[PATCH v2] usb: gadget: f_hid: Fix zero length packet transfer

[PATCH v2] usb: gadget: f_hid: Fix zero length packet transfer

[William Wu]

Set the hid req->zero flag of ep0/in_ep to true by default,
then the UDC drivers can transfer a zero length packet at
the end if the hid transfer with size divisible to EPs max
packet size according to the USB 2.0 spec.

Signed-off-by: William Wu <william.wu@rock-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..307ea56 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     = 1;
 	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 = 1;
 	req->length = length;
 	status = usb_ep_queue(cdev->gadget->ep0, req, GFP_ATOMIC);
 	if (status < 0)
-- 
2.0.0

Re: [PATCH v2] usb: gadget: f_hid: Fix zero length packet transfer

[Greg KH]

On Mon, Aug 25, 2025 at 12:14:26PM +0800, William Wu wrote:
> Set the hid req->zero flag of ep0/in_ep to true by default,
> then the UDC drivers can transfer a zero length packet at
> the end if the hid transfer with size divisible to EPs max
> packet size according to the USB 2.0 spec.
> 
> Signed-off-by: William Wu <william.wu@rock-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..307ea56 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     = 1;
>  	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 = 1;
>  	req->length = length;
>  	status = usb_ep_queue(cdev->gadget->ep0, req, GFP_ATOMIC);
>  	if (status < 0)
> -- 
> 2.0.0
> 

Hi,

This is the friendly patch-bot of Greg Kroah-Hartman.  You have sent him
a patch that has triggered this response.  He used to manually respond
to these common problems, but in order to save his sanity (he kept
writing the same thing over and over, yet to different people), I was
created.  Hopefully you will not take offence and will fix the problem
in your patch and resubmit it so that it can be accepted into the Linux
kernel tree.

You are receiving this message because of the following common error(s)
as indicated below:

- This looks like a new version of a previously submitted patch, but you
  did not list below the --- line any changes from the previous version.
  Please read the section entitled "The canonical patch format" in the
  kernel file, Documentation/process/submitting-patches.rst for what
  needs to be done here to properly describe this.

If you wish to discuss this problem further, or you have questions about
how to resolve this issue, please feel free to respond to this email and
Greg will reply once he has dug out from the pending patches received
from other developers.

thanks,

greg k-h's patch email bot

[PATCH v2] usb: gadget: f_hid: Fix zero length packet transfer

[William Wu]

Set the hid req->zero flag of ep0/in_ep to true by default,
then the UDC drivers can transfer a zero length packet at
the end if the hid transfer with size divisible to EPs max
packet size according to the USB 2.0 spec.

Signed-off-by: William Wu <william.wu@rock-chips.com>
---
Changelog:

v2:
- set req->zero to 1 instead of check whether the length is divisible by the maxpacket

---
 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..307ea56 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     = 1;
 	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 = 1;
 	req->length = length;
 	status = usb_ep_queue(cdev->gadget->ep0, req, GFP_ATOMIC);
 	if (status < 0)
-- 
2.0.0