linux-kernel - [PATCH v4 2/6] bus: mhi: host: pci_generic: Read SUBSYSTEM_VENDOR

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Message-ID: <20250912-uevent_vdev_next-20250911-v4-2-fa2f6ccd301b@quicinc.com>
Date: Fri, 12 Sep 2025 18:18:06 +0530
From: Vivek.Pernamitta@...cinc.com
To: Manivannan Sadhasivam <mani@...nel.org>
CC: <mhi@...ts.linux.dev>, <linux-arm-msm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        Vivek Pernamitta <quic_vpernami@...cinc.com>,
        Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
Subject: [PATCH v4 2/6] bus: mhi: host: pci_generic: Read
 SUBSYSTEM_VENDOR_ID for VF's to check status

From: Vivek Pernamitta <quic_vpernami@...cinc.com>

In SR-IOV enabled devices, reading the VF DEVICE/VENDOR ID register
returns `FFFFh`, as specified in section 3.4.1.1 of the PCIe SR-IOV spec.
To accurately determine device activity, read the PCIe VENDOR_ID of
the Physical Function (PF) instead.
Health check monitoring for Virtual Functions (VFs) has been disabled,
since VFs are not physical functions and lack direct hardware control.
This change prevents unnecessary CPU cycles from being consumed by VF
health checks, which are both unintended and non-functional.

Signed-off-by: Vivek Pernamitta <quic_vpernami@...cinc.com>
Reviewed-by: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
---
 drivers/bus/mhi/host/pci_generic.c | 34 ++++++++++++++++++++++++----------
 1 file changed, 24 insertions(+), 10 deletions(-)

diff --git a/drivers/bus/mhi/host/pci_generic.c b/drivers/bus/mhi/host/pci_generic.c
index 8a605cb3b8e1e54ef4e699700f3f2660ad5cb093..6fa16975e320212a50e0b68ddb34db5ce711589c 100644
--- a/drivers/bus/mhi/host/pci_generic.c
+++ b/drivers/bus/mhi/host/pci_generic.c
@@ -1082,7 +1082,7 @@ static bool mhi_pci_is_alive(struct mhi_controller *mhi_cntrl)
 	struct pci_dev *pdev = to_pci_dev(mhi_cntrl->cntrl_dev);
 	u16 vendor = 0;
 
-	if (pci_read_config_word(pdev, PCI_VENDOR_ID, &vendor))
+	if (pci_read_config_word(pci_physfn(pdev), PCI_VENDOR_ID, &vendor))
 		return false;
 
 	if (vendor == (u16) ~0 || vendor == 0)
@@ -1193,7 +1193,9 @@ static void mhi_pci_recovery_work(struct work_struct *work)
 
 	dev_warn(&pdev->dev, "device recovery started\n");
 
-	timer_delete(&mhi_pdev->health_check_timer);
+	if (pdev->is_physfn)
+		timer_delete(&mhi_pdev->health_check_timer);
+
 	pm_runtime_forbid(&pdev->dev);
 
 	/* Clean up MHI state */
@@ -1220,7 +1222,10 @@ static void mhi_pci_recovery_work(struct work_struct *work)
 	dev_dbg(&pdev->dev, "Recovery completed\n");
 
 	set_bit(MHI_PCI_DEV_STARTED, &mhi_pdev->status);
-	mod_timer(&mhi_pdev->health_check_timer, jiffies + HEALTH_CHECK_PERIOD);
+
+	if (pdev->is_physfn)
+		mod_timer(&mhi_pdev->health_check_timer, jiffies + HEALTH_CHECK_PERIOD);
+
 	return;
 
 err_unprepare:
@@ -1307,7 +1312,9 @@ static int mhi_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
 	else
 		mhi_cntrl_config = info->config;
 
-	timer_setup(&mhi_pdev->health_check_timer, health_check, 0);
+	/* Initialize health check monitor only for Physical functions */
+	if (pdev->is_physfn)
+		timer_setup(&mhi_pdev->health_check_timer, health_check, 0);
 
 	mhi_cntrl = &mhi_pdev->mhi_cntrl;
 
@@ -1371,7 +1378,8 @@ static int mhi_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
 	set_bit(MHI_PCI_DEV_STARTED, &mhi_pdev->status);
 
 	/* start health check */
-	mod_timer(&mhi_pdev->health_check_timer, jiffies + HEALTH_CHECK_PERIOD);
+	if (pdev->is_physfn)
+		mod_timer(&mhi_pdev->health_check_timer, jiffies + HEALTH_CHECK_PERIOD);
 
 	/* Allow runtime suspend only if both PME from D3Hot and M3 are supported */
 	if (pci_pme_capable(pdev, PCI_D3hot) && !(info->no_m3)) {
@@ -1396,7 +1404,8 @@ static void mhi_pci_remove(struct pci_dev *pdev)
 	struct mhi_pci_device *mhi_pdev = pci_get_drvdata(pdev);
 	struct mhi_controller *mhi_cntrl = &mhi_pdev->mhi_cntrl;
 
-	timer_delete_sync(&mhi_pdev->health_check_timer);
+	if (pdev->is_physfn)
+		timer_delete_sync(&mhi_pdev->health_check_timer);
 	cancel_work_sync(&mhi_pdev->recovery_work);
 
 	if (test_and_clear_bit(MHI_PCI_DEV_STARTED, &mhi_pdev->status)) {
@@ -1424,7 +1433,8 @@ static void mhi_pci_reset_prepare(struct pci_dev *pdev)
 
 	dev_info(&pdev->dev, "reset\n");
 
-	timer_delete(&mhi_pdev->health_check_timer);
+	if (pdev->is_physfn)
+		timer_delete(&mhi_pdev->health_check_timer);
 
 	/* Clean up MHI state */
 	if (test_and_clear_bit(MHI_PCI_DEV_STARTED, &mhi_pdev->status)) {
@@ -1469,7 +1479,8 @@ static void mhi_pci_reset_done(struct pci_dev *pdev)
 	}
 
 	set_bit(MHI_PCI_DEV_STARTED, &mhi_pdev->status);
-	mod_timer(&mhi_pdev->health_check_timer, jiffies + HEALTH_CHECK_PERIOD);
+	if (pdev->is_physfn)
+		mod_timer(&mhi_pdev->health_check_timer, jiffies + HEALTH_CHECK_PERIOD);
 }
 
 static pci_ers_result_t mhi_pci_error_detected(struct pci_dev *pdev,
@@ -1534,7 +1545,9 @@ static int  __maybe_unused mhi_pci_runtime_suspend(struct device *dev)
 	if (test_and_set_bit(MHI_PCI_DEV_SUSPENDED, &mhi_pdev->status))
 		return 0;
 
-	timer_delete(&mhi_pdev->health_check_timer);
+	if (pdev->is_physfn)
+		timer_delete(&mhi_pdev->health_check_timer);
+
 	cancel_work_sync(&mhi_pdev->recovery_work);
 
 	if (!test_bit(MHI_PCI_DEV_STARTED, &mhi_pdev->status) ||
@@ -1585,7 +1598,8 @@ static int __maybe_unused mhi_pci_runtime_resume(struct device *dev)
 	}
 
 	/* Resume health check */
-	mod_timer(&mhi_pdev->health_check_timer, jiffies + HEALTH_CHECK_PERIOD);
+	if (pdev->is_physfn)
+		mod_timer(&mhi_pdev->health_check_timer, jiffies + HEALTH_CHECK_PERIOD);
 
 	/* It can be a remote wakeup (no mhi runtime_get), update access time */
 	pm_runtime_mark_last_busy(dev);

-- 
2.34.1