linux-kernel - Re: [PATCH] usb: phy: Restore deferred probing path

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Message-ID: <54806325.4060306@cogentembedded.com>
Date:	Thu, 04 Dec 2014 16:35:33 +0300
From:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:	Thierry Reding <thierry.reding@...il.com>
CC:	Felipe Balbi <balbi@...com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usb: phy: Restore deferred probing path

On 12/4/2014 4:22 PM, Thierry Reding wrote:

>>> From: Thierry Reding <treding@...dia.com>

>>> Commit 1290a958d48e ("usb: phy: propagate __of_usb_find_phy()'s error on
>>> failure") broke platforms that rely on deferred probing to order probing
>>> of PHY and host controller drivers. The reason is that the commit simply
>>> propagates errors from __of_usb_find_phy(), which returns -ENODEV if no
>>> PHY has been registered yet for a given device tree node. The only case
>>> in which -EPROBE_DEFER would now be returned is if try_module_get() did
>>> fail, which does not make sense.

>>> The correct thing to do is to return -EPROBE_DEFER if a PHY hasn't been
>>> registered yet. The only condition under which it makes sense to return
>>> -ENODEV is if the device tree node representing the PHY has been
>>> disabled (via the status property) because in that case the PHY will
>>> never be registered.

>>> This patch addresses the problem by making __of_usb_find_phy() return an
>>> appropriate error code while keeping in line with the above-mentioned
>>> commit to propagate error codes rather than overwriting them. At the
>>> same time the check for a valid PHY is decoupled from the check for the
>>> try_module_get() call and a separate error code is returned if the
>>> latter fails.

>>> Signed-off-by: Thierry Reding <treding@...dia.com>
>>> ---
>>>   drivers/usb/phy/phy.c | 14 ++++++++++----
>>>   1 file changed, 10 insertions(+), 4 deletions(-)

>>> diff --git a/drivers/usb/phy/phy.c b/drivers/usb/phy/phy.c
>>> index b4066a001ba0..2f9735b35338 100644
>>> --- a/drivers/usb/phy/phy.c
>>> +++ b/drivers/usb/phy/phy.c
>> [...]
>>> @@ -190,10 +193,13 @@ struct usb_phy *devm_usb_get_phy_by_phandle(struct device *dev,
>>>   	spin_lock_irqsave(&phy_lock, flags);
>>>
>>>   	phy = __of_usb_find_phy(node);
>>> -	if (IS_ERR(phy) || !try_module_get(phy->dev->driver->owner)) {
>>> -		if (!IS_ERR(phy))
>>> -			phy = ERR_PTR(-EPROBE_DEFER);
>>> +	if (IS_ERR(phy)) {
>>> +		devres_free(ptr);
>>> +		goto err1;
>>> +	}
>>>
>>> +	if (!try_module_get(phy->dev->driver->owner)) {
>>> +		phy = ERR_PTR(-ENODEV);
>>>   		devres_free(ptr);
>>>   		goto err1;
>>>   	}

>>     I think devres_free() should now be called in one place, under the new
>> 'err2' label.

> That'd make things very confusing, though. devres_free() should only be
> called on error, whereas both err1 and err0 are shared with the success
> case as well. If we were to do what you suggest we'd end up with
> something like this:

[...]

> That's pretty spaghetti-like.

    Oh, sorry, I wasn't looking attentively enough. :-/

> Thierry

WBR, Sergei

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