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

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Date:   Fri, 19 Feb 2021 10:05:54 -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, jhugo=codeaurora.org@...eaurora.org
Subject: Re: [PATCH] bus: mhi: core: Move to polling method to wait for MHI
 ready

On 2021-02-19 06:55 AM, Jeffrey Hugo wrote:
> On 2/18/2021 7:18 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 | 32 ++++++++++++++++----------------
>>   1 file changed, 16 insertions(+), 16 deletions(-)
>> 
>> diff --git a/drivers/bus/mhi/core/pm.c b/drivers/bus/mhi/core/pm.c
>> index 65ebca8..ec0060c 100644
>> --- a/drivers/bus/mhi/core/pm.c
>> +++ b/drivers/bus/mhi/core/pm.c
>> @@ -9,6 +9,7 @@
>>   #include <linux/dma-direction.h>
>>   #include <linux/dma-mapping.h>
>>   #include <linux/interrupt.h>
>> +#include <linux/iopoll.h>
>>   #include <linux/list.h>
>>   #include <linux/mhi.h>
>>   #include <linux/module.h>
>> @@ -157,30 +158,29 @@ int mhi_ready_state_transition(struct 
>> mhi_controller *mhi_cntrl)
>>   	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 reset, ready;
>>   	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 = readl_relaxed_poll_timeout(base + MHICTRL, reset,
>> +					 !(reset & MHICTRL_RESET_MASK), 25000,
>> +					 mhi_cntrl->timeout_ms * 1000);
>> +	if (ret) {
>> +		dev_err(dev, "Device failed to clear MHI Reset\n");
>> +		return -ETIMEDOUT;
>> +	}
>> +
>> +	ret = readl_relaxed_poll_timeout(base + MHISTATUS, ready,
>> +					 (ready & MHISTATUS_READY_MASK), 25000,
>> +					 mhi_cntrl->timeout_ms * 1000);
>> +	if (ret) {
>> +		dev_err(dev, "Device failed to enter MHI Ready\n");
>>   		return -ETIMEDOUT;
>>   	}
>> 
> 
> I think this gets a NACK from me.
> 
> mhi_read_reg_field() uses the controller defined accessor method
> read_reg().  readl_relaxed_poll_timeout() does not.  If, say, MHI was
> implemented over I2C, direct readl() accesses wouldn't be valid, and
> this would break.
> 
> Also, if the link ever goes down in the middle if the timeout, the
> controller read_reg() should detect that, but
> readl_relaxed_poll_timeout() would not.
> 
> I'm fine with this concept, but I think the implementation needs to be 
> adjusted.
I agree. I will think on this and plan it around the controller defined 
method.

Thanks,
Bhaumik
---
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