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    usb: add helper to extract bits 12:11 of wMaxPacketSize · 541b6fe6
    Felipe Balbi 提交于
    According to USB Specification 2.0 table 9-4,
    wMaxPacketSize is a bitfield. Endpoint's maxpacket
    is laid out in bits 10:0. For high-speed,
    high-bandwidth isochronous endpoints, bits 12:11
    contain a multiplier to tell us how many
    transactions we want to try per uframe.
    
    This means that if we want an isochronous endpoint
    to issue 3 transfers of 1024 bytes per uframe,
    wMaxPacketSize should contain the value:
    
    	1024 | (2 << 11)
    
    or 5120 (0x1400). In order to make Host and
    Peripheral controller drivers' life easier, we're
    adding a helper which returns bits 12:11. Note that
    no care is made WRT to checking endpoint type and
    gadget's speed. That's left for drivers to handle.
    Signed-off-by: NFelipe Balbi <felipe.balbi@linux.intel.com>
    541b6fe6
ch9.h 37.4 KB