Re: [PATCH v19 09/11] arm64: Handle BRBE booting requirements

[Leo Yan]

On Wed, Feb 12, 2025 at 03:21:46PM -0600, Rob Herring wrote:

[...]

> > > +  - If the kernel is entered at EL1 and EL2 is present:
> > > +
> > > +    - BRBCR_EL2.CC (bit 3) must be initialised to 0b1.
> > > +    - BRBCR_EL2.MPRED (bit 4) must be initialised to 0b1.
> >
> > Should clarify BRBCR_EL2.TS to be initialised to 0b00 ?  Arm ARM
> > claims the reset behaviour of the TS field is unknown value.  The
> > assembly code below actually has initializes the TS field as zero.
> 
> Humm, we don't currently care what it is initialized to because the
> timestamp is never used. We would care in the future if we use
> timestamps. Will 0b00 be the only correct value? I'm not sure.

In initializaton phase, if set BRBCR_EL2.TS = 0b00, then the timestamp
will be decided by BRBCR_EL1.TS.  I expect the BRBE driver will always
write BRBCR_EL1.TS.

Thanks,
Leo