On Tue, 29 Apr 2014, David Laight wrote:
> From: Dan Williams
> > Before we add another 2 bitfields to the port state, convert it to an
> > unsigned long and use bitops helpers to manipulate it. This later
> > enables setting bits to request action without worrying about colliding
> > updates. In particular, a flag to request that the child device be
> > woken up when the port restores power is added in a later patch.
> ...
> > struct usb_port {
> > struct usb_device *child;
> > @@ -96,8 +95,9 @@ struct usb_port {
> > enum usb_port_connect_type connect_type;
> > usb_port_location_t location;
> > u8 portnum;
> > - unsigned power_is_on:1;
> > - unsigned did_runtime_put:1;
> > + #define USB_PORTDEV_POWER 0
> > + #define USB_PORTDEV_DID_RUNTIME_PUT 1
> > + unsigned long flags;
> > };
> ...
>
>
> An alternative is to 'waste' 7 bits and use byte-sized fields
> for the separate flags.
> I doubt the size of the data structure matters.
> (Or do we have to worry about cpus that use RMW cycles for byte writes?)
We do.
Another way to avoid the waste is to move the flags into the usb_hub
structure.
Alan Stern
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