linux-kernel - [PATCH] pm: sleep: do not set is_prepared when no_pm

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Message-Id: <20240902125933.5742-1-00107082@163.com>
Date: Mon,  2 Sep 2024 20:59:33 +0800
From: David Wang <00107082@....com>
To: rafael@...nel.org,
	pavel@....cz,
	gregkh@...uxfoundation.org
Cc: linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	David Wang <00107082@....com>
Subject: [PATCH] pm: sleep: do not set is_prepared when no_pm_callbacks is set

When resume, a parent device with no pm callbacks
would have "is_prepared" and "direct_complete" bit
set, and skip the "fib" chance to unset "is_prepared"
in device_resume because of the direct_complete bit.
This will trigger a kernel warning when resume its child
For example, when suspend system with an USB webcam
opened, following warning would show up during resume:

 >usb 3-1.1: reset high-speed USB device number 4 using xhci_hcd
 >..
 >ep_81: PM: parent 3-1.1:1.1 should not be sleeping

The device parenting relationships are:
[usb 3-1.1] << [uvcvideo 3-1.1:1.1] << [ep_81].
When resume, since the virtual [uvcvideo 3-1.1:1.1] device
has no pm callbacks, it would not clear "is_prepared"
once set.  Then, when resume [ep_81], pm module would
yield a warn seeing [ep_81]'s parent [uvcvideo 3-1.1:1.1]
having "is_prepared".

Do not set "is_prepared" for virtual devices having
no pm callbacks can clear those kernel warnings.

Signed-off-by: David Wang <00107082@....com>
---
 drivers/base/power/main.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
index 934e5bb61f13..e2149ccf2c3e 100644
--- a/drivers/base/power/main.c
+++ b/drivers/base/power/main.c
@@ -1880,7 +1880,8 @@ int dpm_prepare(pm_message_t state)
 		mutex_lock(&dpm_list_mtx);

 		if (!error) {
-			dev->power.is_prepared = true;
+			if (!dev->power.no_pm_callbacks)
+				dev->power.is_prepared = true;
 			if (!list_empty(&dev->power.entry))
 				list_move_tail(&dev->power.entry, &dpm_prepared_list);
 		} else if (error == -EAGAIN) {
-- 
2.39.2