On Wed, Mar 10, 2021 at 01:41:58PM -0700, Jeffrey Hugo wrote:
> After the device has signaled the end of reset by clearing the reset bit,
> it will automatically reinit MHI and the internal device structures. Once
> That is done, the device will signal it has entered the ready state.
>
> Signaling the ready state involves sending an interrupt (MSI) to the host
> which might cause IOMMU faults if it occurs at the wrong time.
>
> If the controller is being powered down, and possibly removed, then the
> reset flow would only wait for the end of reset. At which point, the host
> and device would start a race. The host may complete its reset work, and
> remove the interrupt handler, which would cause the interrupt to be
> disabled in the IOMMU. If that occurs before the device signals the ready
> state, then the IOMMU will fault since it blocked an interrupt. While
> harmless, the fault would appear like a serious issue has occurred so let's
> silence it by making sure the device hits the ready state before the host
> completes its reset processing.
>
> Signed-off-by: Jeffrey Hugo <jh...@codeaurora.org>
> ---
> drivers/bus/mhi/core/pm.c | 17 ++++++++++++++++-
> 1 file changed, 16 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/bus/mhi/core/pm.c b/drivers/bus/mhi/core/pm.c
> index adb0e80..414da4f 100644
> --- a/drivers/bus/mhi/core/pm.c
> +++ b/drivers/bus/mhi/core/pm.c
> @@ -467,7 +467,7 @@ 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;
> + u32 in_reset = -1, ready = 0;
> unsigned long timeout = msecs_to_jiffies(mhi_cntrl->timeout_ms);
>
> dev_dbg(dev, "Triggering MHI Reset in device\n");
> @@ -490,6 +490,21 @@ static void mhi_pm_disable_transition(struct
> mhi_controller *mhi_cntrl)
> * hence re-program it
> */
> mhi_write_reg(mhi_cntrl, mhi_cntrl->bhi, BHI_INTVEC, 0);
> +
> + if (!MHI_IN_PBL(mhi_get_exec_env(mhi_cntrl))) {
> + /* wait for ready to be set */
> + ret = wait_event_timeout(mhi_cntrl->state_event,
> + mhi_read_reg_field(mhi_cntrl,
> + mhi_cntrl->regs,
> + MHISTATUS,
> + MHISTATUS_READY_MASK,
> + MHISTATUS_READY_SHIFT,
> + &ready)
> + || ready, timeout);
> + if (!ret || !ready)
> + dev_warn(dev,
> + "Device failed to enter READY state\n");
Wouldn't dev_err be more appropriate here provided that we might get IOMMU fault
anytime soon?
Thanks,
Mani
> + }
> }
>
> dev_dbg(dev,
> --
> Qualcomm Technologies, Inc. is a member of the
> Code Aurora Forum, a Linux Foundation Collaborative Project.
>
