linux-kernel - Re: [PATCH v3 1/2] ACPI: CPPC: Only probe for

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Date:   Fri, 1 Jul 2022 08:48:40 +0300
From:   Mika Westerberg <mika.westerberg@...ux.intel.com>
To:     Mario Limonciello <mario.limonciello@....com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Len Brown <lenb@...nel.org>, Huang Rui <ray.huang@....com>,
        perry.yuan@....com, CUI Hao <cuihao.leo@...il.com>,
        maxim.novozhilov@...il.com, lethe.tree@...tonmail.com,
        garystephenwright@...il.com, galaxyking0419@...il.com,
        linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/2] ACPI: CPPC: Only probe for _CPC if CPPC v2 is
 acked

On Thu, Jun 30, 2022 at 09:25:27PM -0500, Mario Limonciello wrote:
> Previously the kernel used to ignore whether the firmware masked CPPC
> or CPPCv2 and would just pretend that it worked.
> 
> When support for the USB4 bit in _OSC was introduced from commit
> 9e1f561afb ("ACPI: Execute platform _OSC also with query bit clear")
> the kernel began to look at the return when the query bit was clear.
> 
> This caused regressions that were misdiagnosed and attempted to be solved
> as part of commit 2ca8e6285250 ("Revert "ACPI: Pass the same capabilities
> to the _OSC regardless of the query flag""). This caused a different
> regression where non-Intel systems weren't able to negotiate _OSC
> properly.
> 
> This was reverted in commit 2ca8e6285250 ("Revert "ACPI: Pass the same
> capabilities to the _OSC regardless of the query flag"") and attempted to
> be fixed by commit c42fa24b4475 ("ACPI: bus: Avoid using CPPC if not
> supported by firmware") but the regression still returned.
> 
> These systems with the regression only load support for CPPC from an SSDT
> dynamically when _OSC reports CPPC v2.  Avoid the problem by not letting
> CPPC satisfy the requirement in `acpi_cppc_processor_probe`.
> 
> Reported-by: CUI Hao <cuihao.leo@...il.com>
> Reported-by: maxim.novozhilov@...il.com
> Reported-by: lethe.tree@...tonmail.com
> Reported-by: garystephenwright@...il.com
> Reported-by: galaxyking0419@...il.com
> Fixes: c42fa24b4475 ("ACPI: bus: Avoid using CPPC if not supported by firmware")
> Fixes: 2ca8e6285250 ("Revert "ACPI Pass the same capabilities to the _OSC regardless of the query flag"")
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=213023
> Link: https://bugzilla.redhat.com/show_bug.cgi?id=2075387
> Signed-off-by: Mario Limonciello <mario.limonciello@....com>

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