linux-kernel - Re: [PATCH v3] bus: mhi: host: Wait for ready state after reset

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Message-ID: <20220418141248.GC161722@thinkpad>
Date:   Mon, 18 Apr 2022 19:42:48 +0530
From:   Manivannan Sadhasivam <mani@...nel.org>
To:     Jeffrey Hugo <quic_jhugo@...cinc.com>
Cc:     quic_hemantk@...cinc.com, quic_bbhatt@...cinc.com,
        mhi@...ts.linux.dev, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] bus: mhi: host: Wait for ready state after reset

On Mon, Apr 18, 2022 at 07:53:24AM -0600, Jeffrey Hugo wrote:
> On 4/18/2022 12:26 AM, Manivannan Sadhasivam wrote:
> > On Wed, Apr 13, 2022 at 12:52:26PM -0600, Jeffrey Hugo wrote:
> > > From: Jeffrey Hugo <jhugo@...eaurora.org>
> > > 
> > > 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>
> > > Signed-off-by: Jeffrey Hugo <quic_jhugo@...cinc.com>
> > 
> > I was about to apply this patch but wanted to check with you on using the
> > double signed-off by tags. If the patch get's handed over between multiple
> > developers then multiple signed-off by's make sense. But since it is you that
> > handled the earlier patch also, I think one tag is enough with your new domain.
> > 
> > One more thing is, using codeaurora domain will bounce now. So, please use the
> > quicinc domain for Hemant also.
> 
> I'm aware of the bouncing.  Git send-email however is not, and its default
> behavior can be a bit annoying in this edge case.
> 
> I've seen the dual SoB by the same developer elsewhere in the community, but
> if you want things "cleaned up" to the new quic ids, I'll do that.

Double s-o-b's are common but in this case you handled the patch all the way and
you are still employed by the same employer. Only thing that changed is your
domain, so this makes me feel that single s-o-b is enough.

Thanks,
Mani