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95 lines
3.6 KiB
Text
95 lines
3.6 KiB
Text
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The U-Boot Driver Model Project
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===============================
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USB analysis
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============
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Marek Vasut <marek.vasut@gmail.com>
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2012-02-16
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I) Overview
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-----------
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1) The USB Host driver
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----------------------
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There are basically four or five USB host drivers. All such drivers currently
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provide at least the following fuctions:
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usb_lowlevel_init() ... Do the initialization of the USB controller hardware
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usb_lowlevel_stop() ... Do the shutdown of the USB controller hardware
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usb_event_poll() ...... Poll interrupt from USB device, often used by KBD
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submit_control_msg() .. Submit message via Control endpoint
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submit_int_msg() ...... Submit message via Interrupt endpoint
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submit_bulk_msg() ..... Submit message via Bulk endpoint
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This allows for the host driver to be easily abstracted.
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2) The USB hierarchy
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--------------------
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In the current implementation, the USB Host driver provides operations to
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communicate via the USB bus. This is realised by providing access to a USB
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root port to which an USB root hub is attached. The USB bus is scanned and for
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each newly found device, a struct usb_device is allocated. See common/usb.c
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and include/usb.h for details.
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II) Approach
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------------
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1) The USB Host driver
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----------------------
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Converting the host driver will follow the classic driver model consideration.
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Though, the host driver will have to call a function that registers a root
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port with the USB core in it's probe() function, let's call this function
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usb_register_root_port(&ops);
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This will allow the USB core to track all available root ports. The ops
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parameter will contain structure describing operations supported by the root
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port:
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struct usb_port_ops {
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void (*usb_event_poll)();
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int (*submit_control_msg)();
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int (*submit_int_msg)();
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int (*submit_bulk_msg)();
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}
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2) The USB hierarchy and hub drivers
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------------------------------------
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Converting the USB heirarchy should be fairy simple, considering the already
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dynamic nature of the implementation. The current usb_hub_device structure
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will have to be converted to a struct instance. Every such instance will
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contain components of struct usb_device and struct usb_hub_device in it's
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private data, providing only accessors in order to properly encapsulate the
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driver.
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By registering the root port, the USB framework will instantiate a USB hub
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driver, which is always present, the root hub. The root hub and any subsequent
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hub instance is represented by struct instance and it's private data contain
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amongst others common bits from struct usb_device.
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Note the USB hub driver is partly defying the usual method of registering a
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set of callbacks to a particular core driver. Instead, a static set of
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functions is defined and the USB hub instance is passed to those. This creates
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certain restrictions as of how the USB hub driver looks, but considering the
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specification for USB hub is given and a different type of USB hub won't ever
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exist, this approach is ok:
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- Report how many ports does this hub have:
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uint get_nr_ports(struct instance *hub);
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- Get pointer to device connected to a port:
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struct instance *(*get_child)(struct instance *hub, int port);
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- Instantiate and configure device on port:
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struct instance *(*enum_dev_on_port)(struct instance *hub, int port);
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3) USB device drivers
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---------------------
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The USB device driver, in turn, will have to register various ops structures
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with certain cores. For example, USB disc driver will have to register it's
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ops with core handling USB discs etc.
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