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From: "Rafael J. Wysocki" <rjw@rjwysocki.net>
To: Linux PM <linux-pm@vger.kernel.org>,
 Daniel Lezcano <daniel.lezcano@linaro.org>,
 Laura Nao <laura.nao@collabora.com>
Cc: Linux ACPI <linux-acpi@vger.kernel.org>,
 LKML <linux-kernel@vger.kernel.org>, Lukasz Luba <lukasz.luba@arm.com>,
 Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
 Zhang Rui <rui.zhang@intel.com>
Subject:
 [PATCH v3] thermal: core: Do not fail cdev registration because of invalid
 initial state
Date: Thu, 06 Jun 2024 20:14:52 +0200
Message-ID: <12456961.O9o76ZdvQC@kreacher>
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From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Subject: [PATCH v3] thermal: core: Do not fail cdev registration because of invalid initial state

It is reported that commit 31a0fa0019b0 ("thermal/debugfs: Pass cooling
device state to thermal_debug_cdev_add()") causes the ACPI fan driver
to fail probing on some systems which turns out to be due to the _FST
control method returning an invalid value until _FSL is first evaluated
for the given fan.  If this happens, the .get_cur_state() cooling device
callback returns an error and __thermal_cooling_device_register() fails
as uses that callback after commit 31a0fa0019b0.

Arguably, _FST should not return an invalid value even if it is
evaluated before _FSL, so this may be regarded as a platform firmware
issue, but at the same time it is not a good enough reason for failing
the cooling device registration where the initial cooling device state
is only needed to initialize a thermal debug facility.

Accordingly, modify __thermal_cooling_device_register() to avoid
calling thermal_debug_cdev_add() instead of returning an error if the
initial .get_cur_state() callback invocation fails.

Fixes: 31a0fa0019b0 ("thermal/debugfs: Pass cooling device state to thermal_debug_cdev_add()")
Closes: https://lore.kernel.org/linux-acpi/20240530153727.843378-1-laura.nao@collabora.com
Reported-by: Laura Nao <laura.nao@collabora.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---

v2 -> v3:
   * Add a comment to explain the initial state of a cooling device (Daniel).
     No functional changes.

v1 -> v2:
   * Instead of making the thermal debug code effectively ignore the invalid
     initial cooling device state, simply don't register thermal debugfs for
     a cooling device if its initial state returned by the driver's
     .get_cur_state() is invalid (Daniel).

Laura, please test this one even though I don't see why it wouldn't work for
you if the v1 did.

---
 drivers/thermal/thermal_core.c |   13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

Index: linux-pm/drivers/thermal/thermal_core.c
===================================================================
--- linux-pm.orig/drivers/thermal/thermal_core.c
+++ linux-pm/drivers/thermal/thermal_core.c
@@ -999,9 +999,17 @@ __thermal_cooling_device_register(struct
 	if (ret)
 		goto out_cdev_type;
 
+	/*
+	 * The cooling device's current state is only needed for debug
+	 * initialization below, so a failure to get it does not cause
+	 * the entire cooling device initialization to fail.  However,
+	 * the debug will not work for the device if its initial state
+	 * cannot be determined and drivers are responsible for ensuring
+	 * that this will not happen.
+	 */
 	ret = cdev->ops->get_cur_state(cdev, &current_state);
 	if (ret)
-		goto out_cdev_type;
+		current_state = ULONG_MAX;
 
 	thermal_cooling_device_setup_sysfs(cdev);
 
@@ -1016,7 +1024,8 @@ __thermal_cooling_device_register(struct
 		return ERR_PTR(ret);
 	}
 
-	thermal_debug_cdev_add(cdev, current_state);
+	if (current_state <= cdev->max_state)
+		thermal_debug_cdev_add(cdev, current_state);
 
 	/* Add 'this' new cdev to the global cdev list */
 	mutex_lock(&thermal_list_lock);