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

On 12/1/2025 9:26 PM, Krishna Chaitanya Chundru wrote:
> 
> 
> 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.
ok here we are doing 2 different devices based pm runtime API usage in 
this core MHI driver.
1. mhi_cntrl->dev
2. mhi_cntrl->mhi_dev->dev

Those are seperate devices, and here we are mixing those usage.
Is it correct or I am seeing differently ?

Regards,
Mayank

>>
>> 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.
Ok sounds good.
>>
>> 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);
>>>
>>
>