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

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Date:	Wed, 20 Apr 2016 11:15:30 +0300
From:	Roger Quadros <rogerq@...com>
To:	Peter Chen <hzpeterchen@...il.com>,
	Alan Stern <stern@...land.harvard.edu>
CC:	Felipe Balbi <balbi@...nel.org>, <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 19/04/16 04:56, Peter Chen wrote:
> On Mon, Apr 18, 2016 at 10:11:29AM -0400, Alan Stern wrote:
>> On Mon, 18 Apr 2016, 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;
>>>>>
>>>>> seems like this would make more sense in usb_del_hcd() instead.
>>>>>
>>>>
>>>> OK, I'll move it there.
>>>>
>>>
>>> It depends on Alan's comments, whether only usb_add_hcd/usb_del_hcd
>>> pair can be called repeat. If Alan acks it, I have no idea for it.
>>
>> Most of the host controller drivers were not written with this in mind,
>> but I think it would be a good thing to allow.  It would speed up the
>> host/device role switches.
>>
>> This might mean we need to fix up several drivers to make them work 
>> correctly in an OTG environment.  It should be possible to do this.  Is 
>> there any particular reason why it would be difficult for Chipidea?
>>
> 
> I just want to do clean remove at OTG environment, like rmmod, so I did
> this when I worked on chipidea OTG design.
> I am worried if there are some resources dedicated for host device, eg,
> clocks, gpio. etc.
> 
> If OTG framework can know well hcd's add and remove, it is ok for chipidea
> just calling usb_add_hcd/usb_del_hcd currently, but I suggested roger
> adding platform hcd_ops as optional parameter in case the platform
> has special requirement for hcd_ops.
> 
We have 2 users now, omap + dwc3 and sh + EHCI/OHCI and we didn't seem to
observe any issues with the usb_add/del_hcd approach.

Let's keep things minimal for now. In the future, if users need something more
we can always extend the framework.

cheers,
-roger