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From: Peter Chen <peter.chen@nxp.com>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	"balbi@kernel.org" <balbi@kernel.org>,
	"linux-usb@vger.kernel.org" <linux-usb@vger.kernel.org>,
	dl-linux-imx <linux-imx@nxp.com>
Subject: RE: [PATCH 1/1] usb: gadget: core: wait gadget device .release finishing at usb_del_gadget_udc
Date: Sat, 1 Aug 2020 06:53:40 +0000
Message-ID: <DB8PR04MB7162CC76A1957F83F6079F688B4F0@DB8PR04MB7162.eurprd04.prod.outlook.com> (raw)
In-Reply-To: <20200731234224.GA13414@b29397-desktop>

 
> 
> On 20-07-31 10:12:48, Alan Stern wrote:
> > On Fri, Jul 31, 2020 at 02:06:20PM +0000, Peter Chen wrote:
> > > On 20-07-31 14:25:20, Greg Kroah-Hartman wrote:
> > > > On Fri, Jul 31, 2020 at 12:11:32PM +0000, Peter Chen wrote:
> > > >
> > > > Grab a reference from somewhere else and do not give it up for a
> > > > long time.
> > > >
> > >
> > > So wait_for_completion_timeout is suitable? The similar use case is
> > > when we open the file at the USB Drive at Windows, and we click
> > > "Eject", it will say "The device is currently in use", and refuse our "Eject"
> > > operation.
> > >
> > > When we try to remove the gadget, if the gadget is in use, we could
> > > refuse the remove operation, reasonable?
> >
> > No, the real solution is to fix the UDC drivers.  They need to
> > allocate the gadget structure dynamically instead of reusing it.  And
> > they should have a real release routine that deallocates the gadget structure.
> >
> > Alan Stern
> 
> So, the basic routine should like below. I thought the usb_gadget should be
> deallocated before the UDC driver remove itself (UDC device is the parent of
> usb_gadget device), I may not need to wrong about it, it is just a memory region, it
> could release later.
> 
> xxx_udc_release(struct device *gadget_dev) {
> 	struct usb_gadget *gadget = container_of(gadget_dev, struct
> 			usb_gadget, dev);
> 	kfree(gadget);
> }
> 
> 
> xxx_udc_probe(pdev)
> {
> 	udc_priv_data = kzalloc(sizeof(*udc_priv_data), GFP_KERNEL);
> 	gadget = kzalloc(sizeof(struct usb_gadget), GFP_KERNEL);
> 	udc_priv_data->gadget = gadget;
> 	...
> 	usb_add_gadget_udc_release(&pdev->dev, gadget, xxx_udc_release);
> 
> }
> 
> At xxx_udc_remove(pdev)
> {
> 	usb_del_gadget_udc(udc_priv_data->gadget);
> 	/* need to never reference udc_priv_data->gadget any more */
> 	udc_priv_data other deinit;
> 	kfree(udc_priv_data);
> }
> 
> Since all structures xxx_udc_release uses are common one, it could replace
> usb_udc_nop_release at udc/core.c.
> 
 
Since gadget structure is allocated at UDC drivers, I think it should be freed at
the same place. Current common release function at udc/core.c may not a
good idea per our discussion.

Peter

  reply index

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-31  9:59 Peter Chen
2020-07-31 11:55 ` Greg Kroah-Hartman
2020-07-31 12:11   ` Peter Chen
2020-07-31 12:25     ` Greg Kroah-Hartman
2020-07-31 14:06       ` Peter Chen
2020-07-31 14:12         ` Alan Stern
2020-07-31 23:42           ` Peter Chen
2020-08-01  6:53             ` Peter Chen [this message]
2020-08-01  7:04               ` Jun Li
2020-08-01 15:44               ` Alan Stern
2020-07-31 14:16         ` Greg Kroah-Hartman

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