linux-kernel - Re: [PATCH v3] usb: typec: get the vbus source and charge values from the devicetree

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Message-ID: <20180912163259.GC3300@roeck-us.net>
Date:   Wed, 12 Sep 2018 09:32:59 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Angus Ainslie <angus@...ea.ca>
Cc:     Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] usb: typec: get the vbus source and charge values
 from  the devicetree

On Wed, Sep 12, 2018 at 10:08:58AM -0600, Angus Ainslie wrote:
> On 2018-09-11 09:33, Guenter Roeck wrote:
> >I cant put my finger on it but this seems wrong. As i said both src
> >and sink should never be true at the same time. I also din’t
> >understand why turning off src should power off your board. Ultimately
> >my concern is that we may be just painting over the real problem, and
> >that would be really bad to do with dt properties.
> >
> 
> I agree that this doesn't seem like the correct way of solving the problem.
> On this HW (Emcraft iMX8M BSB) I think the PTN5110 chip has been connected
> correctly so I'm assuming that it is some quirk of the PTN5110.
> 
> I didn't design the HW or the chip. This is a workaround for "quirky"
> hardware and there may be others that don't behave exactly as expected.
> 

I wouldn't be that sure about that. It may as well be that the tcpc driver
and/or the tcpm driver are doing something wrong when initializing.

I didn't really understand the logs you sent out earlier. It looked like
the system would loose power if the TCPC_CMD_DISABLE_SRC_VBUS command is
sent.  That doesn't really make sense to me since it indicates that the
chip sources power to the remote, and turning that off should not result
in a local loss of power.

Note that the chip is supposed to be able to report if it is sourcing vbus
and if VBUS is present, in the POWER_STATUS register. Another question is
the content of the ROLE_CONTROL register when the system boots, and the
DEVICE_CAPABILITIES settings.

Overall I suspect that we don't handle startup for your system correctly
in the tcpc driver. The ideal solution would be to find a solution which
does not require any devicetree properties, but to do that we'll need
to get a better understanding about your system's requirements.

Guenter