linux-kernel - Re: [PATCH] usb: gadget: f_hid: Fix zero length packet transfer

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Message-ID: <2025082235-fondness-destruct-f8f6@gregkh>
Date: Fri, 22 Aug 2025 06:45:04 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: William Wu <william.wu@...k-chips.com>
Cc: Chris.Wulff@...mp.com, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org, frank.wang@...k-chips.com,
	jianwei.zheng@...k-chips.com, yue.long@...k-chips.com
Subject: Re: [PATCH] usb: gadget: f_hid: Fix zero length packet transfer

On Fri, Aug 22, 2025 at 10:01:58AM +0800, William Wu wrote:
> If the hid transfer with size divisible to EPs max packet
> size, it needs to set the req->zero to true, then the usb
> controller can transfer a zero length packet at the end
> according to the USB 2.0 spec.
> 
> Signed-off-by: William Wu <william.wu@...k-chips.com>
> ---
>  drivers/usb/gadget/function/f_hid.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/usb/gadget/function/f_hid.c b/drivers/usb/gadget/function/f_hid.c
> index 8e1d1e8..8021af3 100644
> --- a/drivers/usb/gadget/function/f_hid.c
> +++ b/drivers/usb/gadget/function/f_hid.c
> @@ -511,7 +511,7 @@ static ssize_t f_hidg_write(struct file *file, const char __user *buffer,
>  	}
>  
>  	req->status   = 0;
> -	req->zero     = 0;
> +	req->zero     = ((count % hidg->in_ep->maxpacket) == 0);
>  	req->length   = count;
>  	req->complete = f_hidg_req_complete;
>  	req->context  = hidg;
> @@ -967,7 +967,7 @@ static int hidg_setup(struct usb_function *f,
>  	return -EOPNOTSUPP;
>  
>  respond:
> -	req->zero = 0;
> +	req->zero = ((length % cdev->gadget->ep0->maxpacket) == 0);
>  	req->length = length;
>  	status = usb_ep_queue(cdev->gadget->ep0, req, GFP_ATOMIC);
>  	if (status < 0)

What commit id does this fix?

thanks,

greg k-h