union/struct representations for MAS Registers

union/struct representations for MAS Registers

[Jimi Xenidis]

I have some and use them in some code, they represent ISA 2.06 MAVN=3D1 =
(version 2)
Can I keep them?
if so, should I put them somewhere useful to others?

Examples:
union mas1 {
	u32 _val;
	struct {
		u32 v:1;
		u32 iprot:1;
		u32 tid:14;
		u32 _reserved_1:2;
		u32 ind:1;
		u32 ts:1;
		u32 tsize:4;
		u32 _reserved_2:8;
	};
};

-jx

Re: union/struct representations for MAS Registers

[Kumar Gala]

On Aug 10, 2011, at 12:21 PM, Jimi Xenidis wrote:

> I have some and use them in some code, they represent ISA 2.06 MAVN=3D1 =
(version 2)
> Can I keep them?
> if so, should I put them somewhere useful to others?
>=20
> Examples:
> union mas1 {
> 	u32 _val;
> 	struct {
> 		u32 v:1;
> 		u32 iprot:1;
> 		u32 tid:14;
> 		u32 _reserved_1:2;
> 		u32 ind:1;
> 		u32 ts:1;
> 		u32 tsize:4;
> 		u32 _reserved_2:8;
> 	};
> };

Uugh, we really have avoided unions for such things and it would be nice =
to keep it that way.

- k=

Re: union/struct representations for MAS Registers

[Jimi Xenidis]

On Aug 10, 2011, at 12:25 PM, Kumar Gala wrote:

>=20
> On Aug 10, 2011, at 12:21 PM, Jimi Xenidis wrote:
>=20
>> I have some and use them in some code, they represent ISA 2.06 MAVN=3D1=
 (version 2)
>> Can I keep them?
>> if so, should I put them somewhere useful to others?
>>=20
>> Examples:
>> union mas1 {
>> 	u32 _val;
>> 	struct {
>> 		u32 v:1;
>> 		u32 iprot:1;
>> 		u32 tid:14;
>> 		u32 _reserved_1:2;
>> 		u32 ind:1;
>> 		u32 ts:1;
>> 		u32 tsize:4;
>> 		u32 _reserved_2:8;
>> 	};
>> };
>=20
> Uugh, we really have avoided unions for such things and it would be =
nice to keep it that way.

I like "nice", I'll convert
-JX


>=20
> - k

RE: union/struct representations for MAS Registers

[David Laight]

=20
> I have some and use them in some code, they represent ISA=20
> 2.06 MAVN=3D1 (version 2)
> Can I keep them?
> if so, should I put them somewhere useful to others?
>=20
> Examples:
> union mas1 {
> 	u32 _val;
> 	struct {
> 		u32 v:1;
> 		u32 iprot:1;
> 		u32 tid:14;
> 		u32 _reserved_1:2;
> 		u32 ind:1;
> 		u32 ts:1;
> 		u32 tsize:4;
> 		u32 _reserved_2:8;
> 	};
> };

Bitfields are rather non-portable, the compiler has a lot of choice
about how to align the bits in memory.
Their use to map anything physical is doomed to portabilily issues.

	David

Re: union/struct representations for MAS Registers

[Jimi Xenidis]

On Aug 10, 2011, at 12:25 PM, David Laight wrote:

> 
>> I have some and use them in some code, they represent ISA 
>> 2.06 MAVN=1 (version 2)
>> Can I keep them?
>> if so, should I put them somewhere useful to others?
>> 
>> Examples:
>> union mas1 {
>> 	u32 _val;
>> 	struct {
>> 		u32 v:1;
>> 		u32 iprot:1;
>> 		u32 tid:14;
>> 		u32 _reserved_1:2;
>> 		u32 ind:1;
>> 		u32 ts:1;
>> 		u32 tsize:4;
>> 		u32 _reserved_2:8;
>> 	};
>> };
> 
> Bitfields are rather non-portable, the compiler has a lot of choice
> about how to align the bits in memory.

I'm ok with the masking stuff.
However, I'm actually surprised this is true given the maturity of our ABIs.

-JX
> Their use to map anything physical is doomed to portabilily issues.
> 
> 	David
> 
> 

RE: union/struct representations for MAS Registers

[David Laight]

=20
> > Bitfields are rather non-portable, the compiler has a lot of choice
> > about how to align the bits in memory.
>=20
> I'm ok with the masking stuff.
> However, I'm actually surprised this is true given the=20
> maturity of our ABIs.

The C standard says nothing at all about how bitfields are implemented,
I think the first bit might be 0x1, 0x80, 0x1000000 or 0x80000000
when treated as a 32bit value, regardless of the endianness.

Different architectures can (and do) assign things in different ways.
So code that is ok on ppc might fail on arm or x86 (etc).

	David

Re: union/struct representations for MAS Registers

[Kumar Gala]

On Aug 10, 2011, at 12:38 PM, David Laight wrote:

>=20
>>> Bitfields are rather non-portable, the compiler has a lot of choice
>>> about how to align the bits in memory.
>>=20
>> I'm ok with the masking stuff.
>> However, I'm actually surprised this is true given the=20
>> maturity of our ABIs.
>=20
> The C standard says nothing at all about how bitfields are =
implemented,
> I think the first bit might be 0x1, 0x80, 0x1000000 or 0x80000000
> when treated as a 32bit value, regardless of the endianness.
>=20
> Different architectures can (and do) assign things in different ways.
> So code that is ok on ppc might fail on arm or x86 (etc).
>=20
> 	David

I think PPCs a bit sane and what Jimi was proposing the union for is =
something that would never need to be portable (as it a PPC specific =
register).

Still, prefer the shifts, masks & macros as that's what I've been =
reading & using in ppc land forever ;)

- k=