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

[Loic Poulain <loic.poulain@linaro.org>]

Hi Manivannan and Hemant,

On Mon, 3 May 2021 at 09:55, Loic Poulain <loic.poulain@linaro.org> 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>

Should be considered for 5.13-rc* since it's a fix.

Regards,
Loic

> ---
>  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
>