Re: [PATCH v5 11/23] usb: chipidea: Emulate OTGSC interrupt enable path

[Peter Chen]

On Tue, Oct 18, 2016 at 06:53:07PM -0700, Stephen Boyd wrote:
> Quoting Peter Chen (2016-10-18 18:15:35)
> > On Mon, Oct 17, 2016 at 06:56:24PM -0700, Stephen Boyd wrote:
> > > In the case of an extcon-usb-gpio device being used with the
> > > chipidea driver we'll sometimes miss the BSVIS event in the OTGSC
> > > register. Consider the case where we don't have a cable attached
> > > and the id pin is indicating "host" mode. When we plug in the usb
> > > cable for "device" mode a gpio goes high and indicates that we
> > > should do the role switch and that vbus is high. When we're in
> > > "host" mode the OTGSC register doesn't have BSVIE set.
> > 
> > I have some questions for your description:
> > 
> > - Do you have any pending or related patches what this patch set
> >   is based on? Afaik, the extcon-usb-gpio has no vbus event supported.
> 
> If you're asking if I've made modifications to extcon-usb-gpio, then the
> answer is no. The branch on linaro.org git server from the cover-letter
> is the branch I've used to test this with. This patch is specifically to
> fix issues with that design on the db410c board that has only one pin
> for ID and vbus detection. It's the schematic that we've discussed in
> another thread.
> 
> extcon-usb-gpio sends two extcon events, EXTCON_USB_HOST (for the id
> pin) and EXTCON_USB (for the vbus). So afaik it does support vbus
> events.
> 

Hmm, in fact, your ID event is the same with vbus event, you take
external vbus event as ID event for extcon-usb-gpio handling. Yes,
it can work due to it sends EXTCON_USB_HOST event first.

Where you change the USB_SW_SEL_PM pin?

> > - When the ID from 0->1, the chipidea driver will do role switch, and
> >   set BSVIE, why it does not occur for your case?
> 
> Right, that happens with this line in the sequence I describe below:
> 
>   hw_write_otgsc(ci, OTGSC_BSVIS | OTGSC_BSVIE, OTGSC_BSVIS | OTGSC_BSVIE);
> 
> but that happens much later than when the extcon event happens so we
> miss the interrupt. Technically, the driver isn't expecting the BSVIS
> interrupt to happen until BSVIE is set, but the extcon can come whenever
> it wants regardless of how the registers are configured in the
> controller.  So we have to do some sort of 'caching' here to remember
> that the vbus event happened and replay it when BSVIE is set. At least I
> imagine this is how the hardware would work? Or if vbus goes high before
> we enable the interrupt would it just be missed? It seems like polling
> the BSV bit and then enabling BSVIE is sort of racy there.
> 
> Plus, we poll the BSV bit when we role switch, but in my case id bit
> toggles and vbus goes high at exactly the same time because that is all
> happening from a single cable being connected, so it's not possible for
> BSV to go low and see it after the id pin from 0 to 1.

Now, I understand your case, but your changes are a little complicated.
Would you try if below patch can fix your issue?