linux-kernel - Re: [PATCH] usb: typec: ucsi: Clear pending after acking connector change

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Message-ID: <YKT3oEt/9fX8k8mw@kuha.fi.intel.com>
Date:   Wed, 19 May 2021 14:33:52 +0300
From:   Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To:     Benjamin Berg <bberg@...hat.com>
Cc:     Bjorn Andersson <bjorn.andersson@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usb: typec: ucsi: Clear pending after acking connector
 change

On Tue, May 18, 2021 at 08:04:14PM +0200, Benjamin Berg wrote:
> On Tue, 2021-05-18 at 16:29 +0300, Heikki Krogerus wrote:
> > On Mon, May 17, 2021 at 02:57:28PM +0200, Benjamin Berg wrote:
> > > 
> > > [SNIP]
> > > Unfortunately, I don't feel it'll work. The problem that I was
> > > seeing
> > > looked like a race condition in the PPM itself, where the window is
> > > the
> > > time between the UCSI_GET_CONNECTOR_STATUS command and the
> > > subsequent
> > > ACK.
> > > For such a firmware level bug in the PPM, we need a way to detect
> > > the
> > > race condition when it happens (or get a fix for the firmware).
> > 
> > OK. Let me know does the patch bring the issue back for you.
> 
> So, I just tried the patch, and I can occasionally reproduce the issue
> where "online" for the ucsi power adapter is stuck at "1" after
> unplugging with the patch applied.

Thanks for testing it.

I'm still not sure that the PPM is the culprit here. I have a feeling
that the problem you are seeing is caused by the workaround (bad
workaround) that we have for the issue where the EC firmware does not
return with the BUSY bit set in the CCI when it should in many cases.
The UCSI ACPI driver has one minute timeout value for command
completion because of that, which is way too long. So if the EC
firmware decides to take its time before acknowledging command, the
driver is stuck, and we start loosing the events... Well, I guess
technically the PPM would be the culprit in the end in any case, but
I'm just not sure that there is any race like you suspected.

But this is off topic. I'll send you an RFC proposal what I think we
could do about that.

thanks,

-- 
heikki