• Alan Stern's avatar
    [PATCH] USB: Consider power budget when choosing configuration · 55c52718
    Alan Stern authored
    This patch (as609) changes the way we keep track of power budgeting for
    USB hubs and devices, and it updates the choose_configuration routine to
    take this information into account.  (This is something we should have
    been doing all along.)  A new field in struct usb_device holds the amount
    of bus current available from the upstream port, and the usb_hub structure
    keeps track of the current available for each downstream port.
    
    Two new rules for configuration selection are added:
    
    	Don't select a self-powered configuration when only bus power
    	is available.
    
    	Don't select a configuration requiring more bus power than is
    	available.
    
    However the first rule is #if-ed out, because I found that the internal
    hub in my HP USB keyboard claims that its only configuration is
    self-powered.  The rule would prevent the configuration from being chosen,
    leaving the hub & keyboard unconfigured.  Since similar descriptor errors
    may turn out to be fairly common, it seemed wise not to include a rule
    that would break automatic configuration unnecessarily for such devices.
    
    The second rule may also trigger unnecessarily, although this should be
    less common.  More likely it will annoy people by sometimes failing to
    accept configurations that should never have been chosen in the first
    place.
    
    The patch also changes usbcore's reaction when no configuration is
    suitable.  Instead of raising an error and rejecting the device, now
    the core will simply leave the device unconfigured.  People can always
    work around such problems by installing configurations manually through
    sysfs.
    Signed-off-by: default avatarAlan Stern <stern@rowland.harvard.edu>
    Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@suse.de>
    55c52718
message.c 45.8 KB