Changeset 79784ef8 in mainline

Timestamp:

2011-05-08T12:46:20Z (13 years ago)

Author:

Vojtech Horky <vojtechhorky@…>

Branches:

lfn, master, serial, ticket/834-toolchain-update, topic/msim-upgrade, topic/simplify-dev-export

Children:

84de606d

Parents:

faf498d

Message:

Add comment how device "learns" its USB address

File:

• uspace/lib/drv/include/usb_iface.h (modified) (1 diff)

uspace/lib/drv/include/usb_iface.h

@@ -49 +49 @@
          * - arbitrary error code if returned by remote implementation
          * - EOK - handle found, first parameter contains the USB address
+         *
+         * The handle must be the one used for binding USB address with
+         * it (IPC_M_USBHC_BIND_ADDRESS), otherwise the host controller
+         * (that this request would eventually reach) would not be able
+         * to find it.
+         * The problem is that this handle is actually assigned to the
+         * function inside driver of the parent device (usually hub driver).
+         * To bypass this problem, the initial caller specify handle as
+         * zero and the first parent assigns the actual value.
+         * See usb_iface_get_address_hub_child_impl() implementation
+         * that could be assigned to device ops of a child device of in a
+         * hub driver.
+         * For example, the USB multi interface device driver (MID)
+         * passes this initial zero without any modification because the
+         * handle must be resolved by its parent.
          */
         IPC_M_USB_GET_ADDRESS,