linux-kernel - RE: [PATCH] usb: chipidea: Grab the (legacy) USB PHY by phandle first

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Message-ID: <VI1PR04MB5327613BC3BE3F579017E6EE8B9C0@VI1PR04MB5327.eurprd04.prod.outlook.com>
Date:   Fri, 18 Jan 2019 02:18:59 +0000
From:   Peter Chen <peter.chen@....com>
To:     Paul Kocialkowski <paul.kocialkowski@...tlin.com>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>
CC:     "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: RE: [PATCH] usb: chipidea: Grab the (legacy) USB PHY by phandle first

 
> On Thu, 2019-01-17 at 06:44 +0000, Peter Chen wrote:
> >
> > > On Wed, 2019-01-16 at 14:44 +0100, Thomas Petazzoni wrote:
> > > > Well prior to your code, there was already a possibility for both
> > > > ci->phy and ci->usb_phy to be valid. I don't think it's really
> > > > ci->useful
> > > > to avoid the fallback when a generic PHY has already been found,
> > > > it's confusing. If really you want to clarify that, it should be:
> > > >
> > > > 	/* Let's first try to find a generic PHY */
> > > > 	ci->phy = devm_phy_get(dev->parent, "usb-phy");
> > > > 	if (IS_ERR(ci->phy)) {
> >
> > Please consider -EPROBE_DEFER case
> >
> > > > 		/* Fall back to legacy USB PHY */
> > > > 		ci->usb_phy = devm_usb_get_phy_by_phandle(dev->parent, "phys",
> > > 0);
> >
> > Please consider -EPROBE_DEFER case
> >
> > > > 		if (IS_ERR(ci->usb_phy))
> > > > 			ci->usb_phy = devm_usb_get_phy(dev->parent,
> > > USB_PHY_TYPE_USB2);
> > > > 	}
> > > >
> >
> > Below code
> >                 if (IS_ERR(ci->phy) && IS_ERR(ci->usb_phy)) {
> >                         ret = -EPROBE_DEFER;
> >                         goto ulpi_exit;
> >                 }
> >
> > needs to change as:
> >
> >                 if (PTR_ERR(ci->phy) ==-EPROBE_DEFER  ||  PTR_ERR(ci->usb_phy)
> == -EPROBE_DEFER) {
> >                         ret = -EPROBE_DEFER;
> >                         goto ulpi_exit;
> >                 }
> 
> Well I think this was more of a general outline than proper code to be included in
> the driver anyway :)
> 
> I'm rather considering implementing what Thomas suggested at first, which is going
> for the fallback even if a generic PHY was found, as to stick more closely to the
> existing behavior.
> 

Since one USB2 controller is impossible has two USB PHYs, if both PHYs (generic PHY
and USB PHY) are found, there must be error at code or dts. Besides, -EPROBE_DEFER
is not an real error, it means the PHY(USB-PHY) is existed, just not be ready.

Peter

> Cheers,
> 
> Paul
> 
> > Peter
> >
> > > > With that, you would only have either ci->phy or ci->usb_phy be
> > > > valid, and never both. With  your change, you can have ci->phy and
> > > > ci->usb_phy both be valid if the legacy USB PHY was found using
> > > > devm_usb_get_phy_by_phandle(), but not if we fell back to
> > > > devm_usb_get_phy().
> > >
> > > Okay that makes sense, your suggestion is indeed more consistent
> > > with the existing behavior. I'll go with that in the next revision!
> > >
> >
> >
> --
> Paul Kocialkowski, Bootlin
> Embedded Linux and kernel engineering
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