According to the ACPI 6.4 spec:
It is strongly recommended that the OS evaluate _OSC with the Query
Support Flag set until _OSC returns the Capabilities Masked bit clear,
to negotiate the set of features to be granted to the OS for native
support; a platform may require a specific combination of features
to be supported natively by an OS before granting native control
of a given feature. After negotiation with the query flag set,
the OS should evaluate without it so that any negotiated values
can be made effective to hardware.
Currently the code sends the exact same values in both executions of the
_OSC and this leads to some problems on some AMD platforms in certain
configurations.
The following notable capabilities are set by OSPM when query is enabled:
* OSC_SB_PR3_SUPPORT
* OSC_SB_PCLPI_SUPPORT
* OSC_SB_NATIVE_USB4_SUPPORT
The first call to the platform OSC returns back a masked capabilities
error because the firmware did not acknowledge OSC_SB_PCLPI_SUPPORT but
it acknolwedged the others.
The second call to the platform _OSC without the query flag set then
fails because the OSPM still sent the exact same values. This leads
to not acknowledging OSC_SB_NATIVE_USB4_SUPPORT and later USB4 PCIe
tunnels can't be authorized.
This problem was first introduced by commit 159d8c274fd9 ("ACPI: Pass the
same capabilities to the _OSC regardless of the query flag") which subtly
adjusted the behavior from 719e1f5 ("ACPI: Execute platform _OSC also
with query bit clear").
The _OSC was called exactly 2 times:
* Once to query and request from firmware
* Once to commit to firmware without query
To fix this problem, continue to call the _OSC until the firmware has
indicated that capabilities are no longer masked or after an arbitrary
number of negotiation attempts.
Furthermore, to avoid the problem that commit 159d8c274fd9 ("ACPI: Pass
the same capabilities to the _OSC regardless of the query flag")
introduced, explicitly mark support for CPC and CPPCv2 even if they
were masked by the series of query calls due to table loading order on
some systems.
Fixes: 159d8c274fd9 ("ACPI: Pass the same capabilities to the _OSC regardless of the query flag")
Signed-off-by: Mario Limonciello <mario.limonciello@xxxxxxx>
---
This series was accepted but showed a regression in another use of acpi_run_osc
so the series was dropped.
Changes from v4->v5:
* Move negotiation entirely into acpi_bus_osc_negotiate_platform_control
drivers/acpi/bus.c | 31 ++++++++++++++++++++++++++++---
1 file changed, 28 insertions(+), 3 deletions(-)
diff --git a/drivers/acpi/bus.c b/drivers/acpi/bus.c
index b96c54813886..86d88bd72c07 100644
--- a/drivers/acpi/bus.c
+++ b/drivers/acpi/bus.c
@@ -294,6 +294,7 @@ static void acpi_bus_osc_negotiate_platform_control(void)
.cap.pointer = capbuf,
};
acpi_handle handle;
+ int i;
capbuf[OSC_QUERY_DWORD] = OSC_QUERY_ENABLE;
capbuf[OSC_SUPPORT_DWORD] = OSC_SB_PR3_SUPPORT; /* _PR3 is in use */
@@ -329,10 +330,34 @@ static void acpi_bus_osc_negotiate_platform_control(void)
if (ACPI_FAILURE(acpi_get_handle(NULL, "\\_SB", &handle)))
return;
- if (ACPI_FAILURE(acpi_run_osc(handle, &context)))
- return;
+ /*
+ * Check if bits were masked, we need to negotiate
+ * prevent potential endless loop by limited number of
+ * negotiation cycles.
+ */
+ for (i = 0; i < 5; i++) {
+ bool retry = false;
+
+ if (ACPI_FAILURE(acpi_run_osc(handle, &context)))
+ return;
+ capbuf_ret = context.ret.pointer;
+ retry = capbuf_ret[OSC_SUPPORT_DWORD] != capbuf[OSC_SUPPORT_DWORD];
+ capbuf[OSC_SUPPORT_DWORD] = capbuf_ret[OSC_SUPPORT_DWORD];
+ kfree(context.ret.pointer);
+ if (!retry)
+ break;
+ }
- kfree(context.ret.pointer);
+ /*
+ * Avoid problems with BIOS dynamically loading tables by indicating
+ * support for CPPC even if it was masked.
+ */
+#ifdef CONFIG_X86
+ if (boot_cpu_has(X86_FEATURE_HWP)) {
+ capbuf[OSC_SUPPORT_DWORD] |= OSC_SB_CPC_SUPPORT;
+ capbuf[OSC_SUPPORT_DWORD] |= OSC_SB_CPCV2_SUPPORT;
+ }
+#endif
/* Now run _OSC again with query flag clear */
capbuf[OSC_QUERY_DWORD] = 0;
--
2.34.1
