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

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Date:	Fri, 8 Apr 2016 09:01:30 +0800
From:	Peter Chen <hzpeterchen@...il.com>
To:	Roger Quadros <rogerq@...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 Thu, Apr 07, 2016 at 01:40:21PM +0300, Roger Quadros wrote:
> 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.
> 

Well, you may misunderstand me. I mean your hcd_ops->start or ->stop
is hard to be a general one which only calls usb_hcd_add or
usb_hcd_remove. It needs to implement like .probe or .remove at platform
driver, some example code like host_start and host_stop at
drivers/usb/chipidea/host.c.

-- 

Best Regards,
Peter Chen