linux-kernel - Re: [PATCH v6 01/12] usb: hcd: Initialize hcd->flags to 0

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Date:	Thu, 7 Apr 2016 13:40:21 +0300
From:	Roger Quadros <rogerq@...com>
To:	Peter Chen <hzpeterchen@...il.com>
CC:	Felipe Balbi <balbi@...nel.org>, <stern@...land.harvard.edu>,
	<gregkh@...uxfoundation.org>, <peter.chen@...escale.com>,
	<dan.j.williams@...el.com>, <jun.li@...escale.com>,
	<mathias.nyman@...ux.intel.com>, <tony@...mide.com>,
	<Joao.Pinto@...opsys.com>, <abrestic@...omium.org>,
	<linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-omap@...r.kernel.org>
Subject: Re: [PATCH v6 01/12] usb: hcd: Initialize hcd->flags to 0

On 07/04/16 12:42, Peter Chen wrote:
> On Wed, Apr 06, 2016 at 09:32:22AM +0300, Roger Quadros wrote:
>> On 06/04/16 09:09, Felipe Balbi wrote:
>>>
>>> Hi,
>>>
>>> Roger Quadros <rogerq@...com> writes:
>>>> diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
>>>> index 2ca2cef..6b1930d 100644
>>>> --- a/drivers/usb/core/hcd.c
>>>> +++ b/drivers/usb/core/hcd.c
>>>> @@ -2706,6 +2706,7 @@ int usb_add_hcd(struct usb_hcd *hcd,
>>>>  	int retval;
>>>>  	struct usb_device *rhdev;
>>>>  
>>>> +	hcd->flags = 0;
>>>
> 
> I am not sure if this usb_add(remove)_hcd pair is safe and clean enough
> for start/stop host role. From my point, we may need to do like
> .probe/.remove host platform driver interface. In that case, we can make

probe and remove are meant to be called from bus layer.
I do not see a way how OTG framework can call probe/remove of HCD driver.
Some HCDs may be platform devices, some PCI, so different entities are calling
the HCD .probe hook.

> sure the clocks and regulators are off, and hcd will be zero-initialized

why can't we make that sure that is taken care of within the hcd_ops?
Why should some driver keep its regulators and clocks enabled when hcd is stopped?
It doesn't need to. If it is doing so now, it needs to be fixed.

> next time. Assume we are at gadget mode, we may not hope the vbus regulator
> is still on which is for host only. So, this part may need to implement
> by each user.
> 

Yes, correctness of this has to be taken care by each driver.

cheers,
-roger