[PATCH] bus: mhi: host: pci_generic: Fix runtime PM imbalance for no_m3 devices

[Alexandra Lu]

mhi_pci_probe() drops the runtime PM reference taken by local_pci_probe()
only when the device supports both PME from D3hot and M3, but
mhi_pci_remove() re-takes it based on PME capability alone, without
checking no_m3.

For a device that is PME capable and has no_m3 set, probe therefore never
drops the reference while remove takes an extra one, leaving the runtime
PM usage count one higher after every bind/unbind cycle.  That is benign
for the device being removed, since the PCI core resumes it to D0 on
unbind regardless, but the struct device outlives the binding, so the
count accumulates across repeated cycles and can end up preventing
runtime suspend altogether.

Cache no_m3 in the driver's private data, as is already done for
reset_on_remove, and gate the removal side on it as well.  Unlike
reset_on_remove it is cached for virtual functions too, because the probe
side gate tests info->no_m3 for physical and virtual functions alike.

QDU100 is currently the only device that sets no_m3.

Fixes: 0494cf9793b7 ("bus: mhi: host: pci_generic: Disable runtime PM for QDU100")
Assisted-by: Cursor:claude-opus-5
Signed-off-by: Alexandra Lu <alexandra.lu@xxxxxxxxx>
---
 drivers/bus/mhi/host/pci_generic.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/bus/mhi/host/pci_generic.c b/drivers/bus/mhi/host/pci_generic.c
index b636e2c23b4d..eda00a2e242c 100644
--- a/drivers/bus/mhi/host/pci_generic.c
+++ b/drivers/bus/mhi/host/pci_generic.c
@@ -1097,6 +1097,7 @@ struct mhi_pci_device {
 	struct work_struct recovery_work;
 	struct timer_list health_check_timer;
 	unsigned long status;
+	bool no_m3;
 	bool reset_on_remove;
 };
 
@@ -1409,6 +1410,8 @@ static int mhi_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
 	mhi_cntrl->mru = info->mru_default;
 	mhi_cntrl->name = info->name;
 
+	mhi_pdev->no_m3 = info->no_m3;
+
 	if (!pdev->is_virtfn)
 		mhi_pdev->reset_on_remove = info->reset_on_remove;
 
@@ -1497,7 +1500,7 @@ static void mhi_pci_remove(struct pci_dev *pdev)
 	}
 
 	/* balancing probe put_noidle */
-	if (pci_pme_capable(pdev, PCI_D3hot))
+	if (pci_pme_capable(pdev, PCI_D3hot) && !mhi_pdev->no_m3)
 		pm_runtime_get_noresume(&pdev->dev);
 
 	if (mhi_pdev->reset_on_remove)
-- 
2.43.0