Re: [PATCH v2] MIPS: Add basic R5900 support

["Maciej W. Rozycki" <macro@mips.com>]

Fredrik, John --

 John: can you please see the question below on the machine type you 
previously fiddled with?

> >  Given that the R5900 does not expand DSP support anyhow that sounds 
> > suspicious to me.
> 
> I've taken a closer look at the R5900 changes to the DSP kernel code now:
> 
> The R5900 has four three-operand instructions: MADD, MADDU, MULT and MULTU.
> In addition, it has ten instructions for pipeline 1: MULT1, MULTU1, DIV1,
> DIVU1, MADD1, MADDU1, MFHI1, MFLO1, MTHI1 and MTLO1. Those are the reason
> (parts of) the cpu_has_dsp infrastructure is used, as shown in the patch
> below. What are your thoughts on this?
> 
> The instructions are specific to the R5900, and notably incompatible with
> similar ones in the base MIPS32 architecture. They are also distinct from
> the (also R5900 specific) 128-bit multimedia instructions.

 They're still upper halves of the architectural HI/LO accumulator and 
also used by the 128-bit multiply and divide instructions.  I think they 
should be handled analogously to the 128-bit GPRs, rather than pretending 
they're a crippled version of the DSP ASE.

> By the way, "machine" is set to "Unknown" and "ASEs implemented" is empty
> in /proc/cpuinfo. What would be the proper values for the R5900?

 I have no idea what the machine type is supposed to be set to and why it 
is not omitted by default, given this piece:

		if (mips_get_machine_name())
			seq_printf(m, "machine\t\t\t: %s\n",
				mips_get_machine_name());

I think commit 9169a5d01114 ("MIPS: move mips_{set,get}_machine_name() to 
a more generic place") broke things.  Cc-ing the author for possible 
input.

 ASEs OTOH are specific to MIPS32 and MIPS64 architectures, as per 
respective architecture specification volumes (the MIPS16 ASE might be a 
prominent exception, having been defined as the first ASE ever mid way 
through between the MIPS IV and MIPS32/MIPS64 ISAs).  As the R5900 is not 
a MIPS32 or MIPS64 processor (and has no MIPS16 support) it does not have 
any ASEs implemented.  Vendor-specific architecture extensions do not 
count as ASEs.

  Maciej