Re: [Xen-devel] [PATCH 07/19] xen: arm: Annotate trap handler for HCR_EL2.{TWI, TWE, TSC}

[Julien Grall <julien.grall@xxxxxxxxxx>]

Hi Ian,

On 16/04/2015 17:34, Ian Campbell wrote:
> On Fri, 2015-04-03 at 15:05 +0200, Julien Grall wrote:
> > Hi Ian,
> >
> > On 31/03/2015 12:07, Ian Campbell wrote:
> > > Reference the bit which enables the trap and the section/page which
> > > describes what that bit enables.
> > >
> > > These ones are pretty trivial, included for completeness.
> > >
> > > Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
> > > ---
> > >    xen/arch/arm/traps.c |   17 +++++++++++++++++
> > >    1 file changed, 17 insertions(+)
> > >
> > > diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
> > > index c9c98d3..70e1b4d 100644
> > > --- a/xen/arch/arm/traps.c
> > > +++ b/xen/arch/arm/traps.c
> > > @@ -2083,6 +2083,12 @@ asmlinkage void do_trap_hypervisor(struct cpu_user_regs 
> > > *regs)
> > >
> > >        switch (hsr.ec) {
> > >        case HSR_EC_WFI_WFE:
> > > +        /*
> > > +         * HSR_EL2.TWI, HSR_EL2.TWE
> > Typo: I should be HCR not HSR.
> Gah, at least I was consistent pretty much throughout!
>
> > > +         *
> > > +         * ARMv7 (DDI 0406C.b): B1.14.9
> > > +         * ARMv8 (DDI 0487A.d): D1-1505 Table D1-51
> > It's a bit confusing that you are using section for ARMv7 and page for
> > ARMv8.
> I wanted to use section numbers everywhere, since in the ARMv7 ARM they
> are nice and precise. But the ARMv8 ARM doesn't really use them in the
> same way.
>
> In this case D1-1505 is in section D1.15.3 which starts on page D1-1495
> and covers the whole of HCR_EL2, which isn't a useful reference since it
> would be the same for 2/3 of the patches (AKA bits in HCR_EL2) in this
> series. D1-1505 isn't perfect since there is other stuff on that page,
> but it's as close I can get.
Right, it's better to have a specific reference. I was surprised to see 
that ARMv8 didn't have number for small section.
> Bit in the ARMv7 ARM B1.14.9 is exactly about these two traps.
>
> Part of my goal here is to make it so that people (especially me) don't
> spend half their life searching for the doc associated with a given
> HCR_EL2 trap bit.
Thank you for the explanation. When I reviewed the series, it was very 
handy to have a reference to the docs.
Regards,

--
Julien Grall

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