Re: [PATCH v5] ACPI: bus: For platform OSC negotiate capabilities

[Mika Westerberg <mika.westerberg@linux.intel.com>]

On Wed, Mar 09, 2022 at 10:37:49AM -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
> 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@amd.com>
> ---
> 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

Probably worth mentioning that the v5 fixes memory leak that was
reported.

Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>