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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: Fri, 31 Jul 2020 23:42:52 +0000
Message-ID: <20200731234224.GA13414@b29397-desktop> (raw)
In-Reply-To: <20200731141248.GC36650@rowland.harvard.edu>

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.

-- 

Thanks,
Peter Chen

  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 [this message]
2020-08-01  6:53             ` Peter Chen
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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