linux-kernel - Re: [PATCH v5 2/2] bus: mhi: core: Move to polling method to wait for MHI ready

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Date:   Wed, 31 Mar 2021 10:23:04 -0700
From:   Bhaumik Bhatt <bbhatt@...eaurora.org>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc:     linux-arm-msm@...r.kernel.org, hemantk@...eaurora.org,
        jhugo@...eaurora.org, linux-kernel@...r.kernel.org,
        carl.yin@...ctel.com, naveen.kumar@...ctel.com,
        loic.poulain@...aro.org
Subject: Re: [PATCH v5 2/2] bus: mhi: core: Move to polling method to wait for
 MHI ready

On 2021-03-31 06:04 AM, Manivannan Sadhasivam wrote:
> On Mon, Mar 29, 2021 at 12:53:03PM -0700, Bhaumik Bhatt wrote:
>> In certain devices, it is likely that there is no incoming MHI
>> interrupt for a transition to MHI READY state. One such example
>> is the move from Pass Through to an SBL or AMSS execution
>> environment. In order to facilitate faster bootup times as there
>> is no need to wait until timeout_ms completes, MHI host can poll
>> every 25 milliseconds to check if device has entered MHI READY
>> until a maximum timeout of twice the timeout_ms is reached.
>> 
>> Signed-off-by: Bhaumik Bhatt <bbhatt@...eaurora.org>
>> ---
>>  drivers/bus/mhi/core/pm.c | 32 +++++++++++++++-----------------
>>  1 file changed, 15 insertions(+), 17 deletions(-)
>> 
>> diff --git a/drivers/bus/mhi/core/pm.c b/drivers/bus/mhi/core/pm.c
>> index 681960c..dcc7fe0 100644
>> --- a/drivers/bus/mhi/core/pm.c
>> +++ b/drivers/bus/mhi/core/pm.c
>> @@ -153,34 +153,32 @@ static void mhi_toggle_dev_wake(struct 
>> mhi_controller *mhi_cntrl)
>>  /* Handle device ready state transition */
>>  int mhi_ready_state_transition(struct mhi_controller *mhi_cntrl)
>>  {
>> -	void __iomem *base = mhi_cntrl->regs;
>>  	struct mhi_event *mhi_event;
>>  	enum mhi_pm_state cur_state;
>>  	struct device *dev = &mhi_cntrl->mhi_dev->dev;
>> -	u32 reset = 1, ready = 0;
>> +	u32 interval_us = 25000; /* poll register field every 25 
>> milliseconds */
>>  	int ret, i;
>> 
>> -	/* Wait for RESET to be cleared and READY bit to be set by the 
>> device */
>> -	wait_event_timeout(mhi_cntrl->state_event,
>> -			   MHI_PM_IN_FATAL_STATE(mhi_cntrl->pm_state) ||
>> -			   mhi_read_reg_field(mhi_cntrl, base, MHICTRL,
>> -					      MHICTRL_RESET_MASK,
>> -					      MHICTRL_RESET_SHIFT, &reset) ||
>> -			   mhi_read_reg_field(mhi_cntrl, base, MHISTATUS,
>> -					      MHISTATUS_READY_MASK,
>> -					      MHISTATUS_READY_SHIFT, &ready) ||
>> -			   (!reset && ready),
>> -			   msecs_to_jiffies(mhi_cntrl->timeout_ms));
>> -
>>  	/* Check if device entered error state */
>>  	if (MHI_PM_IN_FATAL_STATE(mhi_cntrl->pm_state)) {
>>  		dev_err(dev, "Device link is not accessible\n");
>>  		return -EIO;
>>  	}
>> 
>> -	/* Timeout if device did not transition to ready state */
>> -	if (reset || !ready) {
>> -		dev_err(dev, "Device Ready timeout\n");
>> +	/* Wait for RESET to be cleared and READY bit to be set by the 
>> device */
>> +	ret = mhi_poll_reg_field(mhi_cntrl, mhi_cntrl->regs, MHICTRL,
>> +				 MHICTRL_RESET_MASK, MHICTRL_RESET_SHIFT, 0,
>> +				 interval_us);
>> +	if (ret) {
>> +		dev_err(dev, "Device failed to clear MHI Reset\n");
>> +		return -ETIMEDOUT;
> 
> You should return the actual error code since there are couple of error
> paths.
> 
> Thanks,
> Mani
> 
Sure. With the update on patch #1, this will be taken care of properly 
as we
return -ETIMEDOUT from the API.
>> +	}
>> +
>> +	ret = mhi_poll_reg_field(mhi_cntrl, mhi_cntrl->regs, MHISTATUS,
>> +				 MHISTATUS_READY_MASK, MHISTATUS_READY_SHIFT, 1,
>> +				 interval_us);
>> +	if (ret) {
>> +		dev_err(dev, "Device failed to enter MHI Ready\n");
>>  		return -ETIMEDOUT;
>>  	}
>> 
>> --
>> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora 
>> Forum,
>> a Linux Foundation Collaborative Project
>> 

Thanks,
Bhaumik
---
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora 
Forum,
a Linux Foundation Collaborative Project