[PATCH] sparc: Add workaround for GRLIB-TN-0011

[Sebastian Huber]

On 23/11/2021 18:13, Joel Sherrill wrote:
> On Tue, Nov 23, 2021 at 9:34 AM Sebastian Huber
> <sebastian.huber at embedded-brains.de> wrote:
>>
>> Affected components are the GR712RC, UT699, UT699E, UT700, and
>> LEON3FT-RTAX.  Strictly, the workaround is only necessary if the MMU is
>> enabled.  Use __FIX_LEON3FT_B2BST to enable the workaround.  This is not
>> 100% appropriate, but the best thing we can use to enable the
>> workaround.
>>
>> Close #4551.
>> ---
>>   cpukit/score/cpu/sparc/cpu_asm.S | 10 ++++++++++
>>   1 file changed, 10 insertions(+)
>>
>> diff --git a/cpukit/score/cpu/sparc/cpu_asm.S b/cpukit/score/cpu/sparc/cpu_asm.S
>> index 45d1495af7..04b2b0119f 100644
>> --- a/cpukit/score/cpu/sparc/cpu_asm.S
>> +++ b/cpukit/score/cpu/sparc/cpu_asm.S
>> @@ -190,6 +190,16 @@ done_flushing:
>>           ! Try to update the is executing indicator of the heir context
>>           mov     1, %g1
>>
>> +#if defined(__FIX_LEON3FT_B2BST)
>> +        /*
>> +         * This is a workaround for GRLIB-TN-0011.  Affected components are the
>> +         * GR712RC, UT699, UT699E, UT700, and LEON3FT-RTAX.  Strictly, the
>> +         * workaround is only necessary if the MMU is enabled.  Using the
>> +         * __FIX_LEON3FT_B2BST is not 100% appropriate, but the best thing we
>> +         * can use to enable the workaround.
>> +         */
>> +.align 16
>> +#endif
> 
> Is there an assumption on the fill pattern here? If the "move 1, %g1" is
> executed, it looks like the code will fall into the alignment fill
> area. If those
> are not guaranteed to be nops, then what instruction(s) are executed?
> 
> It probably is a nop but that should be checked and in the comment.

It is filled with nops.

> 
> And this is in an SMP conditional section but I am unsure if all of those
> are multi-core models.  What does this errata actually cover? Is it that
> swap needs to be aligned? And it is just a coincidence that this is only
> in an SMP build of RTEMS?
> 
> I'm ok with it but the comments and implicit assumptions need to be
> enhanced.

This is just the recommended workaround for the errata. The errata is 
mentioned in the comment. I don't think we should duplicate the errata 
description in the code.

> 
>>   .Ltry_update_is_executing:
>>
>>           swap    [%o1 + SPARC_CONTEXT_CONTROL_IS_EXECUTING_OFFSET], %g1
>> --
>> 2.31.1
>>
>> _______________________________________________
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