linux-kernel - Re: [PATCH 0/3] USB: musb: dsps: phy fix and DT-topology support

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Date:   Wed, 18 Apr 2018 20:46:40 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Bin Liu <b-liu@...com>
Cc:     Johan Hovold <johan@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Alan Stern <stern@...land.harvard.edu>,
        Arnd Bergmann <arnd@...db.de>,
        Kishon Vijay Abraham I <kishon@...com>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] USB: musb: dsps: phy fix and DT-topology support

On Wed, Apr 18, 2018 at 11:20:15AM -0500, Bin Liu wrote:
> Johan,
> 
> On Fri, Apr 13, 2018 at 05:15:02PM +0200, Johan Hovold wrote:
> > I've been carrying a patch out-of-tree since my work on improving the
> > USB device-tree support which is needed to be able to describe USB
> > topologies for musb based controllers.
> > 
> > This patch, which associates the platform controller device with the
> > glue device device-tree node, did not play well with the recent changes
> > which added generic phy support to USB core however.
> > 
> > Like the recent dwc2 regression fixed by Arnd after the device-tree
> > #phy-cell changes, the generic phy code in USB core can now also fail
> > indefinitly with -EPROBE_DEFER when the controller uses a legacy USB
> > phy.
> > 
> > The second patch addresses this for musb, which handles its own (legacy
> > and generic) phys, but something more may possibly now be needed for
> > other platforms with legacy phys.
> > 
> > In the process of debugging this, I stumbled over another issue which
> > caused the dsps legacy phy init two be called twice on every probe and
> > which is fixed by the first patch.
> > 
> > Johan
> > 
> > 
> > Johan Hovold (3):
> >   USB: musb: dsps: drop duplicate phy initialisation
> >   USB: musb: host: prevent core phy initialisation
> 
> Are the two bugs only affecting you with your out-of-tree patch? It
> seems don't have any functional impact for me. I need to make a decision
> if these two patches need to go to the stable trees...

The first bug is independent of the third patch (the "out-of-tree"
patch), but as Uwe also noted it seems to be mostly benign since it took
two years for it to be discovered. For that reason, and to minimise the
risk of any stable regressions, I did not mark it for stable.

The second fix is really only needed with the third of_node patch since
I don't think any of the glue drivers propagates the device-tree node in
this way currently. Hence it could also wait for 3.18, and it is in any
case not stable material as the generic-phy support in USB core is new
in 3.17.

Note that other host controllers may have a device-tree node with
associated legacy-phys however and that this could now lead to similar
problems starting with 3.17.

Thanks,
Johan