Thank you for your reply. On Friday 16 November 2012 11:25:47 Len Brown wrote: > However, this patch can't possibly be the right way to go -- > as it is just as broken as the code it replaces. This is a well-aimed shot in the dark based on the DSDT I see. It is certainly not a solid proof that is won't break other machines and if it does break. As far as PCI is concerned, it only affects machines with multiple handles that have the same PCI address returned by _ADR. This method is also used by USB and others which I am more worried about (still, I think it will not happen, but hey, this is ACPI). Nowhere in the ACPI spec is stated what should happen with duplicate _ADR values for such devices. Maybe you can ask for a clarification on this at the ACPI team? (given that the ACPI spec is also worked on by Intel)? (the Windows Hardware Certification Requirements [1] is also not helpful on this topic) > Were I to bet, I'd say that it will break as many machines > as it fixes. And when it does, where are we? > > Clearly we need to be using a more clever search algorithm. Right, but what additional information can we throw at this in order to fix the linked bug? If you scan through it and wonder about the 0xFFFF value at _ADR, this is changed by PEGP._INI to 0. If this patch will not be included, I propose to print at least a debugging message when a duplicate handle is found (i.e. if find->handle != NULL). > thanks, > Len Brown, Intel Open Source Technology Center > > On 11/12/2012 05:28 PM, Lekensteyn wrote: > > From: Peter Wu <lekensteyn@xxxxxxxxx> > > > > When acpi_get_child is called, it loops through all direct child > > devices and calls do_acpi_find_child to find an ACPI handle matching the > > _ADR. The previous implementation visits every direct child, if there > > were multiple devices with a matching _ADR, the last match was always > > returned. > > > > This behaviour (returning the last result) does not work for many recent > > Lenovo machines when looking for the correct ACPI handle for a Nvidia > > PCI video device. On these machines, the first handle should be used > > instead of the last one. On these machines, the PCI Bus ID is 01:00.0, > > hence the address that is searched for is 0 (via acpi_pci_find_device). > > > > When acpi_pci_find_device calls acpi_get_child, it iterates through: > > Address: 00000000 (valid); handle: \_SB_.PCI0.PEG0.PEGP > > Address: 00000001 (valid); handle: \_SB_.PCI0.PEG0.VGA1 > > Address: 00000000 (valid); handle: \_SB_.PCI0.PEG0.VGA_ > > > > The correct handle here is "\_SB_.PCI0.PEG0.PEGP" which contains the > > _ROM method as well as _PSx for PM, and not \_SB.PCI0.PEG0.VGA. > > > > On my own laptop, and many others I believe, there is only one matching > > handle for a PCI device. The acpi_get_child method has been added in > > 2005, 4e10d12a3d88c88fba3258809aa42d14fd8cf1d1, and there is no message > > indicating that the last (or first) handle should be returned. However, > > it is kind of useless to iterate from beginning to the end if you only > > need the last match. Therefore, just return the first match (which is > > likely the last one too in almost all cases). > > > > Verified to work for an affected Lenovo Ideapad Y480, tested for no > > regressions on my laptop (Clevo B7130). > > > > Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=42696 > > > > Tested-by: Sergio Perez <dagobertstaler@xxxxxxxxx> > > Signed-off-by: Peter Wu <lekensteyn@xxxxxxxxx> > > --- > > > > drivers/acpi/glue.c | 8 +++++--- > > 1 file changed, 5 insertions(+), 3 deletions(-) > > > > diff --git a/drivers/acpi/glue.c b/drivers/acpi/glue.c > > index 0837308..dc9c945 100644 > > --- a/drivers/acpi/glue.c > > +++ b/drivers/acpi/glue.c > > @@ -99,18 +99,20 @@ struct acpi_find_child { > > > > static acpi_status > > do_acpi_find_child(acpi_handle handle, u32 lvl, void *context, void **rv) > > { > > > > - acpi_status status; > > + acpi_status status, ret = AE_OK; > > > > struct acpi_device_info *info; > > struct acpi_find_child *find = context; > > > > status = acpi_get_object_info(handle, &info); > > if (ACPI_SUCCESS(status)) { > > > > if ((info->address == find->address) > > > > - && (info->valid & ACPI_VALID_ADR)) > > + && (info->valid & ACPI_VALID_ADR)) { > > > > find->handle = handle; > > > > + ret = AE_CTRL_TERMINATE; > > + } > > > > kfree(info); > > > > } > > > > - return AE_OK; > > + return ret; > > > > } > > > > acpi_handle acpi_get_child(acpi_handle parent, u64 address) [1]: http://msdn.microsoft.com/en-US/library/windows/hardware/jj128256 -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
