Re: [Xen-devel] [PATCH v7 18/28] xen/arm: ITS: Export ITS info to Virtual ITS

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Thu, 2015-09-24 at 12:31 +0100, Julien Grall wrote:
> Hi Ian,
> 
> On 24/09/15 09:27, Ian Campbell wrote:
> > On Thu, 2015-09-24 at 10:56 +0530, Vijay Kilari wrote:
> > 
> > > > > +
> > > > >          plpi = its_get_plpi(pdev, i);
> > > > >          /* TODO: Route lpi */
> > > > >      }
> > > > > @@ -1366,6 +1374,8 @@ static int its_probe(struct dt_device_node
> > > > > *node)
> > > > >      its->phys_size = its_size;
> > > > >      typer = readl_relaxed(its_base + GITS_TYPER);
> > > > >      its->ite_size = ((typer >> 4) & 0xf) + 1;
> > > > > +    its_data.eventID_bits = GITS_TYPER_IDBITS(typer);
> > > > > +    its_data.devID_bits = GITS_TYPER_DEVBITS(typer);
> > > > 
> > > > The 2 fields will be override every time a new ITS node will be
> > > > initialized.
> > > > 
> > > > What ensure that all the ITS have the same number of Event ID and
> > > > Device ID?
> > > 
> > > Nothing of I thing of ensures this at HW level.
> > 
> > The question here is about the behaviour of the software emulation.
> > 
> > >  Either we should
> > > assume that all the ITS
> > > have number of Event and Device ID or we choose lower of all the
> > > ITS?.
> > 
> > Don't we need, if anything, the highest?
> 
> It's worth mentioning that there is no generic mechanism to notify if a
> command is invalid. So passing an out of range DevID and EventID in a
> command may potentially result to crashing Xen because we receive an
> SError.
> 
> So we can use the highest value only if we have all the safety in Xen to
> prevent to send any command invalid out of range value.

Oh, I thought this was the vits (so we could make whatever we wanted work).

If this is the physical ITS thing and these values can differ between
different ITSs in a system then surely these limits need to be recorded in
a per pits location.

Ian.

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