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

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Message-ID: <80b6c87a-001c-96ae-d0ce-f41b48362d80@codeaurora.org>
Date:   Wed, 10 Mar 2021 12:56:59 -0800
From:   Hemant Kumar <hemantk@...eaurora.org>
To:     Jeffrey Hugo <jhugo@...eaurora.org>,
        manivannan.sadhasivam@...aro.org
Cc:     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 3/10/21 12:41 PM, 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>

Reviewed-by: Hemant Kumar <hemantk@...eaurora.org>

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