[RFC,1/8] bus: mhi: host: add mhi_power_down_no_destroy()

From: Baochen Qiang <quic_bqiang@quicinc.com>

If ath11k tries to call mhi_power_up() during resume it fails:

ath11k_pci 0000:06:00.0: timeout while waiting for restart complete

This happens because when calling mhi_power_up() the MHI subsystem eventually
calls device_add() from mhi_create_devices() but the device creation is
deferred:

mhi mhi0_IPCR: Driver qcom_mhi_qrtr force probe deferral

The reason for deferring device creation is explained in dpm_prepare():

	/*
	 * It is unsafe if probing of devices will happen during suspend or
	 * hibernation and system behavior will be unpredictable in this case.
	 * So, let's prohibit device's probing here and defer their probes
	 * instead. The normal behavior will be restored in dpm_complete().
	 */

Because the device probe is deferred, the qcom_mhi_qrtr_probe() is not called and
qcom_mhi_qrtr_dl_callback() fails silently as qdev is zero:

static void qcom_mhi_qrtr_dl_callback(struct mhi_device *mhi_dev,
				      struct mhi_result *mhi_res)
{
	struct qrtr_mhi_dev *qdev = dev_get_drvdata(&mhi_dev->dev);
	int rc;

	if (!qdev || mhi_res->transaction_status)
		return;

So what this means that QRTR is not delivering messages and the QMI connection
is not working between ath11k and the firmware, resulting a failure in firmware
initialisation.

To fix this add new function mhi_power_down_no_destroy() which does not destroy
the devices during power down. This way mhi_power_up() can be called during
resume and we can get ath11k hibernation working with the following patches.

Tested-on: WCN6855 hw2.0 PCI WLAN.HSP.1.1-03125-QCAHSPSWPL_V1_V2_SILICONZ_LITE-3.6510.30

Signed-off-by: Baochen Qiang <quic_bqiang@quicinc.com>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
---
 drivers/bus/mhi/host/internal.h |  1 +
 drivers/bus/mhi/host/pm.c       | 26 +++++++++++++++++++-------
 include/linux/mhi.h             | 29 +++++++++++++++++++++++++++--
 3 files changed, 47 insertions(+), 9 deletions(-)

