Re: [Xen-devel] [PATCH 05/11] xen/arm: vpl011: Initialize nr_spis in vgic_init in Xen to atleast 1

[Julien Grall <julien.grall@xxxxxxx>]

On 03/16/2017 06:50 AM, Bhupinder Thakur wrote:
> Hi,
Hi Bhupinder,

> On 5 March 2017 at 13:51, Julien Grall <julien.grall@xxxxxxx> wrote:
> > Hi Bhupinder,
> >
> > Commit title: s/atleat/at least/
> >
> > On 02/21/2017 11:26 AM, Bhupinder Thakur wrote:
> > > Ensure that nr_spis intialized in in vgic_init is atleast 1 to allow
> > > allocation of
> >
> > s/intialized/initialized/ and again s/atleast/at least/
> >
> > > pl011 spi virq.
> > >
> > > Signed-off-by: Bhupinder Thakur <bhupinder.thakur@xxxxxxxxxx>
> > > ---
> > >  xen/arch/arm/vgic.c | 5 +++++
> > >  1 file changed, 5 insertions(+)
> > >
> > > diff --git a/xen/arch/arm/vgic.c b/xen/arch/arm/vgic.c
> > > index 364d5f0..614b3ec 100644
> > > --- a/xen/arch/arm/vgic.c
> > > +++ b/xen/arch/arm/vgic.c
> > > @@ -121,6 +121,11 @@ int domain_vgic_init(struct domain *d, unsigned int
> > > nr_spis)
> > >      /* Limit the number of virtual SPIs supported to (1020 - 32) = 988
> > > */
> > >      if ( nr_spis > (1020 - NR_LOCAL_IRQS) )
> > >          return -EINVAL;
> > > +#ifdef CONFIG_VPL011_CONSOLE
> > > +    /* Atleast 1 spi should be available for assigning to vpl011 */
> > > +    else if ( nr_spis < (1020 - NR_LOCAL_IRQS) )
> > > +        nr_spis += 1;
> > > +#endif
> >
> > Please don't do that. The toolstack should allocated the correct number of
> > SPIs depending on the configuration of the guest.
> Currently there is one parameter "irqs", which can be specified in the
> guest configuration file to specify the list of physical irqs allowed
> to a guest. The nr_spis is set to the maximum value of the irq
> specified in the irqs list. Can I use this parameter to specify the
> irq for pl011? I think not because this parameter is related to
> physical irqs to be allowed to a guest.
nr_spis in the DOMCTL create domain indicates the number of SPIs that 
will be available in the GIC emulation and exposed to the guest via 
GICD_TYPER. The virtual SPIs will be routed in a second step (see 
DOMCTL_bind_pt_irq.
> The other option is to reserve a SPI for pl011 at compile time and use
> that value. Let me know.
Whilst I am ok to have the pl011 SPI number hardcoded, I don't like the 
approach taken in this patch because the toolstack is in charge of the 
guest layout (interrupt, memory...) and not the hypervisor.
The values are hardcoded today because we decided to do a fix layout for 
simplicity. It is likely to be changed in the future.
The toolstack knows how much memory the user requested, the list of 
devices available... So it is the goal of the toolstack to bump the 
number of SPIs before creating the domain if a PL011 will be exposed.
Also, the interaction between the pl011 and the parameter "irqs" in the 
domain configuration file will need to be documented. By that I mean 
explaining from which number the SPIs will be allocated when choosing a 
pl011 enabling.
Note the probably want to allow the user to choose the pl011 IRQ and 
MMIO region. If he doesn't provide any, we would use the default value.
Cheers,

--
Julien Grall

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