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Date: Thu, 13 Feb 2025 12:27:19 +0000
From: Leo Yan <leo.yan@arm.com>
To: Rob Herring <robh@kernel.org>
Cc: Will Deacon <will@kernel.org>, Mark Rutland <mark.rutland@arm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Jonathan Corbet <corbet@lwn.net>, Marc Zyngier <maz@kernel.org>,
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Subject: Re: [PATCH v19 09/11] arm64: Handle BRBE booting requirements
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References: <20250202-arm-brbe-v19-v19-0-1c1300802385@kernel.org>
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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