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

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Message-ID: <65df50b9-0bdf-4a62-ae1f-d0bb550ff406@oss.qualcomm.com>
Date: Mon, 15 Sep 2025 14:22:17 +0530
From: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
To: Vivek.Pernamitta@...cinc.com, 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>
Subject: Re: [PATCH v4 2/6] bus: mhi: host: pci_generic: Read
 SUBSYSTEM_VENDOR_ID for VF's to check status



On 9/12/2025 6:18 PM, Vivek.Pernamitta@...cinc.com wrote:
> 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) insteadcommit text and subject needs to be modified to reflect new changes

> 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))
As you are invoking only for physical functions pci_physfn is not needed.

- Krishna Chaitanya
>   		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);
>