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From: Alan Stern <stern@rowland.harvard.edu>
To: Peter Chen <peter.chen@nxp.com>
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 11:44:36 -0400
Message-ID: <20200801154436.GB65766@rowland.harvard.edu> (raw)
In-Reply-To: <DB8PR04MB7162CC76A1957F83F6079F688B4F0@DB8PR04MB7162.eurprd04.prod.outlook.com>

On Sat, Aug 01, 2020 at 06:53:40AM +0000, Peter Chen wrote:
> > 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);
> > }

That would work.  It doesn't have to be done exactly this way.  
Depending on the driver's needs, you could do:

xxx_udc_release(struct device *dev)
{
	udc_priv_data = dev_get_drvdata(dev);
	kfree(udc_priv_data);
}

xxx_udc_probe(pdev)
{
	udc_priv_data = kzalloc(sizeof(*udc_priv_data), GFP_KERNEL);
	dev_set_drvdata(&udc_priv_data->gadget.dev, udc_priv_data);
	platform_set_drvdata(pdev, udc_priv_data);
	...
	usb_add_gadget_udc_release(&pdev->dev, &udc_priv_data->gadget,
			xxx_udc_release);
}

xxx_udc_remove(pdev)
{
	udc_priv_data = platform_get_drvdata(pdev);
	usb_del_gadget_udc(&udc_priv_data->gadget);
}

In other words, embed the struct gadget inside the udc_priv_data 
structure.  The difference is whether you want to keep the udc_priv_data 
structure hanging around even while the controller is in host mode; if 
you do then your approach (a separate struct gadget) is better.  For a 
peripheral-only controller, my approach would be better.

> > Since all structures xxx_udc_release uses are common one, it could replace
> > usb_udc_nop_release at udc/core.c.

Yes, it could.  But first all the UDC drivers would have to be modified.

> 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.

Agreed.

Alan Stern

  parent 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
2020-08-01  7:04               ` Jun Li
2020-08-01 15:44               ` Alan Stern [this message]
2020-07-31 14:16         ` Greg Kroah-Hartman

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