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

[Bhaumik Bhatt <bbhatt@codeaurora.org>]

On 2021-04-28 01:29 AM, Loic Poulain wrote:
> On gracefull power-down/disable transition, a MHI reset is performed,
On _graceful_ power-down/disable transition, _when an_ MHI reset is 
performed,
> the MHI device then looses its context, including interrupt config.
the MHI device _loses_ its context, including interrupt configuration.
> However the current implementation is waiting for event(irq) driven
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.
> 
> 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.
> 
> Signed-off-by: Loic Poulain <loic.poulain@linaro.org>
> ---
>  drivers/bus/mhi/core/pm.c | 17 +++++------------
>  1 file changed, 5 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/bus/mhi/core/pm.c b/drivers/bus/mhi/core/pm.c
> index e2e59a3..9c61d3f 100644
> --- a/drivers/bus/mhi/core/pm.c
> +++ b/drivers/bus/mhi/core/pm.c
> @@ -3,7 +3,6 @@
>   * Copyright (c) 2018-2020, The Linux Foundation. All rights reserved.
>   *
>   */
> -
>  #include <linux/delay.h>
>  #include <linux/device.h>
>  #include <linux/dma-direction.h>
> @@ -471,17 +470,11 @@ static void mhi_pm_disable_transition(struct
> mhi_controller *mhi_cntrl)
>  		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,

Thanks,
Bhaumik
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