On Thu, Feb 24, 2022 at 11:52:24PM -0600, Mario Limonciello wrote: > 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 _OSC > 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 acknolwedge OSC_SB_PCLPI_SUPPORT but acknowledge > it acknolwedged the others. > > The second call to the platform OSC without the query flag set then _OSC > 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 _OSC > 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> > --- > changes from v1->v2: > * Fix a NULL pointer dereference caught by 0day CI > drivers/acpi/bus.c | 30 ++++++++++++++++++++++++++++-- > 1 file changed, 28 insertions(+), 2 deletions(-) > > diff --git a/drivers/acpi/bus.c b/drivers/acpi/bus.c > index f0f9e0934c10..489cc4f6b6e6 100644 > --- a/drivers/acpi/bus.c > +++ b/drivers/acpi/bus.c > @@ -297,6 +297,8 @@ static void acpi_bus_osc_negotiate_platform_control(void) > .cap.pointer = capbuf, > }; > acpi_handle handle; > + acpi_status status; > + int i; > > capbuf[OSC_QUERY_DWORD] = OSC_QUERY_ENABLE; > capbuf[OSC_SUPPORT_DWORD] = OSC_SB_PR3_SUPPORT; /* _PR3 is in use */ > @@ -332,10 +334,34 @@ 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))) > + /* > + * check if bits were masked, we need to negotiate > + * prevent potential endless loop by limited number of > + * negotiation cycles Start with capital letter and end with '.' a multiline comment. /* * Check if ... * ... * negotiation cycles. */ > + */ > + for (i = 0; i < 5; i++) { > + status = acpi_run_osc(handle, &context); > + if (ACPI_SUCCESS(status) || status == AE_SUPPORT) { > + capbuf_ret = context.ret.pointer; > + capbuf[OSC_SUPPORT_DWORD] = capbuf_ret[OSC_SUPPORT_DWORD]; > + kfree(context.ret.pointer); I wonder if it makes sense to document the acpi_run_osc() to tell in which return codes you actually need to kfree() the result. Here it is hard to tell IMHO. > + } > + if (status != AE_SUPPORT) > + break; > + } > + if (ACPI_FAILURE(status)) > return; > > - kfree(context.ret.pointer); > + /* > + * avoid problems with BIOS dynamically loading tables by indicating > + * support for CPPC even if it was masked Ditto for the comment. > + */ > +#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