Re: [PATCH v2 10/17] arm64: Enable workaround for TRBE overwrite in FILL mode

[Anshuman Khandual <anshuman.khandual@arm.com>]

On 9/22/21 1:41 PM, Suzuki K Poulose wrote:
> On 22/09/2021 08:23, Anshuman Khandual wrote:
>>
>>
>> On 9/21/21 7:11 PM, Suzuki K Poulose wrote:
>>> Now that we have the work around implmented in the TRBE
>>> driver, add the Kconfig entries and document the errata.
>>>
>>> Cc: Mark Rutland <mark.rutland@arm.com>
>>> Cc: Will Deacon <will@kernel.org>
>>> Cc: Catalin Marinas <catalin.marinas@arm.com>
>>> Cc: Anshuman Khandual <anshuman.khandual@arm.com>
>>> Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
>>> Cc: Mike Leach <mike.leach@linaro.org>
>>> Cc: Leo Yan <leo.yan@linaro.org>
>>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
>>> ---
>>>   Documentation/arm64/silicon-errata.rst |  4 +++
>>>   arch/arm64/Kconfig                     | 39 ++++++++++++++++++++++++++
>>>   2 files changed, 43 insertions(+)
>>>
>>> diff --git a/Documentation/arm64/silicon-errata.rst b/Documentation/arm64/silicon-errata.rst
>>> index d410a47ffa57..2f99229d993c 100644
>>> --- a/Documentation/arm64/silicon-errata.rst
>>> +++ b/Documentation/arm64/silicon-errata.rst
>>> @@ -92,12 +92,16 @@ stable kernels.
>>>   +----------------+-----------------+-----------------+-----------------------------+
>>>   | ARM            | Cortex-A77      | #1508412        | ARM64_ERRATUM_1508412       |
>>>   +----------------+-----------------+-----------------+-----------------------------+
>>> +| ARM            | Cortex-A710     | #2119858        | ARM64_ERRATUM_2119858       |
>>> ++----------------+-----------------+-----------------+-----------------------------+
>>>   | ARM            | Neoverse-N1     | #1188873,1418040| ARM64_ERRATUM_1418040       |
>>>   +----------------+-----------------+-----------------+-----------------------------+
>>>   | ARM            | Neoverse-N1     | #1349291        | N/A                         |
>>>   +----------------+-----------------+-----------------+-----------------------------+
>>>   | ARM            | Neoverse-N1     | #1542419        | ARM64_ERRATUM_1542419       |
>>>   +----------------+-----------------+-----------------+-----------------------------+
>>> +| ARM            | Neoverse-N2     | #2139208        | ARM64_ERRATUM_2139208       |
>>> ++----------------+-----------------+-----------------+-----------------------------+
>>>   | ARM            | MMU-500         | #841119,826419  | N/A                         |
>>>   +----------------+-----------------+-----------------+-----------------------------+
>>>   +----------------+-----------------+-----------------+-----------------------------+
>>> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
>>> index 077f2ec4eeb2..eac4030322df 100644
>>> --- a/arch/arm64/Kconfig
>>> +++ b/arch/arm64/Kconfig
>>> @@ -666,6 +666,45 @@ config ARM64_ERRATUM_1508412
>>>           If unsure, say Y.
>>>   +config ARM64_WORKAROUND_TRBE_OVERWRITE_FILL_MODE
>>> +    bool
>>> +
>>> +config ARM64_ERRATUM_2119858
>>> +    bool "Cortex-A710: 2119858: workaround TRBE overwriting trace data in FILL mode"
>>> +    default y
>>> +    depends on CORESIGHT_TRBE
>>> +    select ARM64_WORKAROUND_TRBE_OVERWRITE_FILL_MODE
>>> +    help
>>> +      This option adds the workaround for ARM Cortex-A710 erratum 2119858.
>>> +
>>> +      Affected Cortex-A710 cores could overwrite upto 3 cache lines of trace
>>> +      data at the base of the buffer (ponited by TRBASER_EL1) in FILL mode in
>>> +      the event of a WRAP event.
>>> +
>>> +      Work around the issue by always making sure we move the TRBPTR_EL1 by
>>> +      256bytes before enabling the buffer and filling the first 256bytes of
>>> +      the buffer with ETM ignore packets upon disabling.
>>> +
>>> +      If unsure, say Y.
>>> +
>>> +config ARM64_ERRATUM_2139208
>>> +    bool "Neoverse-N2: 2139208: workaround TRBE overwriting trace data in FILL mode"
>>> +    default y
>>> +    depends on CORESIGHT_TRBE
>>> +    select ARM64_WORKAROUND_TRBE_OVERWRITE_FILL_MODE
>>> +    help
>>> +      This option adds the workaround for ARM Neoverse-N2 erratum 2139208.
>>> +
>>> +      Affected Neoverse-N2 cores could overwrite upto 3 cache lines of trace
>>> +      data at the base of the buffer (ponited by TRBASER_EL1) in FILL mode in
>>
>> s/ponited/pointed
>>
>>> +      the event of a WRAP event.
>>> +
>>> +      Work around the issue by always making sure we move the TRBPTR_EL1 by
>>> +      256bytes before enabling the buffer and filling the first 256bytes of
>>> +      the buffer with ETM ignore packets upon disabling.
>>> +
>>> +      If unsure, say Y.
>>> +
>>>   config CAVIUM_ERRATUM_22375
>>>       bool "Cavium erratum 22375, 24313"
>>>       default y
>>>
>>
>> The real errata problem description for both these erratums are exactly
>> the same. Rather a more generalized description should be included for
>> the ARM64_WORKAROUND_TRBE_OVERWRITE_FILL_MODE, which abstracts out the
>> problem and a corresponding solution that is implemented in the driver.
>> This should also help us reduce current redundancy.
>>
> 
> The issue is what a user wants to see. A user who wants to configure the
> kernel specifically for a given CPU (think embedded systems), they would
> want to hand pick the errata for the particular CPU. So, moving the help
> text to an implicitly selected Kconfig symbol. I would rather keep this
> as it is to keep it user friendly. This doesn't affect the code size
> anyways.

Understood.

> 
> The other option is to remove all the CPU specific Kconfig symbols and
> update the "title" to reflect both the CPU/erratum numbers.

Hmm, but I guess the current proposal is better instead.