Re: [PATCH 4/4] bus: mhi: Fix broken runtime PM design

Hi Krishna

On 12/1/2025 4:43 AM, Krishna Chaitanya Chundru wrote:
> The current MHI runtime PM design is flawed, as the MHI core attempts to
> manage power references internally via mhi_queue() and related paths.
> This is problematic because the controller drivers do not have the
> knowledge of the client PM status due to the broken PM topology. So when
> they runtime suspend the controller, the client drivers could no longer
> function.
> 
> To address this, in the new design, the client drivers reports their own
> runtime PM status now and the PM framework makes sure that the parent
> (controller driver) and other components up in the chain remain active.
> This leverages the standard parent-child PM relationship.
> 
> Since MHI creates a mhi_dev device without an associated driver, we
> explicitly enable runtime PM on it and mark it with
> pm_runtime_no_callbacks() to indicate the PM core that no callbacks
> exist for this device. This is only needed for MHI controller, since
> the controller driver uses the bus device just like PCI device.
> 
> Also Update the MHI core to explicitly manage runtime PM references in
> __mhi_device_get_sync() and mhi_device_put() to ensure the controller
> does not enter suspend while a client device is active.
Why does this needed here ?
Isn't it MHI client driver take care of allowing suspend ?
Do you think we should remove mhi_device_get_sync() and mhi_device_put() 
API interfaces as well ? And let controller/client driver takes care of 
calling get/sync directly ?

How are you handling cases for M0 and M3 suspend ?
Do we need to tie runtime usage with M0 (pm_runtime_get) and M3 
(pm_runtime_put) ?

