linux-kernel - Re: [PATCH v3 2/3] bus: mhi: core: Move to polling method to wait for MHI ready

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Date:   Wed, 10 Mar 2021 14:58:39 -0800
From:   Bhaumik Bhatt <bbhatt@...eaurora.org>
To:     Jeffrey Hugo <jhugo@...eaurora.org>
Cc:     manivannan.sadhasivam@...aro.org, linux-arm-msm@...r.kernel.org,
        hemantk@...eaurora.org, linux-kernel@...r.kernel.org,
        loic.poulain@...aro.org, carl.yin@...ctel.com,
        naveen.kumar@...ctel.com
Subject: Re: [PATCH v3 2/3] bus: mhi: core: Move to polling method to wait for
 MHI ready

On 2021-03-10 11:02 AM, Jeffrey Hugo wrote:
> On 2/23/2021 8:44 PM, 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 | 31 ++++++++++++++-----------------
>>   1 file changed, 14 insertions(+), 17 deletions(-)
>> 
>> diff --git a/drivers/bus/mhi/core/pm.c b/drivers/bus/mhi/core/pm.c
>> index 681960c..5fe33d4 100644
>> --- a/drivers/bus/mhi/core/pm.c
>> +++ b/drivers/bus/mhi/core/pm.c
>> @@ -153,34 +153,31 @@ 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;
>>   	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,
>> +				 25000);
>> +	if (ret) {
>> +		dev_err(dev, "Device failed to clear MHI Reset\n");
>> +		return -ETIMEDOUT;
>> +	}
>> +
>> +	ret = mhi_poll_reg_field(mhi_cntrl, mhi_cntrl->regs, MHISTATUS,
>> +				 MHISTATUS_READY_MASK, MHISTATUS_READY_SHIFT, 1,
>> +				 25000);
> 
> You use the magic number "25000" twice here.  Its my understanding
> that the preference is to inline a magic number if its used in one
> spot, but use a macro if its used more than that.
> 
> Both uses are confined to this function, and in close proximity, so
> chances that one gets updated without the other seem minimal, so this
> feels like a borderline case.  I don't know if Mani has an opinion
> here.
> 
> I'd probably err on the side of making a macro or a single variable.
> If not, I think some comments explaining the value are warranted
> (should comment the macro as well).
> 
I think just using a variable would be good enough here. I can add a 
comment
when defining the interval variable.
>> +	if (ret) {
>> +		dev_err(dev, "Device failed to enter MHI Ready\n");
>>   		return -ETIMEDOUT;
>>   	}
>> 

Thanks,
Bhaumik
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