Re: [PATCH 1/3] usb: xhci: Add support for eUSB2v2 1024-byte bulk packet size

[Oliver Neukum]

On 17.07.26 12:44, Pawel Laszczak via B4 Relay wrote:
> From: Pawel Laszczak <pawell@xxxxxxxxxxx>

[..]
> index 75e2bfd744a9..3b4f7aedd381 100644
> --- a/drivers/usb/core/message.c
> +++ b/drivers/usb/core/message.c
> @@ -2007,6 +2007,65 @@ int usb_set_wireless_status(struct usb_interface *iface,
>   }
>   EXPORT_SYMBOL_GPL(usb_set_wireless_status);
>   
> +/*
> + * eusb_update_max_packet - set or restore max packet size
> + * @udev: target device
> + * @cp: if NULL restore MPS to 512 else set 1024
> + *
> + * This request is specific to eUSB2v2.
> + * An eUSB2v2 peripheral will revert the maximum packet size to 512
> + * for bulk endpoints after bus reset, disconnect and deconfiguration.
> + * This function allows updating the max packet size for BULK endpoints
> + * to 1024 after above events.
> + */
> +static void eusb_update_max_packet(struct usb_device *udev, struct usb_host_config *cp)

This has interesting implications for error handling. The command
has to be redone before reset_resume() and post_reset().
Hence if this fails in these cases you'll change the packet size
behind a driver's back. The same happens if it initially failed
but succeeds before these two operations, only in the other direction.

IMHO if this operation fails before post_reset() or reset_resume(),
the driver will have to be unbound. Likewise if it had failed before
binding a driver, the failure has to be recorded and the command omitted
before post_reset() or reset_resume().

In any case, this function has to return errors.

	Regards
		Oliver