linux-kernel - Re: [PATCH v12 6/6] usb: gadget: f_ecm: Add suspend/resume and remote wakeup support

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Date:   Fri, 17 Mar 2023 21:28:38 +0000
From:   Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To:     Elson Serrao <quic_eserrao@...cinc.com>
CC:     Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "quic_wcheng@...cinc.com" <quic_wcheng@...cinc.com>,
        "quic_jackp@...cinc.com" <quic_jackp@...cinc.com>
Subject: Re: [PATCH v12 6/6] usb: gadget: f_ecm: Add suspend/resume and remote
 wakeup support

On Fri, Mar 17, 2023, Elson Serrao wrote:
> 
> 
> On 3/16/2023 5:11 PM, Thinh Nguyen wrote:
> > On Thu, Mar 16, 2023, Elson Roy Serrao wrote:
> > > When host sends a suspend notification to the device, handle
> > > the suspend callbacks in the function driver. Enhanced super
> > > speed devices can support function suspend feature to put the
> > > function in suspend state. Handle function suspend callback.
> > > 
> > > Depending on the remote wakeup capability the device can either
> > > trigger a remote wakeup or wait for the host initiated resume to
> > > start data transfer again.
> > > 
> > > Signed-off-by: Elson Roy Serrao <quic_eserrao@...cinc.com>
> > > ---
> > >   drivers/usb/gadget/function/f_ecm.c   | 71 +++++++++++++++++++++++++++++++++++
> > >   drivers/usb/gadget/function/u_ether.c | 63 +++++++++++++++++++++++++++++++
> > >   drivers/usb/gadget/function/u_ether.h |  4 ++
> > >   3 files changed, 138 insertions(+)
> > > 
> > > diff --git a/drivers/usb/gadget/function/f_ecm.c b/drivers/usb/gadget/function/f_ecm.c
> > > index a7ab30e..c43cd557 100644
> > > --- a/drivers/usb/gadget/function/f_ecm.c
> > > +++ b/drivers/usb/gadget/function/f_ecm.c
> > > @@ -633,6 +633,8 @@ static void ecm_disable(struct usb_function *f)
> > >   	usb_ep_disable(ecm->notify);
> > >   	ecm->notify->desc = NULL;
> > > +	f->func_suspended = false;
> > > +	f->func_wakeup_armed = false;
> > >   }
> > >   /*-------------------------------------------------------------------------*/
> > > @@ -885,6 +887,71 @@ static struct usb_function_instance *ecm_alloc_inst(void)
> > >   	return &opts->func_inst;
> > >   }
> > > +static void ecm_suspend(struct usb_function *f)
> > > +{
> > > +	struct f_ecm *ecm = func_to_ecm(f);
> > > +	struct usb_composite_dev *cdev = ecm->port.func.config->cdev;
> > > +
> > > +	if (f->func_suspended) {
> > > +		DBG(cdev, "Function already suspended\n");
> > > +		return;
> > > +	}
> > > +
> > > +	DBG(cdev, "ECM Suspend\n");
> > > +
> > > +	gether_suspend(&ecm->port);
> > > +}
> > > +
> > > +static void ecm_resume(struct usb_function *f)
> > > +{
> > > +	struct f_ecm *ecm = func_to_ecm(f);
> > > +	struct usb_composite_dev *cdev = ecm->port.func.config->cdev;
> > > +
> > > +	/*
> > > +	 * If the function is in USB3 Function Suspend state, resume is
> > > +	 * canceled. In this case resume is done by a Function Resume request.
> > > +	 */
> > > +	if (f->func_suspended)
> > > +		return;
> > > +
> > > +	DBG(cdev, "ECM Resume\n");
> > > +
> > > +	gether_resume(&ecm->port);
> > > +}
> > > +
> > > +static int ecm_get_status(struct usb_function *f)
> > > +{
> > > +	struct usb_configuration *c = f->config;
> > > +
> > > +	/* D0 and D1 bit set to 0 if device is not wakeup capable */
> > > +	if (!(USB_CONFIG_ATT_WAKEUP & c->bmAttributes))
> > > +		return 0;
> > > +
> > > +	return (f->func_wakeup_armed ? USB_INTRF_STAT_FUNC_RW : 0) |
> > > +		USB_INTRF_STAT_FUNC_RW_CAP;
> > > +}
> > 
> > Why do we need to implement ecm_get_status if it's already handled in
> > composite.c now?
> > 
> 
> Yes this can be removed now. Will modify accordingly.
> > > +
> > > +static int ecm_func_suspend(struct usb_function *f, u8 options)
> > > +{
> > > +	struct usb_composite_dev *cdev = f->config->cdev;
> > > +
> > > +	DBG(cdev, "func susp %u cmd\n", options);
> > > +
> > > +	if (options & (USB_INTRF_FUNC_SUSPEND_LP >> 8)) {
> > 
> > This feature selector doesn't indicate whether it's SetFeature or
> > ClearFeature request. ecm_func_suspend is supposed to be for
> > SetFeature(suspend) only. Perhaps we may have to define func_resume()
> > for ClearFeature(suspend)?
> > 

> Host uses the same feature selector FUNCTION_SUSPEND for function suspend
> and function resume and func_suspend() callback can be used to
> handle both the cases ? The distinction comes whether it is a

How do you plan to handle that? Pass this info in some unused/reserved
bit of the "options" argument? Introduce a new parameter to the
func_suspend()?

If that's the case, then you need to update the document on
func_suspend() to also support ClearFeature(suspend). Right now it's
documented for SetFeature only. Also, make sure that other existing
function drivers will not break because of the change of the
func_suspend behavior.

> SetFeature(FUNCTION_SUSPEND) or ClearFeature(FUNCTION_SUSPEND) which can be
> easily done in the func_suspend callback itself. We can add another callback
> func_resume specific to ClearFeature(FUNCTION_SUSPEND) but wont that be
> redundant and more callback handling on function driver/composite side as
> well? Please let me know your opinion.
> 

We actually didn't properly define func_suspend and its counter part. It
seems cleaner to me to introduce func_resume as it seems more intuitive
and easier to read. Let me know how you plan to use func_suspend() for
both cases.

Thanks,
Thinh