[U-Boot] tlbentry for U3 bit

[U-Boot] tlbentry for U3 bit

[Ronny D]

I am using ppc440 based board. I have
added one tlbentry in init.S for memctrl register with U3 bit enable.

When I check the tlb entry through
BDI I found that U3 bit is disabled.

?

I have done the same thing using
change_tlb then I have seen U3 bit enabled through BDI.

?

Please let me know

Is there any limitation of init.S
for setting tlbenty with U3 bit enable?
-Ronny




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[U-Boot] tlbentry for U3 bit

[Stefan Roese]

Hi Ronny,

On Monday 19 April 2010 12:42:29 Ronny D wrote:
> I am using ppc440 based board. I have
> added one tlbentry in init.S for memctrl register with U3 bit enable.
> 
> When I check the tlb entry through
> BDI I found that U3 bit is disabled.
> 
> I have done the same thing using
> change_tlb then I have seen U3 bit enabled through BDI.
> 
> Please let me know
> 
> Is there any limitation of initS
> for setting tlbenty with U3 bit enable?

Take a look at the "tlbentry" macro (arch/ppc/include/mmu.h). As you can see, 
the TLB2 macro does not allow changing any of the Ux bits:

#define tlbentry(epn,sz,rpn,erpn,attr)\
	.long TLB0(epn,sz),TLB1(rpn,erpn),TLB2(attr)

#define TLB2(a)		((a) & 0x00000fbf)

So you need to change TLB2 if you need to set those Ux bits.

BTW: The PPC440 users manual mentions that the U3 storage attribute has no 
effect on PPC440. So I'm wondering what you are trying to achieve by setting 
this bit.

Cheers,
Stefan

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