Re: [PATCH v2 05/22] doc: dt-binding: usb: add otg related properties

[Peter Chen <peter.chen-KZfg59tc24xl57MIdRCFDg@public.gmane.org>]

On Tue, Jun 09, 2015 at 06:29:31PM +0300, Roger Quadros wrote:
> Rob,
> 
> On Tue, 9 Jun 2015 08:26:20 -0500
> Rob Herring <robherring2-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> 
> > On Mon, Jun 8, 2015 at 8:18 PM, Li Jun <b47624-KZfg59tc24xl57MIdRCFDg@public.gmane.org> wrote:
> > > On Mon, Jun 08, 2015 at 11:06:49AM -0500, Rob Herring wrote:
> > >> On Mon, Jun 8, 2015 at 10:02 AM, Li Jun <jun.li-KZfg59tc24xl57MIdRCFDg@public.gmane.org> wrote:
> > >> > Add otg version, srp, hnp and adp support for usb OTG port, then those OTG
> > >> > features don't have to be decided by usb gadget drivers.
> > >> >
> > >> > Signed-off-by: Li Jun <jun.li-KZfg59tc24xl57MIdRCFDg@public.gmane.org>
> > >> > ---
> > >> >  Documentation/devicetree/bindings/usb/generic.txt | 10 ++++++++++
> > >> >  1 file changed, 10 insertions(+)
> > >> >
> > >> > diff --git a/Documentation/devicetree/bindings/usb/generic.txt b/Documentation/devicetree/bindings/usb/generic.txt
> > >> > index 477d5bb..7386f4a 100644
> > >> > --- a/Documentation/devicetree/bindings/usb/generic.txt
> > >> > +++ b/Documentation/devicetree/bindings/usb/generic.txt
> > >> > @@ -11,6 +11,12 @@ Optional properties:
> > >> >                         "peripheral" and "otg". In case this attribute isn't
> > >> >                         passed via DT, USB DRD controllers should default to
> > >> >                         OTG.
> > >> > + - otg-rev: tells usb driver the release number of the OTG and EH supplement
> > >> > +                       with which the device and its descriptors are compliant,
> > >> > +                       in binary-coded decimal (i.e. 2.0 is 0200H).
> > >>
> > >> I would assume OTG 2.0 is somehow backwards compatible? Is this a h/w
> > >> dependency or a driver feature?
> > >>
> > > Not fully compatible, OTG 2.0 extend the usb_otg_descriptor by adding a new
> > > member bcdOTG to identify the OTG version, this descriptor needs to be sent
> > > to OTG host with correct size and content, so we have to know which release
> > > version the OTG device is compliant with, either by menuconfig config or pass
> > > via DT.
> > 
> > So you have to change the version depending on the host you are
> > connected to? That really seems strange that plugging in a OTG 2.0
> > device to an OTG 1.3 host would not work and doesn't make for a good
> > user experience.
> 
> No. The OTG version in the OTG descriptor for any device is usually fixed for the
> lifetime of the product.
> 
> Let's assume it is 2.0.
> 
> If you plug this to OTG 1.0 host, it won't be an issue as OTG 1.0 host doesn't
> read the BCD version.
> 
> > 
> > >> > + - srp-support: tells OTG controllers we want to enable SRP.
> > >> > + - hnp-support: tells OTG controllers we want to enable HNP.
> > >> > + - adp-support: tells OTG controllers we want to enable ADP.
> > >>
> > >> I've recently run into a problem[1] and found that I have to disable
> > >> OTG in the kernel to get my device to work. Having to turn-off OTG
> > >> seems like the wrong solution, and shifting the problem to DT seems
> > >> wrong too. Why is this not a user configurable option (within whatever
> > >> h/w constraints there are)?
> > > The problem of below link, seems your device is claiming it's a HNP capable
> > > OTG device, but connecting to a non-OTG port of your Host, assume your Host
> > > does have a OTG port, your Host issue a A_ALT_HNP_SUPPORT request to your
> > > OTG device to remind it can use another port with HNP, but the request failed
> > > (maybe STALL by your device, this request is defined in OTG 1.3 but obsolete
> > > in OTG 2.0), so your Host just stopped enumeration of your device, this is not
> > > reasonable because current OTG code is some out of data.
> > 
> > Do PCs have OTG ports typically? My expectation is that if I plug in
> > an OTG device as a B device to any host port, that it will work as a
> > device no matter what the host OTG capabilities are. If I have to
> > change the kernel config or DT, that is a problem.
> 
> AFAIK PCs don't have OTG ports.
> 
> If you plug in OTG device to a non-otg host port it will work as normal B-device.
> The host doesn't request for OTG descriptors and doesn't care what OTG features it
> supports or not.
> 
> > 
> > > I am trying to make those OTG feaures to be configurable options, you mean
> > > by sys?
> > 
> > Yes.
> 
> why do you need OTG features to be sysfs configurable other than for debugging?
> 
> > 
> > >> What are the valid combinations? When do we want these enabled or not?
> > >> Wouldn't default enabled be better?
> > >
> > > We want to enable all those support in kernel driver, but some platform or
> > > hardware may not want to enable any or some of them, so those hardware
> > > can disable it by not pass the property in dt, the 3 sub features of OTG are
> > > not mandatory for so called OTG device, normally we at least enable HNP, and
> > > SRP and ADP are optional.
> > 
> > Please answer my questions in the doc.
> > 
> > >>
> > >> We already have dr_mode property. How is it related to these?
> 
> dr_mode states what mode the controller will operate in.
> 
> for dr_mode == "host" we don't care about these otg flags.
> 
> for dr_mode == "peripheral" or dr_mode == "otg"
> we care about these OTG flags to create our OTG descriptor on the fly.
> 

If dr_mode = "peripheral", we should not create OTG descriptor,
otherwise, the otg device at other side may consider it is an
"otg" device.

Peter
> > >
> > > dr_mode is to tell the device it will work at OTG mode(there is another simple
> > > dual role mode which is commom used but not HNP), srp/hnp/adp can further specify
> > > which protocol the OTG device will support.
> > 
> > By simple DR, you mean ID pin detect, right. So please define how you
> > support just ID pin detect vs. other levels of capability. Does only
> > dr_mode = otg mean ID pin detect? That may be a problem for existing
> > DTs if you disable other OTG functions because they have not been
> > added to the DT, then that is a problem.
> > 
> > I'm feeling less convinced that this belongs in DT at all. Please
> > convince me otherwise.
> 
> Yes not specifying anything in DT should work and default to the
> best OTG version and features supported by the OTG controller.
> 
> But if the device manufacturer wants to restrict the OTG version
> to something less or disable some OTG features then the DT flags come
> into play.
> 
> cheers,
> -roger

-- 

Best Regards,
Peter Chen
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