Re: [PATCH] MdeModulePkg/UsbBusDxe: Return error when the device is not present

["Laszlo Ersek" <lersek@redhat.com>]

On 07/31/19 08:25, Marcin Wojtas wrote:
> Until now, during the USB device enumeration when its PortState
> USB_PORT_STAT_CONNECTION bit was not set, the stack was not informed
> that the device is not present. Fix that by returning appropriate
> error code.
> 
> Change-Id: I588f82b987993e9755f64ce76cde9eb690ef1d54
> Signed-off-by: Marcin Wojtas <mw@semihalf.com>
> ---
>  MdeModulePkg/Bus/Usb/UsbBusDxe/UsbEnumer.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/MdeModulePkg/Bus/Usb/UsbBusDxe/UsbEnumer.c b/MdeModulePkg/Bus/Usb/UsbBusDxe/UsbEnumer.c
> index be9d9bd..ab1db15 100644
> --- a/MdeModulePkg/Bus/Usb/UsbBusDxe/UsbEnumer.c
> +++ b/MdeModulePkg/Bus/Usb/UsbBusDxe/UsbEnumer.c
> @@ -719,6 +719,7 @@ UsbEnumerateNewDev (
>  
>    if (!USB_BIT_IS_SET (PortState.PortStatus, USB_PORT_STAT_CONNECTION)) {
>      DEBUG ((EFI_D_ERROR, "UsbEnumerateNewDev: No device present at port %d\n", Port));
> +    Status = EFI_NOT_FOUND;
>      goto ON_ERROR;
>    } else if (USB_BIT_IS_SET (PortState.PortStatus, USB_PORT_STAT_SUPER_SPEED)){
>      Child->Speed      = EFI_USB_SPEED_SUPER;
> 

I think the patch is correct, based on a quite superficial analysis (i.e. without actual knowledge of USB specifics on my part).

The reason is that Status is EFI_SUCCESS when the "goto" statement is reached, due to the preceding context

  Status = HubApi->GetPortStatus (HubIf, Port, &PortState);

  if (EFI_ERROR (Status)) {
    DEBUG ((EFI_D_ERROR, "UsbEnumerateNewDev: failed to get speed of port %d\n", Port));
    goto ON_ERROR;
  }

And, the ON_ERROR label is documented as:

ON_ERROR:
  //
  // If reach here, it means the enumeration process on a given port is interrupted due to error.
  // [...]
  //
  return Status;

We shouldn't report success when there is no device present on the port.

I think EFI_NOT_FOUND is a suitable error code; while it is not listed explicitly in the leading comment on the function, it does fit under

  @retval Others                Failed to enumerate the device.

Marcin, can you please remove the "Change-Id" tag from the commit message? (Or the MdeModulePkg maintainers could do that, just before they push the patch.)

With "Change-Id" removed:

Reviewed-by: Laszlo Ersek <lersek@redhat.com>

Thanks
Laszlo