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

On 12/2/2025 12:03 AM, Mayank Rana wrote:
> 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 ?
These API's not only  do runtime_get & put but as also do wake_get & 
wake_put which make sure endpoint also doesn't go M1 state.
>
> 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) ?
M3 are controlled by the controller driver, they usually do it as part 
of their runtime suspend
and M0 as part of runtime resume.
once the mhi driver gives pm_runtime_put() then only controller can go 
keep MHI in M3.
So we can't tie MHI states pm_runtime_get/put.

- Krishna Chaitanya.
>
> 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);
>>
>