On Saturday, August 21, 2010, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rjw@xxxxxxx>
>
> There is the assumption in acpi_pci_osc_control_set() that it is
> always sufficient to compare the mask of _OSC control bits to be
> requested with the result of an _OSC query where all of the known
> control bits have been checked. However, in general, that need not
> be the case. For example, if an _OSC feature A depends on an _OSC
> feature B and control of A, B plus another _OSC feature C is
> requested simultaneously, the BIOS may return A, B, C, while it would
> only return C if A and C were requested without B.
>
> That may result in passing a wrong mask of _OSC control bits to an
> _OSC control request, in which case the BIOS may only grant control
> of a subset of the requested features. Moreover, acpi_pci_run_osc()
> will return error code if that happens and the caller of
> acpi_pci_osc_control_set() will not know that it's been granted
> control of some _OSC features. Consequently, the system will
> generally not work as expected.
>
> For this reason, make acpi_pci_osc_control_set() always check if
> control of the requested _OSC features will be granted before making
> the final control request. As a result, the osc_control_qry and
> osc_queried members of struct acpi_pci_root are not necessary any
> more, so drop them and remove the remaining code referring to them.
>
> Signed-off-by: Rafael J. Wysocki <rjw@xxxxxxx>
I have a new version of the changelog due to a discovery I made while testing
the patchset, but the patch is not too big, so appended is the entire thing.
Thanks,
Rafael
---
From: Rafael J. Wysocki <rjw@xxxxxxx>
Subject: ACPI / PCI: Do not preserve _OSC control bits returned by a query (v4)
There is the assumption in acpi_pci_osc_control_set() that it is
always sufficient to compare the mask of _OSC control bits to be
requested with the result of an _OSC query where all of the known
control bits have been checked. However, in general, that need not
be the case. For example, if an _OSC feature A depends on an _OSC
feature B and control of A, B plus another _OSC feature C is
requested simultaneously, the BIOS may return A, B, C, while it would
only return C if A and C were requested without B.
That may result in passing a wrong mask of _OSC control bits to an
_OSC control request, in which case the BIOS may only grant control
of a subset of the requested features. Moreover, acpi_pci_run_osc()
will return error code if that happens and the caller of
acpi_pci_osc_control_set() will not know that it's been granted
control of some _OSC features. Consequently, the system will
generally not work as expected.
Apart from this acpi_pci_osc_control_set() always uses the mask
of _OSC control bits returned by the very first invocation of
acpi_pci_query_osc(), but that is done with the second argument
equal to OSC_PCI_SEGMENT_GROUPS_SUPPORT which generally happens
to affect the returned _OSC control bits.
For these reasons, make acpi_pci_osc_control_set() always check if
control of the requested _OSC features will be granted before making
the final control request. As a result, the osc_control_qry and
osc_queried members of struct acpi_pci_root are not necessary any
more, so drop them and remove the remaining code referring to them.
Signed-off-by: Rafael J. Wysocki <rjw@xxxxxxx>
---
drivers/acpi/pci_root.c | 20 +++++++-------------
include/acpi/acpi_bus.h | 3 ---
2 files changed, 7 insertions(+), 16 deletions(-)
Index: linux-2.6/drivers/acpi/pci_root.c
===================================================================
--- linux-2.6.orig/drivers/acpi/pci_root.c
+++ linux-2.6/drivers/acpi/pci_root.c
@@ -249,12 +249,8 @@ static acpi_status acpi_pci_query_osc(st
status = acpi_pci_run_osc(root->device->handle, capbuf, &result);
if (ACPI_SUCCESS(status)) {
root->osc_support_set = support;
- if (control) {
+ if (control)
*control = result;
- } else {
- root->osc_control_qry = result;
- root->osc_queried = 1;
- }
}
return status;
}
@@ -409,14 +405,12 @@ acpi_status acpi_pci_osc_control_set(acp
goto out;
/* Need to query controls first before requesting them */
- if (!root->osc_queried) {
- status = acpi_pci_query_osc(root, root->osc_support_set, NULL);
- if (ACPI_FAILURE(status))
- goto out;
- }
- if ((root->osc_control_qry & control_req) != control_req) {
- printk(KERN_DEBUG
- "Firmware did not grant requested _OSC control\n");
+ flags = control_req;
+ status = acpi_pci_query_osc(root, root->osc_support_set, &flags);
+ if (ACPI_FAILURE(status))
+ goto out;
+
+ if (flags != control_req) {
status = AE_SUPPORT;
goto out;
}
Index: linux-2.6/include/acpi/acpi_bus.h
===================================================================
--- linux-2.6.orig/include/acpi/acpi_bus.h
+++ linux-2.6/include/acpi/acpi_bus.h
@@ -377,9 +377,6 @@ struct acpi_pci_root {
u32 osc_support_set; /* _OSC state of support bits */
u32 osc_control_set; /* _OSC state of control bits */
- u32 osc_control_qry; /* the latest _OSC query result */
-
- u32 osc_queried:1; /* has _OSC control been queried? */
};
/* helper */
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