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

[Julien Grall <julien.grall@xxxxxxx>]

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).

Cheers,

--
Julien Grall
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