Re: [Xen-devel] [PATCH 05/28] ARM: GICv3 ITS: map ITS command buffer

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Tue, 14 Feb 2017, Julien Grall wrote:
> Hi Stefano,
> 
> On 02/14/2017 12:59 AM, Stefano Stabellini wrote:
> > On Mon, 30 Jan 2017, Andre Przywara wrote:
> > >  static int its_map_baser(void __iomem *basereg, uint64_t regc, int
> > > nr_items)
> > > @@ -150,6 +191,11 @@ int gicv3_its_init(struct host_its *hw_its)
> > >          }
> > >      }
> > > 
> > > +    hw_its->cmd_buf = its_map_cbaser(hw_its);
> > > +    if ( !hw_its->cmd_buf )
> > > +        return -ENOMEM;
> > > +    writeq_relaxed(0, hw_its->its_base + GITS_CWRITER);
> > 
> > Why this new write?
> 
> This was requested by me. From the spec (8.19.5 in ARM IHI 0069C), the
> reset value of GITS_CWRITER is unknown. So we have to reset the register
> to 0 otherwise the ITS may try to read invalid command as soon as it has
> been enabled.
> 
> FWIW, GITS_CREADR was reset to 0 by the ITS when GITS_CBASER has
> successfully been written (see 8.19.2).

All right, thanks

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