI systems, Windows will > *only* touch the keyboard controller if there's a device with an > appropriate PNP HID or CID and if _STA evaluates to 0x0b or 0x0f. > Otherwise it'll simply ignore the hardware entirely. By the looks of it > their keyboard probing is also somewhat different to ours, but that's > probably another story. Well, I'd hate to lose the keyboard hotplug capability, but at the same time, it _is_ 2010, and while I have personally used it historically, I don't really foresee ever using it again. So we _could_ decide to just try it, and see if anybody screams. If nobody does, that would be a very simple solution to the problem. Linus -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Matthew Garrett on 14 May 2010 11:40 On Fri, May 14, 2010 at 07:54:53AM -0700, Linus Torvalds wrote: > But the issue here is that on a "legacy PC", we can't just say "ACPI > doesn't mention this device, so it can't exist". Because in a legacy PC > model, that simply isn't true. All those motherboard devices can easily > exist (and do!) even if ACPI/PnP don't mention them. I think that's true except in the case where the Leading Other OS won't use a device unless it's present in ACPI - that kind of enforcement tends to concentrate vendors' minds, even if they'd otherwise be busy filling data tables with garbage. -- Matthew Garrett | mjg59(a)srcf.ucam.org -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Linus Torvalds on 14 May 2010 11:50 On Fri, 14 May 2010, Matthew Garrett wrote: > > I think that's true except in the case where the Leading Other OS won't > use a device unless it's present in ACPI - that kind of enforcement > tends to concentrate vendors' minds, even if they'd otherwise be busy > filling data tables with garbage. Largely true. That said, nobody uses Windows in a headless environment, the way people _do_ use Linux and then later plug in a keyboard. Also, even with Windows, I do wonder if they have things like cut-off dates for trusting ACPI. We certainly do. Linus -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Matthew Garrett on 14 May 2010 11:50
On Fri, May 14, 2010 at 08:42:59AM -0700, Linus Torvalds wrote: > Also, even with Windows, I do wonder if they have things like cut-off > dates for trusting ACPI. We certainly do. Yeah, I think they cut off around 2000 or so. I should try feeding it different DMI strings to see what happens. -- Matthew Garrett | mjg59(a)srcf.ucam.org -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |