Re: [PATCH v2 3/3] Revert "usb: common: usb-conn-gpio: Make VBUS supply optional"

From: Chunfeng Yun <chunfeng.yun@mediatek.com>
To: Thierry Reding <treding@nvidia.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Liam Girdwood <lgirdwood@gmail.com>,
	Mark Brown <broonie@kernel.org>,
	Matthias Brugger <matthias.bgg@gmail.com>,
	Paul Cercueil <paul@crapouillou.net>,
	Lee Jones <lee.jones@linaro.org>, <linux-usb@vger.kernel.org>,
	<linux-kernel@vger.kernel.org>,
	<linux-arm-kernel@lists.infradead.org>,
	<linux-mediatek@lists.infradead.org>
Subject: Re: [PATCH v2 3/3] Revert "usb: common: usb-conn-gpio: Make VBUS supply optional"
Date: Mon, 24 May 2021 13:51:51 +0800	[thread overview]
Message-ID: <1621835511.26501.14.camel@mhfsdcap03> (raw)
In-Reply-To: <YKezl0nlWFQhLyf/@orome.fritz.box>

On Fri, 2021-05-21 at 15:20 +0200, Thierry Reding wrote:
> On Wed, May 19, 2021 at 02:39:46PM +0800, Chunfeng Yun wrote:
> > Vbus is already an optional supply, if the vbus-supply is not
> > provided in DTS, will use a dummy regulator,
> 
> That statement is not entirely correct. The dummy regulator is
> substituted only if the supply is in fact not optional. The idea behind
> that is to allow DTS files that don't specify all required regulators to
> get away with it, based on the assumption that the supply is one of
> those always-on supplies that are often not described in DTS.
Yes, you are right.
But from the point of result, it indeed can help to handle the absent
regulator.
> 
> > the warning log is as below:
> > "supply vbus not found, using dummy regulator"
> 
> And the reason why we get that warning is to point out that the DTS has
> a bug and that it should be fixed (by adding a proper regulator to take
> the place of the dummy).
> 
> > This reverts commit 4ddf1ac79e5f082451cd549283d2eb7559ab6ca9.
> 
> But if you read the description of that commit, the purpose of that
> patch was in fact to make the supply completely optional in the case
> where we already have the VBUS supply specified for the USB port that
> the connector is parented to.
Could you please give an example you mentioned?

It seems prefer to provide vbus supply in connector instead of port
according to dt-binding

Thanks

> 
> So in that case the DTS doesn't have the bug because the VBUS supply is
> already specified for the USB port and therefore it doesn't have to be
> specified in the USB connector again. In fact, specifying it twice can
> lead to a situation where the USB port may not be able to switch the
> VBUS supply on or off because the setting might conflict with that of
> the USB connector.

> 
> So unless there's a real reason why this is needed, I don't think this
> should be applied.
> 
> Thierry
> 
> > Cc: Thierry Reding <treding@nvidia.com>
> > Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
> > ---
> > v2: remove unused variable "need_vbus"
> > ---
> >  drivers/usb/common/usb-conn-gpio.c | 30 ++++++------------------------
> >  1 file changed, 6 insertions(+), 24 deletions(-)
> > 
> > diff --git a/drivers/usb/common/usb-conn-gpio.c b/drivers/usb/common/usb-conn-gpio.c
> > index dfbbc4f51ed6..65d89140cd19 100644
> > --- a/drivers/usb/common/usb-conn-gpio.c
> > +++ b/drivers/usb/common/usb-conn-gpio.c
> > @@ -91,14 +91,14 @@ static void usb_conn_detect_cable(struct work_struct *work)
> >  		return;
> >  	}
> >  
> > -	if (info->last_role == USB_ROLE_HOST && info->vbus)
> > +	if (info->last_role == USB_ROLE_HOST)
> >  		regulator_disable(info->vbus);
> >  
> >  	ret = usb_role_switch_set_role(info->role_sw, role);
> >  	if (ret)
> >  		dev_err(info->dev, "failed to set role: %d\n", ret);
> >  
> > -	if (role == USB_ROLE_HOST && info->vbus) {
> > +	if (role == USB_ROLE_HOST) {
> >  		ret = regulator_enable(info->vbus);
> >  		if (ret)
> >  			dev_err(info->dev, "enable vbus regulator failed\n");
> > @@ -106,9 +106,8 @@ static void usb_conn_detect_cable(struct work_struct *work)
> >  
> >  	info->last_role = role;
> >  
> > -	if (info->vbus)
> > -		dev_dbg(info->dev, "vbus regulator is %s\n",
> > -			regulator_is_enabled(info->vbus) ? "enabled" : "disabled");
> > +	dev_dbg(info->dev, "vbus regulator is %s\n",
> > +		regulator_is_enabled(info->vbus) ? "enabled" : "disabled");
> >  
> >  	power_supply_changed(info->charger);
> >  }
> > @@ -175,7 +174,6 @@ static int usb_conn_probe(struct platform_device *pdev)
> >  {
> >  	struct device *dev = &pdev->dev;
> >  	struct usb_conn_info *info;
> > -	bool need_vbus = true;
> >  	int ret = 0;
> >  
> >  	info = devm_kzalloc(dev, sizeof(*info), GFP_KERNEL);
> > @@ -205,23 +203,7 @@ static int usb_conn_probe(struct platform_device *pdev)
> >  
> >  	INIT_DELAYED_WORK(&info->dw_det, usb_conn_detect_cable);
> >  
> > -	/*
> > -	 * If the USB connector is a child of a USB port and that port already provides the VBUS
> > -	 * supply, there's no need for the USB connector to provide it again.
> > -	 */
> > -	if (dev->parent && dev->parent->of_node) {
> > -		if (of_find_property(dev->parent->of_node, "vbus-supply", NULL))
> > -			need_vbus = false;
> > -	}
> > -
> > -	if (!need_vbus) {
> > -		info->vbus = devm_regulator_get_optional(dev, "vbus");
> > -		if (PTR_ERR(info->vbus) == -ENODEV)
> > -			info->vbus = NULL;
> > -	} else {
> > -		info->vbus = devm_regulator_get(dev, "vbus");
> > -	}
> > -
> > +	info->vbus = devm_regulator_get(dev, "vbus");
> >  	if (IS_ERR(info->vbus)) {
> >  		ret = PTR_ERR(info->vbus);
> >  		return dev_err_probe(dev, ret, "failed to get vbus :%d\n", ret);
> > @@ -288,7 +270,7 @@ static int usb_conn_remove(struct platform_device *pdev)
> >  
> >  	cancel_delayed_work_sync(&info->dw_det);
> >  
> > -	if (info->last_role == USB_ROLE_HOST && info->vbus)
> > +	if (info->last_role == USB_ROLE_HOST)
> >  		regulator_disable(info->vbus);
> >  
> >  	usb_role_switch_put(info->role_sw);
> > -- 
> > 2.18.0
> >