From: Suzuki K Poulose <suzuki.poulose@arm.com>
To: Alexandru Elisei <alexandru.elisei@arm.com>,
Anshuman Khandual <anshuman.khandual@arm.com>,
linux-arm-kernel@lists.infradead.org
Cc: mark.rutland@arm.com, Andre.Przywara@arm.com, james.morse@arm.com
Subject: Re: [boot-wrapper] [PATCH] aarch64: Enable TRBE for the non-secure world
Date: Fri, 12 Feb 2021 15:44:57 +0000 [thread overview]
Message-ID: <81d47675-c628-1bb9-d410-46579f4b5175@arm.com> (raw)
In-Reply-To: <0d87e2a5-1c9a-9a8a-96e2-0b335d7445e7@arm.com>
On 2/12/21 2:31 PM, Alexandru Elisei wrote:
> Hello Anshuman,
>
> On 2/11/21 11:26 AM, Anshuman Khandual wrote:
>> MDCR_EL3.NSTB resets to an UNKNOWN value. Configure it to allow the trace
>> buffer to use non-secure memory and to permit direct register accesses from
>> the non-secure world. Before that, just check AA64DFR0_EL1.TraceBuffer and
>> make sure TRBE is implemented. We still continue to reset MDCR_EL3 register
>> to zero with the exception of MDCR_EL3.NSPB and MDCR_EL3.NSTB.
>>
>> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
>> ---
>> arch/aarch64/boot.S | 8 ++++++++
>> 1 file changed, 8 insertions(+)
>>
>> diff --git a/arch/aarch64/boot.S b/arch/aarch64/boot.S
>> index 37f4b98..e47cf59 100644
>> --- a/arch/aarch64/boot.S
>> +++ b/arch/aarch64/boot.S
>> @@ -71,6 +71,14 @@ _start:
>> ldr x1, =(0x3 << 12)
>> orr x0, x0, x1
>>
>> +1: mrs x1, id_aa64dfr0_el1
>> + ubfx x1, x1, #44, #4
>> + cbz x1, 1f
>> +
>> + // Enable TRBE for the non-secure world.
>> + ldr x1, =(0x3 << 24)
>> + orr x0, x0, x1
>> +
>> 1: msr mdcr_el3, x0 // Disable traps to EL3
>>
>> mrs x0, id_aa64pfr0_el1
>
> That's strange, I'm looking at ARM DDI 0487G.a and bits [44:47] from
> ID_AA64DFR0_EL1 are RES0 and there is no TraceBuffer field; bits [24:25] of
> MDCR_EL3 are also RES0 and I searched the entire file for the NSTB field, could
> not find it. Do I have an outdated version of the architecture?
They are not in the Arm ARM. These are part of the Future Architecture
technology changes, for which the register defintions are available here :
https://developer.arm.com/documentation/ddi0601/2020-12/AArch64-Registers/
Cheers
Suzuki
>
> Thanks,
>
> Alex
>
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next prev parent reply other threads:[~2021-02-12 15:46 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-11 11:26 [boot-wrapper] [PATCH] aarch64: Enable TRBE for the non-secure world Anshuman Khandual
2021-02-12 14:31 ` Alexandru Elisei
2021-02-12 15:44 ` Suzuki K Poulose [this message]
2021-02-12 17:28 ` Alexandru Elisei
2021-02-12 17:33 ` Alexandru Elisei
2021-02-25 18:33 ` Mark Rutland
2021-02-25 18:30 ` Mark Rutland
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