linux-kernel - Re: [PATCH v2 RESEND] bus: mhi: core: Wait for ready state after reset

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Message-ID: <20210316061433.GG1798@thinkpad>
Date:   Tue, 16 Mar 2021 11:44:33 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     Jeffrey Hugo <jhugo@...eaurora.org>
Cc:     hemantk@...eaurora.org, bbhatt@...eaurora.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 RESEND] bus: mhi: core: Wait for ready state after
 reset

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 <jhugo@...eaurora.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.
>