On Tue, Apr 28, 2009 at 01:54:07AM -0700, David Brownell wrote:
> On Tuesday 28 April 2009, Oliver Neukum wrote:
> > Am Dienstag 28 April 2009 04:52:34 schrieb Sarah Sharp:
> > > +/**
> > > + * struct doorbell_array
> > > + *
> > > + * Section 5.6
> > > + */
> > > +struct xhci_doorbell_array {
> > > + u32 doorbell[256];
> > > +} __attribute__ ((packed));
> >
> > If you declare this packed, does gcc still give you atomic writes on
> > all platforms or will it write bytewise?
No idea. :)
> For that matter ... why "packed"? To ensure that it can
> be un-aligned? I thought it was pretty much guaranteed
> that an array of same-size values will have no padding. :)
Again, I don't know much about this area. This structure resides in the
register space of the host controller, so I didn't want any padding. I
had noticed that EHCI makes sure to add the packed attribute to all its
register structures, so I added it here too. The struct
xhci_doorbell_array pointer in xhci_hcd is declared as __iomem.
It would be helpful for someone to explain when to use packed and what
its implications are.
Sarah Sharp
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