linux-kernel - Re: [PATCH] usb: udc: Add trace event for usb_gadget_set

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Message-ID: <2025090657-unpinned-unnatural-2ccd@gregkh>
Date: Sat, 6 Sep 2025 15:16:47 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: Kuen-Han Tsai <khtsai@...gle.com>
Cc: royluo@...gle.com, jkeeping@...usicbrands.com,
	stern@...land.harvard.edu, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usb: udc: Add trace event for usb_gadget_set_state

On Mon, Aug 18, 2025 at 04:27:19PM +0800, Kuen-Han Tsai wrote:
> While the userspace program can be notified of gadget state changes,
> timing issue can lead to missed transitions when reading the state
> value.
> 
> Introduce a trace event for usb_gadget_set_state to reliably track state
> transitions.
> 
> Signed-off-by: Kuen-Han Tsai <khtsai@...gle.com>
> ---
>  drivers/usb/gadget/udc/core.c  | 1 +
>  drivers/usb/gadget/udc/trace.h | 5 +++++
>  2 files changed, 6 insertions(+)
> 
> diff --git a/drivers/usb/gadget/udc/core.c b/drivers/usb/gadget/udc/core.c
> index d709e24c1fd4..e28fea614496 100644
> --- a/drivers/usb/gadget/udc/core.c
> +++ b/drivers/usb/gadget/udc/core.c
> @@ -1125,6 +1125,7 @@ void usb_gadget_set_state(struct usb_gadget *gadget,
>  {
>  	gadget->state = state;
>  	schedule_work(&gadget->work);
> +	trace_usb_gadget_set_state(gadget, 0);

Will this show the state the gadget has been set to?  And why not just
do that in the work callback, as that is when it really happens.

What is the output of this trace line?

thanks,

greg k-h