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Message-ID: <9d6fa75b-a024-4501-ba26-d9cfb17c8636@quicinc.com>
Date: Fri, 1 Dec 2023 09:08:45 +0800
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Subject: Re: [PATCH RFC v2 1/8] bus: mhi: host: add
 mhi_power_down_no_destroy()
To: Manivannan Sadhasivam <mani@kernel.org>, Kalle Valo <kvalo@kernel.org>
CC: <mhi@lists.linux.dev>, <ath11k@lists.infradead.org>,
        <linux-wireless@vger.kernel.org>
References: <20231127162022.518834-1-kvalo@kernel.org>
 <20231127162022.518834-2-kvalo@kernel.org> <20231130054250.GC3043@thinkpad>
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From: Baochen Qiang <quic_bqiang@quicinc.com>
In-Reply-To: <20231130054250.GC3043@thinkpad>
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On 11/30/2023 1:42 PM, Manivannan Sadhasivam wrote:
> On Mon, Nov 27, 2023 at 06:20:15PM +0200, 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().
>> 	 */
>>
>> 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>
> 
> Any reason for reposting this series without discussing the suggestion from
> Mayank? As I said in the internal thread, this patch breaks the Linux device
> driver model by not destroying the "struct device" when the actual device gets
> removed. We should try to explore alternate options instead of persisting with
> this solution.
> 
> - Mani
I shared my opinion on Mayank's proposal, but not noticed it is in 
internal thead. I will repost here:

Mayank's proposal assumes that at the time PM_POST_HIBERNATION is 
posted, all deferred probe is unblocked and completed, however which is 
not true.

Yes, kernel's sequence is first unblock probe defer and trigger probe 
again, then post PM_POST_HIBERNATION message. But the problem here is 
that the probe-trigger is delegated to an work item and returns 
immediately, kernel does not wait for all probe to complete before 
posting PM_POST_HIBERNATION. So it is not guaranteed that an MHI device 
is probed at the time we get that message.
> 
>> ---
>>   drivers/bus/mhi/host/init.c     |  1 +
>>   drivers/bus/mhi/host/internal.h |  1 +
>>   drivers/bus/mhi/host/pm.c       | 26 +++++++++++++++++++-------
>>   include/linux/mhi.h             | 29 +++++++++++++++++++++++++++--
>>   4 files changed, 48 insertions(+), 9 deletions(-)
>>
>> diff --git a/drivers/bus/mhi/host/init.c b/drivers/bus/mhi/host/init.c
>> index 65ceac1837f9..e626b03ffafa 100644
>> --- a/drivers/bus/mhi/host/init.c
>> +++ b/drivers/bus/mhi/host/init.c
>> @@ -43,6 +43,7 @@ const char * const dev_state_tran_str[DEV_ST_TRANSITION_MAX] = {
>>   	[DEV_ST_TRANSITION_FP] = "FLASH PROGRAMMER",
>>   	[DEV_ST_TRANSITION_SYS_ERR] = "SYS ERROR",
>>   	[DEV_ST_TRANSITION_DISABLE] = "DISABLE",
>> +	[DEV_ST_TRANSITION_DISABLE_DESTROY_DEVICE] = "DISABLE (DESTROY DEVICE)",
>>   };
>>   
>>   const char * const mhi_ch_state_type_str[MHI_CH_STATE_TYPE_MAX] = {
>> diff --git a/drivers/bus/mhi/host/internal.h b/drivers/bus/mhi/host/internal.h
>> index 30ac415a3000..3f45c9c447bd 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 a2f2feef1476..8833b0248393 100644
>> --- a/drivers/bus/mhi/host/pm.c
>> +++ b/drivers/bus/mhi/host/pm.c
>> @@ -458,7 +458,8 @@ 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;
>> @@ -520,8 +521,10 @@ 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);
>>   
>> @@ -806,7 +809,10 @@ 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;
>> @@ -1160,7 +1166,8 @@ 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;
>> @@ -1196,14 +1203,19 @@ 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 d0f9b522f328..ae092bc8b97e 100644
>> --- a/include/linux/mhi.h
>> +++ b/include/linux/mhi.h
>> @@ -648,12 +648,37 @@ 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
>> -- 
>> 2.39.2
>>
>>
>