linux-kernel - [PATCH 1/2] ACPI: processor: idle: Return an error if both P

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Message-ID: <20250328143040.9348-1-ggherdovich@suse.cz>
Date: Fri, 28 Mar 2025 15:30:39 +0100
From: Giovanni Gherdovich <ggherdovich@...e.cz>
To: "Rafael J . Wysocki" <rafael@...nel.org>,
	Zhang Rui <rui.zhang@...el.com>
Cc: Len Brown <lenb@...nel.org>,
	Giovanni Gherdovich <ggherdovich@...e.cz>,
	linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org
Subject: [PATCH 1/2] ACPI: processor: idle: Return an error if both P_LVL{2,3} idle states are invalid

Prior to commit 496121c02127e9c460b436244c38260b044cc45a ("ACPI: processor:
idle: Allow probing on platforms with one ACPI C-state"), the acpi_idle
driver wouldn't load on systems without a valid C-State at least as deep
as C2. The behavior was desirable for guests on hypervisors such as VMWare
ESXi, which by default don't have the _CST ACPI method, and set the C2 and
C3 latencies to 101 and 1001 microseconds respectively via the FADT, to
signify they're unsupported.

Since the above change though, these virtualized deployments end up loading
acpi_idle, and thus entering the default C1 C-State set by
acpi_processor_get_power_info_default(); this is undesirable for a system
that's communicating to the OS it doesn't want C-States (missing _CST, and
invalid C2/C3 in FADT).

Make acpi_processor_get_power_info_fadt() return ENODEV in that case, so
that acpi_processor_get_cstate_info() exits early and doesn't set
pr->flags.power = 1.

Fixes: 496121c02127 ("ACPI: processor: idle: Allow probing on platforms with one ACPI C-state")
Signed-off-by: Giovanni Gherdovich <ggherdovich@...e.cz>
---
 drivers/acpi/processor_idle.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
index 586cc7d1d8aa..b181f7fc2090 100644
--- a/drivers/acpi/processor_idle.c
+++ b/drivers/acpi/processor_idle.c
@@ -268,6 +268,10 @@ static int acpi_processor_get_power_info_fadt(struct acpi_processor *pr)
 			 ACPI_CX_DESC_LEN, "ACPI P_LVL3 IOPORT 0x%x",
 			 pr->power.states[ACPI_STATE_C3].address);

+	if (!pr->power.states[ACPI_STATE_C2].address &&
+	    !pr->power.states[ACPI_STATE_C3].address)
+		return -ENODEV;
+
 	return 0;
 }

-- 
2.43.0