Re: [Qemu-devel] [PATCH v7 04/20] target/mips: Add and integrate MXU decoding engine placeholder

[Aleksandar Markovic]

> Subject: Re: [PATCH v7 04/20] target/mips: Add and integrate MXU decoding 
> engine > placeholder
> 
> > Is the best way to implement this to include processing of MUL, CLZ,
> > CLO, SDBBP instructions into decode_opc_mxu as their encodings aren't
> > overlaid by MXU instructions considering MIPS SPECIAL2 instruction
> > pool and MXU Instruction Set?
> 
> The problem is that we don't have the documentation for Ingenic's base
> instruction set. My understanding is that Craig established necessity of
> including non-MXU MUL into decode_opc_mxu() by experimentation,
> or by looking at Ingenic's toolchain source code.
> 
> Note that CLZ, CLO, SDBBP are moved from SPECIAL2 to another
> place in opcode space in MIPS R6.
> 
> Craig, can you offer any insight on CLZ, CLO, SDBBP in Ingenic's base
> instruction set? They are in SPECIAL2 opcode space for MIPS pre-R6.
> 
> Worse come to worst, I recommend adding "TODO" comment to an
> appropriate place in decode_opc_mxu(), and go forward without handling
> CLZ, CLO, SDBBP - given that all changes in this series are just the first
> phase of implementing MXU support - they won't affect any production
> code at this moment.
> 

I think this comment should be added to the decode_opc_mxu(), within patch 11:

    /*
     * TODO: Investigate necessity of including handling of
     * CLZ, CLO, SDBB in this function, as they belong to
     * SPECIAL2 opcode space for regular pre-R6 MIPS ISAs.
     */

Thanks,
Aleksandar