Regards,
Mayank

> Signed-off-by: Krishna Chaitanya Chundru <[email protected]>
> ---
>   drivers/bus/mhi/host/internal.h |  6 +++---
>   drivers/bus/mhi/host/main.c     | 28 ++++------------------------
>   drivers/bus/mhi/host/pm.c       | 18 ++++++++----------
>   3 files changed, 15 insertions(+), 37 deletions(-)
> 
> diff --git a/drivers/bus/mhi/host/internal.h b/drivers/bus/mhi/host/internal.h
> index 61e03298e898e6dd02d2a977cddc4c87b21e3a6c..d6a3168bb3ecc34eab1036c0e74f8d70cf422fed 100644
> --- a/drivers/bus/mhi/host/internal.h
> +++ b/drivers/bus/mhi/host/internal.h
> @@ -355,9 +355,9 @@ static inline bool mhi_is_active(struct mhi_controller *mhi_cntrl)
>   static inline void mhi_trigger_resume(struct mhi_controller *mhi_cntrl)
>   {
>   	pm_wakeup_event(&mhi_cntrl->mhi_dev->dev, 0);
> -	pm_runtime_get(mhi_cntrl->cntrl_dev);
> -	pm_runtime_mark_last_busy(mhi_cntrl->cntrl_dev);
> -	pm_runtime_put(mhi_cntrl->cntrl_dev);
> +	pm_runtime_get(&mhi_cntrl->mhi_dev->dev);
> +	pm_runtime_mark_last_busy(&mhi_cntrl->mhi_dev->dev);
> +	pm_runtime_put(&mhi_cntrl->mhi_dev->dev);
>   }
>   
>   /* Register access methods */
> diff --git a/drivers/bus/mhi/host/main.c b/drivers/bus/mhi/host/main.c
> index 7ac1162a0a81ae11245a2bbd9bf6fd6c0f86fbc1..85a9a5a62a6d3f92b0e9dc35b13fd867db89dd95 100644
> --- a/drivers/bus/mhi/host/main.c
> +++ b/drivers/bus/mhi/host/main.c
> @@ -427,6 +427,8 @@ void mhi_create_devices(struct mhi_controller *mhi_cntrl)
>   		if (ret)
>   			put_device(&mhi_dev->dev);
>   	}
> +	pm_runtime_no_callbacks(&mhi_cntrl->mhi_dev->dev);
> +	devm_pm_runtime_set_active_enabled(&mhi_cntrl->mhi_dev->dev);
>   }
>   
>   irqreturn_t mhi_irq_handler(int irq_number, void *dev)
> @@ -658,12 +660,8 @@ static int parse_xfer_event(struct mhi_controller *mhi_cntrl,
>   			/* notify client */
>   			mhi_chan->xfer_cb(mhi_chan->mhi_dev, &result);
>   
> -			if (mhi_chan->dir == DMA_TO_DEVICE) {
> +			if (mhi_chan->dir == DMA_TO_DEVICE)
>   				atomic_dec(&mhi_cntrl->pending_pkts);
> -				/* Release the reference got from mhi_queue() */
> -				pm_runtime_mark_last_busy(mhi_cntrl->cntrl_dev);
> -				pm_runtime_put(mhi_cntrl->cntrl_dev);
> -			}
>   
>   			/*
>   			 * Recycle the buffer if buffer is pre-allocated,
> @@ -1152,12 +1150,6 @@ static int mhi_queue(struct mhi_device *mhi_dev, struct mhi_buf_info *buf_info,
>   
>   	read_lock_irqsave(&mhi_cntrl->pm_lock, flags);
>   
> -	/* Packet is queued, take a usage ref to exit M3 if necessary
> -	 * for host->device buffer, balanced put is done on buffer completion
> -	 * for device->host buffer, balanced put is after ringing the DB
> -	 */
> -	pm_runtime_get(mhi_cntrl->cntrl_dev);
> -
>   	/* Assert dev_wake (to exit/prevent M1/M2)*/
>   	mhi_cntrl->wake_toggle(mhi_cntrl);
>   
> @@ -1167,11 +1159,6 @@ static int mhi_queue(struct mhi_device *mhi_dev, struct mhi_buf_info *buf_info,
>   	if (likely(MHI_DB_ACCESS_VALID(mhi_cntrl)))
>   		mhi_ring_chan_db(mhi_cntrl, mhi_chan);
>   
> -	if (dir == DMA_FROM_DEVICE) {
> -		pm_runtime_mark_last_busy(mhi_cntrl->cntrl_dev);
> -		pm_runtime_put(mhi_cntrl->cntrl_dev);
> -	}
> -
>   	read_unlock_irqrestore(&mhi_cntrl->pm_lock, flags);
>   
>   	return ret;
> @@ -1377,7 +1364,6 @@ static int mhi_update_channel_state(struct mhi_controller *mhi_cntrl,
>   	ret = mhi_device_get_sync(mhi_cntrl->mhi_dev);
