Subject: Re: [PATCH v6 01/12] usb: hcd: Initialize hcd->flags to 0
To: Peter Chen <hzpeterchen@gmail.com>
References: <1459865117-7032-1-git-send-email-rogerq@ti.com>
 <1459865117-7032-2-git-send-email-rogerq@ti.com> <87zit72rqz.fsf@intel.com>
 <5704AD76.9080806@ti.com> <20160407094246.GA9963@shlinux2.ap.freescale.net>
CC: Felipe Balbi <balbi@kernel.org>, <stern@rowland.harvard.edu>,
        <gregkh@linuxfoundation.org>, <peter.chen@freescale.com>,
        <dan.j.williams@intel.com>, <jun.li@freescale.com>,
        <mathias.nyman@linux.intel.com>, <tony@atomide.com>,
        <Joao.Pinto@synopsys.com>, <abrestic@chromium.org>,
        <linux-usb@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        <linux-omap@vger.kernel.org>
From: Roger Quadros <rogerq@ti.com>
Message-ID: <57063915.7000700@ti.com>
Date: Thu, 7 Apr 2016 13:40:21 +0300
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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@ti.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