Re: [PATCH] usb: misc: cypress_cy7c63: check control transfer status

[Greg KH <gregkh@linuxfoundation.org>]

On Fri, Jun 19, 2026 at 02:00:53AM +0530, Keshav Verma wrote:
> read_port() currently ignores errors from vendor_command() and always
> returns the cached port value. This can report stale data when the USB
> control transfer fails or returns a short response.
> 
> Return the underlying error for failed transfers and report -EIO if the
> device returns fewer bytes than required.
> 
> Fixes: 9189bfc2df0f ("[PATCH] USB: rename Cypress CY7C63xxx driver to proper name and fix up some tiny things")
> Signed-off-by: Keshav Verma <iganschel@gmail.com>
> ---
>  drivers/usb/misc/cypress_cy7c63.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/usb/misc/cypress_cy7c63.c b/drivers/usb/misc/cypress_cy7c63.c
> index 4a7f955ba85b..8601ee0a1ea3 100644
> --- a/drivers/usb/misc/cypress_cy7c63.c
> +++ b/drivers/usb/misc/cypress_cy7c63.c
> @@ -177,6 +177,10 @@ static ssize_t read_port(struct device *dev, struct device_attribute *attr,
>  	result = vendor_command(cyp, CYPRESS_READ_PORT, read_id, 0);
>  
>  	dev_dbg(&cyp->udev->dev, "Result of vendor_command: %d\n\n", result);
> +	if (result < 0)
> +		return result;
> +	if (result < 2)
> +		return -EIO;
>  
>  	return sprintf(buf, "%d", cyp->port[port_num]);
>  }

You only changed one call to vendor_command() here, why?  Why not fix
this all up by changing vendor_command() to use a better function that
will give you a sane error value, and then check that?

Start with this patch:


diff --git a/drivers/usb/misc/cytherm.c b/drivers/usb/misc/cytherm.c
index d26f460ecdbc..86c4678e23b3 100644
--- a/drivers/usb/misc/cytherm.c
+++ b/drivers/usb/misc/cytherm.c
@@ -51,12 +51,10 @@ static int vendor_command(struct usb_device *dev, unsigned char request,
 			  unsigned char value, unsigned char index,
 			  void *buf, int size)
 {
-	return usb_control_msg(dev, usb_rcvctrlpipe(dev, 0),
-			       request, 
-			       USB_DIR_IN | USB_TYPE_VENDOR | USB_RECIP_OTHER,
-			       value, 
-			       index, buf, size,
-			       USB_CTRL_GET_TIMEOUT);
+	return usb_control_msg_recv(dev, 0, request,
+				    USB_DIR_IN | USB_TYPE_VENDOR | USB_RECIP_OTHER,
+				    value, index, buf, size,
+				    USB_CTRL_GET_TIMEOUT, GFP_KERNEL);
 }
 

And go from there!

thanks,

greg k-h