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Date:   Wed, 16 Jan 2019 11:53:50 +0100
From:   Thomas Petazzoni <thomas.petazzoni@bootlin.com>
To:     Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Cc:     linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org,
        Peter Chen <Peter.Chen@nxp.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Subject: Re: [PATCH] usb: chipidea: Grab the (legacy) USB PHY by phandle
 first
Message-ID: <20190116115350.3daa9b4f@windsurf>
In-Reply-To: <20190116101051.21202-1-paul.kocialkowski@bootlin.com>
References: <20190116101051.21202-1-paul.kocialkowski@bootlin.com>
Organization: Bootlin
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Sender: linux-kernel-owner@vger.kernel.org
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Hello,

Thanks for the patch!

On Wed, 16 Jan 2019 11:10:51 +0100, Paul Kocialkowski wrote:
> According to the chipidea driver bindings, the USB PHY is specified via
> the "phys" phandle node. However, this only takes effect for USB PHYs
> that use the common PHY framework. For legacy USB PHYs, a simple lookup
> based on the USB PHY type is done instead.
> 
> This does not play out well when more than USB PHY is registered, since

"more than *one*"

> the first registered PHY matching the type will always be returned
> regardless of what the driver was bound to.
> 
> Fix this by looking up the PHY based on the "phys" phandle node.
> Although generic PHYS and rather matched by their "phys-name"

I'm confused by "Although generic PHYS and rather matched". Perhaps
s/and/are/ ?

Also PHYS -> PHYs

> and not
> the "phys" phandle directly, there is no helper for similar lookup on
> legacy PHYs and it's probably not worth the effort to add it.
> 
> When no legacy USB PHY is found by phandle, fallback to grabbing any
> registered USB2 PHY. This ensures backward compatibility if some users
> were actually relying on this mechanism.
> 
> Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
> ---
>  drivers/usb/chipidea/core.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/chipidea/core.c b/drivers/usb/chipidea/core.c
> index 7bfcbb23c2a4..11d3ee1e3fe5 100644
> --- a/drivers/usb/chipidea/core.c
> +++ b/drivers/usb/chipidea/core.c
> @@ -954,8 +954,14 @@ static int ci_hdrc_probe(struct platform_device *pdev)
>  	} else if (ci->platdata->usb_phy) {
>  		ci->usb_phy = ci->platdata->usb_phy;
>  	} else {
> +		ci->usb_phy = devm_usb_get_phy_by_phandle(dev->parent, "phys",
> +							  0);
>  		ci->phy = devm_phy_get(dev->parent, "usb-phy");
> -		ci->usb_phy = devm_usb_get_phy(dev->parent, USB_PHY_TYPE_USB2);

I'm not sure why you change the order of legacy PHY lookup vs. generic
PHY lookup.

> +
> +		/* Fallback to grabbing any registered USB2 PHY */
> +		if (IS_ERR(ci->phy) && IS_ERR(ci->usb_phy))
> +			ci->usb_phy = devm_usb_get_phy(dev->parent,
> +						       USB_PHY_TYPE_USB2);

Why is this conditional on the generic PHY lookup failing?

Don't we simply want:

	ci->phy = devm_phy_get(dev->parent, "usb-phy");
	ci->usb_phy = devm_usb_get_phy_by_phandle(dev->parent, "phys", 0);
	if (IS_ERR(ci->usb_phy))
		ci->usb_phy = devm_usb_get_phy(dev->parent, USB_PHY_TYPE_USB2);

 ?

Does this needs a "Fixes:" tag ? It's not fixing a regression because
nobody complained until now, but it's really fixing a behavior that
wasn't correct.

Best regards,

Thomas
-- 
Thomas Petazzoni, CTO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com