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

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Message-ID: <20210331130451.GJ15610@work>
Date:   Wed, 31 Mar 2021 18:34:51 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     Bhaumik Bhatt <bbhatt@...eaurora.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 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

> +	}
> +
> +	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
>