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Date:   Wed, 16 Dec 2020 17:59:35 +0100
From:   Jules Maselbas <jmaselbas@...ray.eu>
To:     Minas Harutyunyan <hminas@...opsys.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jules Maselbas <jmaselbas@...ray.eu>
Subject: [RFC PATCH] usb: dwc2: Try usb_get_phy_by_phandle instead of usb_get_phy

On probe the dwc2 driver tries two path to get an usb phy, first calling
devm_phy_get() and secondly with devm_usb_get_phy().

However the current implementation of devm_phy_get() never return a valid
phy for usb-nop-xceiv. And the current implementation of devm_usb_get_phy
only check for phy that's has already been registered.

During boot, I see the dwc2 driver being probed before the usb-nop-xceiv
probe, this means that during the dwc2 probe the function devm_usb_get_phy
never finds the a phy (because it hasn't been registered yet) but never
cause the dwc2 probe to defer.

I tried to follow what is done by dwc3_core_get_phy(): if the current
device has an of_node then try to get the usb_phy by phandle instead of
using devm_usb_get_phy(). This way when the probe order is not good the
devm_usb_get_phy_by_phandle() function will return -EPROBE_DEFER.

Signed-off-by: Jules Maselbas <jmaselbas@...ray.eu>
--- 8< ---

A snippet of the device-tree source I am using:
        &usb0 {
                phys = <&usb_phy0>;
                phy-names = "usb2-phy";
        };
        &usb_phy0 {
                #phy-cells = <0>;
                compatible = "usb-nop-xceiv";
                reset-gpios = <&gpio 0 GPIO_ACTIVE_LOW>;
        };
---
 drivers/usb/dwc2/platform.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/dwc2/platform.c b/drivers/usb/dwc2/platform.c
index db9fd4bd1a38..b58ce996add7 100644
--- a/drivers/usb/dwc2/platform.c
+++ b/drivers/usb/dwc2/platform.c
@@ -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");
+		if (hsotg->dev->of_node && i >= 0)
+			hsotg->uphy = devm_usb_get_phy_by_phandle(hsotg->dev, "phys", i);
+		else
+			hsotg->uphy = devm_usb_get_phy(hsotg->dev, USB_PHY_TYPE_USB2);
 		if (IS_ERR(hsotg->uphy)) {
 			ret = PTR_ERR(hsotg->uphy);
 			switch (ret) {
-- 
2.17.1


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