On Thu, Sep 07, 2017 at 03:53:07AM -0600, Jan Beulich wrote: > >>> On 14.08.17 at 16:28, <roger....@citrix.com> wrote: > > + > > + /* > > + * The PCI Local Bus Specification suggests writing ~0 to both the high > > + * and the low part of the BAR registers before attempting to read back > > + * the size. > > + * > > + * However real device BARs registers (at least the ones I've tried) > > + * will return the size of the BAR just by having written ~0 to one > > half > > + * of it, independently of the value of the other half of the register. > > + * Hence here Xen will switch to returning the size as soon as one half > > + * of the BAR register has been written with ~0. > > + */ > > I don't believe this is correct behavior (but I'd have to play with > some hardware to see whether I can confirm the behavior you > describe): How would you place a BAR at, say, 0x1ffffff0?
I don't think it's 'correct' behavior either, but FreeBSD has been sizing BARs like that, and nobody noticed any issues. I just fixed it recently: https://svnweb.freebsd.org/base/head/sys/dev/pci/pci.c?r1=312250&r2=321863 Roger. _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org https://lists.xen.org/xen-devel