>   	if (ret)
>   		return ret;
> -	pm_runtime_get(mhi_cntrl->cntrl_dev);
>   
>   	reinit_completion(&mhi_chan->completion);
>   	ret = mhi_send_cmd(mhi_cntrl, mhi_chan, cmd);
> @@ -1408,8 +1394,6 @@ static int mhi_update_channel_state(struct mhi_controller *mhi_cntrl,
>   
>   	trace_mhi_channel_command_end(mhi_cntrl, mhi_chan, to_state, TPS("Updated"));
>   exit_channel_update:
> -	pm_runtime_mark_last_busy(mhi_cntrl->cntrl_dev);
> -	pm_runtime_put(mhi_cntrl->cntrl_dev);
>   	mhi_device_put(mhi_cntrl->mhi_dev);
>   
>   	return ret;
> @@ -1592,12 +1576,8 @@ static void mhi_reset_data_chan(struct mhi_controller *mhi_cntrl,
>   	while (tre_ring->rp != tre_ring->wp) {
>   		struct mhi_buf_info *buf_info = buf_ring->rp;
>   
> -		if (mhi_chan->dir == DMA_TO_DEVICE) {
> +		if (mhi_chan->dir == DMA_TO_DEVICE)
>   			atomic_dec(&mhi_cntrl->pending_pkts);
> -			/* Release the reference got from mhi_queue() */
> -			pm_runtime_mark_last_busy(mhi_cntrl->cntrl_dev);
> -			pm_runtime_put(mhi_cntrl->cntrl_dev);
> -		}
>   
>   		if (!buf_info->pre_mapped)
>   			mhi_cntrl->unmap_single(mhi_cntrl, buf_info);
> diff --git a/drivers/bus/mhi/host/pm.c b/drivers/bus/mhi/host/pm.c
> index b4ef115189b505c3450ff0949ad2d09f3ed53386..fd690e8af693109ed8c55248db0ea153f9e69423 100644
> --- a/drivers/bus/mhi/host/pm.c
> +++ b/drivers/bus/mhi/host/pm.c
> @@ -429,6 +429,7 @@ static int mhi_pm_mission_mode_transition(struct mhi_controller *mhi_cntrl)
>   
>   	if (MHI_PM_IN_ERROR_STATE(mhi_cntrl->pm_state)) {
>   		ret = -EIO;
> +		read_unlock_bh(&mhi_cntrl->pm_lock);
>   		goto error_mission_mode;
>   	}
>   
> @@ -459,11 +460,9 @@ static int mhi_pm_mission_mode_transition(struct mhi_controller *mhi_cntrl)
>   	 */
>   	mhi_create_devices(mhi_cntrl);
>   
> -	read_lock_bh(&mhi_cntrl->pm_lock);
>   
>   error_mission_mode:
> -	mhi_cntrl->wake_put(mhi_cntrl, false);
> -	read_unlock_bh(&mhi_cntrl->pm_lock);
> +	mhi_device_put(mhi_cntrl->mhi_dev);
>   
>   	return ret;
>   }
> @@ -1038,9 +1037,11 @@ int __mhi_device_get_sync(struct mhi_controller *mhi_cntrl)
>   		read_unlock_bh(&mhi_cntrl->pm_lock);
>   		return -EIO;
>   	}
> +	read_unlock_bh(&mhi_cntrl->pm_lock);
> +
> +	pm_runtime_get_sync(&mhi_cntrl->mhi_dev->dev);
> +	read_lock_bh(&mhi_cntrl->pm_lock);
>   	mhi_cntrl->wake_get(mhi_cntrl, true);
> -	if (MHI_PM_IN_SUSPEND_STATE(mhi_cntrl->pm_state))
> -		mhi_trigger_resume(mhi_cntrl);
>   	read_unlock_bh(&mhi_cntrl->pm_lock);
>   
>   	ret = wait_event_timeout(mhi_cntrl->state_event,
> @@ -1049,9 +1050,7 @@ int __mhi_device_get_sync(struct mhi_controller *mhi_cntrl)
>   				 msecs_to_jiffies(mhi_cntrl->timeout_ms));
>   
>   	if (!ret || MHI_PM_IN_ERROR_STATE(mhi_cntrl->pm_state)) {
> -		read_lock_bh(&mhi_cntrl->pm_lock);
> -		mhi_cntrl->wake_put(mhi_cntrl, false);
> -		read_unlock_bh(&mhi_cntrl->pm_lock);
> +		mhi_device_put(mhi_cntrl->mhi_dev);
>   		return -EIO;
>   	}
>   
> @@ -1339,11 +1338,10 @@ void mhi_device_put(struct mhi_device *mhi_dev)
>   
>   	mhi_dev->dev_wake--;
>   	read_lock_bh(&mhi_cntrl->pm_lock);
> -	if (MHI_PM_IN_SUSPEND_STATE(mhi_cntrl->pm_state))
> -		mhi_trigger_resume(mhi_cntrl);
>   
>   	mhi_cntrl->wake_put(mhi_cntrl, false);
>   	read_unlock_bh(&mhi_cntrl->pm_lock);
> +	pm_runtime_put(&mhi_cntrl->mhi_dev->dev);
>   }
>   EXPORT_SYMBOL_GPL(mhi_device_put);
>   
>