Re: [PATCH v2] bus: mhi: Fix race while handling SYS_ERR at power up

[Bhaumik Bhatt <bbhatt@codeaurora.org>]

On 2021-11-08 09:49 AM, Manivannan Sadhasivam wrote:
> Some devices tend to trigger SYS_ERR interrupt while the host handling
> SYS_ERR state of the device during power up. This creates a race
> condition and causes a failure in booting up the device.
> 
> The issue is seen on the Sierra Wireless EM9191 modem during SYS_ERR
> handling in mhi_async_power_up(). Once the host detects that the device
> is in SYS_ERR state, it issues MHI_RESET and waits for the device to
> process the reset request. During this time, the device triggers 
> SYS_ERR
> interrupt to the host and host starts handling SYS_ERR execution.
> 
> So by the time the device has completed reset, host starts SYS_ERR
> handling. This causes the race condition and the modem fails to boot.
> 
> Hence, register the IRQ handler only after handling the SYS_ERR check
> to avoid getting spurious IRQs from the device.
> 
> Cc: stable@vger.kernel.org
> Fixes: e18d4e9fa79b ("bus: mhi: core: Handle syserr during power_up")
> Reported-by: Aleksander Morgado <aleksander@aleksander.es>
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
> ---
> 
> Changes in v2:
> 
> * Switched to "mhi_poll_reg_field" for detecting MHI reset in device.
> 
>  drivers/bus/mhi/core/pm.c | 32 ++++++++++----------------------
>  1 file changed, 10 insertions(+), 22 deletions(-)
> 
> diff --git a/drivers/bus/mhi/core/pm.c b/drivers/bus/mhi/core/pm.c
> index fb99e3727155..3c347fe9b10d 100644
> --- a/drivers/bus/mhi/core/pm.c
> +++ b/drivers/bus/mhi/core/pm.c
> @@ -1038,7 +1038,6 @@ int mhi_async_power_up(struct mhi_controller 
> *mhi_cntrl)
>  	enum mhi_ee_type current_ee;
>  	enum dev_st_transition next_state;
>  	struct device *dev = &mhi_cntrl->mhi_dev->dev;
> -	u32 val;
u32 interval_us = 25000; /* poll register field every 25 milliseconds */
>  	int ret;
> 
>  	dev_info(dev, "Requested to power ON\n");
> @@ -1055,10 +1054,6 @@ int mhi_async_power_up(struct mhi_controller 
> *mhi_cntrl)
>  	mutex_lock(&mhi_cntrl->pm_mutex);
>  	mhi_cntrl->pm_state = MHI_PM_DISABLE;
> 
> -	ret = mhi_init_irq_setup(mhi_cntrl);
> -	if (ret)
> -		goto error_setup_irq;
> -
>  	/* Setup BHI INTVEC */
>  	write_lock_irq(&mhi_cntrl->pm_lock);
>  	mhi_write_reg(mhi_cntrl, mhi_cntrl->bhi, BHI_INTVEC, 0);
Let's also set the BHI INTVEC up _after_ the IRQ setup is done. I 
believe doing
this before setting up IRQs may be racy.
> @@ -1072,7 +1067,7 @@ int mhi_async_power_up(struct mhi_controller 
> *mhi_cntrl)
>  		dev_err(dev, "%s is not a valid EE for power on\n",
>  			TO_MHI_EXEC_STR(current_ee));
>  		ret = -EIO;
> -		goto error_async_power_up;
> +		goto error_setup_irq;
>  	}
> 
>  	state = mhi_get_mhi_state(mhi_cntrl);
> @@ -1081,20 +1076,12 @@ int mhi_async_power_up(struct mhi_controller 
> *mhi_cntrl)
> 
>  	if (state == MHI_STATE_SYS_ERR) {
>  		mhi_set_mhi_state(mhi_cntrl, MHI_STATE_RESET);
> -		ret = wait_event_timeout(mhi_cntrl->state_event,
> -				MHI_PM_IN_FATAL_STATE(mhi_cntrl->pm_state) ||
> -					mhi_read_reg_field(mhi_cntrl,
> -							   mhi_cntrl->regs,
> -							   MHICTRL,
> -							   MHICTRL_RESET_MASK,
> -							   MHICTRL_RESET_SHIFT,
> -							   &val) ||
> -					!val,
> -				msecs_to_jiffies(mhi_cntrl->timeout_ms));
> -		if (!ret) {
> -			ret = -EIO;
> +		ret = mhi_poll_reg_field(mhi_cntrl, mhi_cntrl->regs, MHICTRL,
> +				 MHICTRL_RESET_MASK, MHICTRL_RESET_SHIFT, 0,
> +				 msecs_to_jiffies(mhi_cntrl->timeout_ms));
Use "interval_us" as the last argument here since this API takes the 
polling interval
value in microseconds as the last argument.
> +		if (ret) {
>  			dev_info(dev, "Failed to reset MHI due to syserr state\n");
> -			goto error_async_power_up;
> +			goto error_setup_irq;
>  		}
> 
>  		/*
> @@ -1104,6 +1091,10 @@ int mhi_async_power_up(struct mhi_controller 
> *mhi_cntrl)
>  		mhi_write_reg(mhi_cntrl, mhi_cntrl->bhi, BHI_INTVEC, 0);
>  	}
> 
> +	ret = mhi_init_irq_setup(mhi_cntrl);
> +	if (ret)
> +		goto error_setup_irq;
> +
>  	/* Transition to next state */
>  	next_state = MHI_IN_PBL(current_ee) ?
>  		DEV_ST_TRANSITION_PBL : DEV_ST_TRANSITION_READY;
> @@ -1116,9 +1107,6 @@ int mhi_async_power_up(struct mhi_controller 
> *mhi_cntrl)
> 
>  	return 0;
> 
> -error_async_power_up:
> -	mhi_deinit_free_irq(mhi_cntrl);
> -
>  error_setup_irq:
>  	mhi_cntrl->pm_state = MHI_PM_DISABLE;
>  	mutex_unlock(&mhi_cntrl->pm_mutex);

Thanks,
Bhaumik
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