linux-kernel - Re: [RFC PATCH] usb: dwc2: Try usb_get_phy_by_phandle instead of usb_get

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Message-ID: <20201226134522.fqpsd2fzlri2rcni@tellis.lin.mbt.kalray.eu>
Date:   Sat, 26 Dec 2020 14:45:44 +0100
From:   Jules Maselbas <jmaselbas@...ray.eu>
To:     Artur Petrosyan <Arthur.Petrosyan@...opsys.com>
Cc:     Minas Harutyunyan <Minas.Harutyunyan@...opsys.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] usb: dwc2: Try usb_get_phy_by_phandle instead of
 usb_get_phy

Hi Artur,

On Fri, Dec 25, 2020 at 11:41:04AM +0000, Artur Petrosyan wrote:
> > @@ -251,7 +251,12 @@ static int dwc2_lowlevel_hw_init(struct dwc2_hsotg *hsotg)
> >   	}
> >   
> >   	if (!hsotg->phy) {
> > -		hsotg->uphy = devm_usb_get_phy(hsotg->dev, USB_PHY_TYPE_USB2);
> > +		if (hsotg->dev->of_node)
> > +			i = of_property_match_string(hsotg->dev->of_node, "phy-names", "usb2-phy");
> 
> According the device tree you have provided the value of "i" will always 
> be "0".
Yes

> > +		if (hsotg->dev->of_node && i >= 0)
> > +			hsotg->uphy = devm_usb_get_phy_by_phandle(hsotg->dev, "phys", i);
> 
> Why do you use the value of "i" while in "<&usb_phy0>" you have only one 
> phy. If you had several phy-names and the value of "i" gets more than 0, 
> then based on your usb_phy0 "devm_usb_get_phy_by_phandle" function will 
> return error. So, maybe it would be more correct (based on your device 
> tree), to use below command
> hsotg->uphy = devm_usb_get_phy_by_phandle(hsotg->dev, "phys", 0);
Yes I could use 0 instead of i, but I would like this to work not only
for my case where the "usb2-phy" phandle comes first.

I've tried to follow what's done in phy-core.c, as done by the function
phy_get. Where it first call "of_property_match_string" and then get the
phy with the matched index.

I don't see how, in my case, the function "devm_usb_get_phy_by_phandle" can
be called with i greater than 0, and returning an error.

Best,
Jules