On 11/10/2023 2:21 AM, Kalle Valo wrote:
> From: Baochen Qiang <quic_bqiang@quicinc.com>
> 
> If ath11k tries to call mhi_power_up() during resume it fails:
> 
> ath11k_pci 0000:06:00.0: timeout while waiting for restart complete
> 
> This happens because when calling mhi_power_up() the MHI subsystem eventually
> calls device_add() from mhi_create_devices() but the device creation is
> deferred:
> 
> mhi mhi0_IPCR: Driver qcom_mhi_qrtr force probe deferral
> 
> The reason for deferring device creation is explained in dpm_prepare():
> 
> 	/*
> 	 * It is unsafe if probing of devices will happen during suspend or
> 	 * hibernation and system behavior will be unpredictable in this case.
> 	 * So, let's prohibit device's probing here and defer their probes
> 	 * instead. The normal behavior will be restored in dpm_complete().
> 	 */
have you consider registering for pm_notifier callback specifically for 
PM_POST_HIBERNATION (Documentation/power/notifiers.txt), and then making 
decision of calling MHI power up sequence which would make sure that 
created device based driver probe() is completed.
> 
> Because the device probe is deferred, the qcom_mhi_qrtr_probe() is not called and
> qcom_mhi_qrtr_dl_callback() fails silently as qdev is zero:
> 
> static void qcom_mhi_qrtr_dl_callback(struct mhi_device *mhi_dev,
> 				      struct mhi_result *mhi_res)
> {
> 	struct qrtr_mhi_dev *qdev = dev_get_drvdata(&mhi_dev->dev);
> 	int rc;
> 
> 	if (!qdev || mhi_res->transaction_status)
> 		return;
> 
> So what this means that QRTR is not delivering messages and the QMI connection
> is not working between ath11k and the firmware, resulting a failure in firmware
> initialisation.
> 
> To fix this add new function mhi_power_down_no_destroy() which does not destroy
> the devices during power down. This way mhi_power_up() can be called during
> resume and we can get ath11k hibernation working with the following patches.
> 
> Tested-on: WCN6855 hw2.0 PCI WLAN.HSP.1.1-03125-QCAHSPSWPL_V1_V2_SILICONZ_LITE-3.6510.30
> 
> Signed-off-by: Baochen Qiang <quic_bqiang@quicinc.com>
> Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
> ---
>   drivers/bus/mhi/host/internal.h |  1 +
>   drivers/bus/mhi/host/pm.c       | 26 +++++++++++++++++++-------
>   include/linux/mhi.h             | 29 +++++++++++++++++++++++++++--
>   3 files changed, 47 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/bus/mhi/host/internal.h b/drivers/bus/mhi/host/internal.h
> index 2e139e76de4c..d1033af285e2 100644
> --- a/drivers/bus/mhi/host/internal.h
> +++ b/drivers/bus/mhi/host/internal.h
> @@ -69,6 +69,7 @@ enum dev_st_transition {
>   	DEV_ST_TRANSITION_FP,
>   	DEV_ST_TRANSITION_SYS_ERR,
>   	DEV_ST_TRANSITION_DISABLE,
> +	DEV_ST_TRANSITION_DISABLE_DESTROY_DEVICE,
>   	DEV_ST_TRANSITION_MAX,
>   };
>   
> diff --git a/drivers/bus/mhi/host/pm.c b/drivers/bus/mhi/host/pm.c
> index 8a4362d75fc4..e0e429adbda6 100644
> --- a/drivers/bus/mhi/host/pm.c
> +++ b/drivers/bus/mhi/host/pm.c
> @@ -453,7 +453,8 @@ static int mhi_pm_mission_mode_transition(struct mhi_controller *mhi_cntrl)
>   }
>   
>   /* Handle shutdown transitions */
> -static void mhi_pm_disable_transition(struct mhi_controller *mhi_cntrl)
> +static void mhi_pm_disable_transition(struct mhi_controller *mhi_cntrl,
> +				      bool destroy_device)
>   {
>   	enum mhi_pm_state cur_state;
>   	struct mhi_event *mhi_event;
> @@ -515,8 +516,10 @@ static void mhi_pm_disable_transition(struct mhi_controller *mhi_cntrl)
>   	dev_dbg(dev, "Waiting for all pending threads to complete\n");
>   	wake_up_all(&mhi_cntrl->state_event);
>   
> -	dev_dbg(dev, "Reset all active channels and remove MHI devices\n");
> -	device_for_each_child(&mhi_cntrl->mhi_dev->dev, NULL, mhi_destroy_device);
> +	if (destroy_device) {
> +		dev_dbg(dev, "Reset all active channels and remove MHI devices\n");
> +		device_for_each_child(&mhi_cntrl->mhi_dev->dev, NULL, mhi_destroy_device);
> +	}
>   
>   	mutex_lock(&mhi_cntrl->pm_mutex);
>   
> @@ -801,7 +804,10 @@ void mhi_pm_st_worker(struct work_struct *work)
>   			mhi_pm_sys_error_transition(mhi_cntrl);
>   			break;
>   		case DEV_ST_TRANSITION_DISABLE:
> -			mhi_pm_disable_transition(mhi_cntrl);
> +			mhi_pm_disable_transition(mhi_cntrl, false);
> +			break;
> +		case DEV_ST_TRANSITION_DISABLE_DESTROY_DEVICE:
> +			mhi_pm_disable_transition(mhi_cntrl, true);
>   			break;
>   		default:
>   			break;
> @@ -1154,7 +1160,8 @@ int mhi_async_power_up(struct mhi_controller *mhi_cntrl)
>   }
>   EXPORT_SYMBOL_GPL(mhi_async_power_up);
>   
> -void mhi_power_down(struct mhi_controller *mhi_cntrl, bool graceful)
> +void __mhi_power_down(struct mhi_controller *mhi_cntrl, bool graceful,
> +		      bool destroy_device)
>   {
>   	enum mhi_pm_state cur_state, transition_state;
>   	struct device *dev = &mhi_cntrl->mhi_dev->dev;
> @@ -1190,14 +1197,19 @@ void mhi_power_down(struct mhi_controller *mhi_cntrl, bool graceful)
>   	write_unlock_irq(&mhi_cntrl->pm_lock);
>   	mutex_unlock(&mhi_cntrl->pm_mutex);
>   
> -	mhi_queue_state_transition(mhi_cntrl, DEV_ST_TRANSITION_DISABLE);
> +	if (destroy_device)
> +		mhi_queue_state_transition(mhi_cntrl,
> +					   DEV_ST_TRANSITION_DISABLE_DESTROY_DEVICE);
> +	else
> +		mhi_queue_state_transition(mhi_cntrl,
> +					   DEV_ST_TRANSITION_DISABLE);
>   
>   	/* Wait for shutdown to complete */
>   	flush_work(&mhi_cntrl->st_worker);
>   
>   	disable_irq(mhi_cntrl->irq[0]);
>   }
> -EXPORT_SYMBOL_GPL(mhi_power_down);
> +EXPORT_SYMBOL_GPL(__mhi_power_down);
>   
>   int mhi_sync_power_up(struct mhi_controller *mhi_cntrl)
>   {
> diff --git a/include/linux/mhi.h b/include/linux/mhi.h
> index 039943ec4d4e..85edc9c5df88 100644
> --- a/include/linux/mhi.h
> +++ b/include/linux/mhi.h
> @@ -644,12 +644,37 @@ int mhi_async_power_up(struct mhi_controller *mhi_cntrl);
>    */
>   int mhi_sync_power_up(struct mhi_controller *mhi_cntrl);
>   
> +void __mhi_power_down(struct mhi_controller *mhi_cntrl, bool graceful,
> +		    bool destroy_device);
> +
>   /**
> - * mhi_power_down - Start MHI power down sequence
> + * mhi_power_down - Start MHI power down sequence. See also
> + * mhi_power_down_no_destroy() which is a variant of this for suspend.
> + *
>    * @mhi_cntrl: MHI controller
>    * @graceful: Link is still accessible, so do a graceful shutdown process
>    */
> -void mhi_power_down(struct mhi_controller *mhi_cntrl, bool graceful);
> +static inline void mhi_power_down(struct mhi_controller *mhi_cntrl, bool graceful)
> +{
> +	__mhi_power_down(mhi_cntrl, graceful, true);
> +}
> +
> +/**
> + * mhi_power_down_no_destroy - Start MHI power down sequence but don't
> + * destroy struct devices. This is a variant for mhi_power_down() and is a
> + * workaround to make it possible to use mhi_power_up() in a resume
> + * handler. When using this variant the caller must also call
> + * mhi_prepare_all_for_transfer_autoqueue() and
> + * mhi_unprepare_all_from_transfer().
> + *
> + * @mhi_cntrl: MHI controller
> + * @graceful: Link is still accessible, so do a graceful shutdown process
> + */
> +static inline void mhi_power_down_no_destroy(struct mhi_controller *mhi_cntrl,
> +					     bool graceful)
> +{
> +	__mhi_power_down(mhi_cntrl, graceful, false);
> +}
>   
>   /**
>    * mhi_unprepare_after_power_down - Free any allocated memory after power down