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

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Hi Mani,

On Mon, 8 Nov 2021 at 18:42, Manivannan Sadhasivam
<manivannan.sadhasivam@xxxxxxxxxx> 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@xxxxxxxxxxxxxxx
> Fixes: e18d4e9fa79b ("bus: mhi: core: Handle syserr during power_up")
> Reported-by: Aleksander Morgado <aleksander@xxxxxxxxxxxxx>
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@xxxxxxxxxx>
> ---
>  drivers/bus/mhi/core/pm.c | 26 +++++++++++---------------
>  1 file changed, 11 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/bus/mhi/core/pm.c b/drivers/bus/mhi/core/pm.c
> index fb99e3727155..ec5f11166820 100644
> --- a/drivers/bus/mhi/core/pm.c
> +++ b/drivers/bus/mhi/core/pm.c
> @@ -1055,10 +1055,6 @@ 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);
> @@ -1072,7 +1068,7 @@ 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);
> @@ -1082,19 +1078,18 @@ 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,

Shouldn't we use a polling variant such as mhi_poll_reg_field() given
the interrupts are not yet enabled?

> -                               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,
> +                                        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;
>                         dev_info(dev, "Failed to reset MHI due to syserr state\n");
> -                       goto error_async_power_up;
> +                       goto error_setup_irq;
>                 }

Regards,
Loic



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