Re: [PATCH v2] bus: mhi: core: Fix power down latency

[Manivannan Sadhasivam <mani@kernel.org>]

On Mon, May 03, 2021 at 10:04:50AM +0200, Loic Poulain wrote:
> On graceful power-down/disable transition, when an MHI reset is
> performed, the MHI device loses its context, including interrupt
> configuration. However, the current implementation is waiting for
> event(irq) driven state change to confirm reset has been completed,
> which never happens, and causes reset timeout, leading to unexpected
> high latency of the mhi_power_down procedure (up to 45 seconds).
> 
> Fix that by moving to the recently introduced poll_reg_field method,
> waiting for the reset bit to be cleared, in the same way as the
> power_on procedure.
> 
> Fixes: a6e2e3522f29 ("bus: mhi: core: Add support for PM state transitions")
> Signed-off-by: Loic Poulain <loic.poulain@linaro.org>

Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>

Thanks,
Mani

> ---
>  drivers/bus/mhi/core/pm.c | 18 +++++-------------
>  1 file changed, 5 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/bus/mhi/core/pm.c b/drivers/bus/mhi/core/pm.c
> index e2e59a3..704a5e2 100644
> --- a/drivers/bus/mhi/core/pm.c
> +++ b/drivers/bus/mhi/core/pm.c
> @@ -465,23 +465,15 @@ static void mhi_pm_disable_transition(struct mhi_controller *mhi_cntrl)
>  
>  	/* Trigger MHI RESET so that the device will not access host memory */
>  	if (!MHI_PM_IN_FATAL_STATE(mhi_cntrl->pm_state)) {
> -		u32 in_reset = -1;
> -		unsigned long timeout = msecs_to_jiffies(mhi_cntrl->timeout_ms);
> -
>  		dev_dbg(dev, "Triggering MHI Reset in device\n");
>  		mhi_set_mhi_state(mhi_cntrl, MHI_STATE_RESET);
>  
>  		/* Wait for the reset bit to be cleared by the device */
> -		ret = wait_event_timeout(mhi_cntrl->state_event,
> -					 mhi_read_reg_field(mhi_cntrl,
> -							    mhi_cntrl->regs,
> -							    MHICTRL,
> -							    MHICTRL_RESET_MASK,
> -							    MHICTRL_RESET_SHIFT,
> -							    &in_reset) ||
> -					!in_reset, timeout);
> -		if (!ret || in_reset)
> -			dev_err(dev, "Device failed to exit MHI Reset state\n");
> +		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");
>  
>  		/*
>  		 * Device will clear BHI_INTVEC as a part of RESET processing,
> -- 
> 2.7.4
>