[Etherboot-users] Re: Via RNG xstore in Etherboot

[Robert H. <rob...@ya...>]

I've figured it out after paying closer attention to
the Via padlock programmers guide!

If I set bit 9 on CR4 using the following bit of
assembly (from the Linux kernel) it works. Something
to do with a dependency on the SSE instructions,
according to the docs.

static inline void set_in_cr4 (unsigned long mask)
{
    __asm__("movl %%cr4,%%eax\n\t"
        "orl %0,%%eax\n\t"
        "movl %%eax,%%cr4\n"
        : : "irg" (mask)
        :"ax");
}

and call with:

set_in_cr4( 0x0200 );

Hope the info is useful to someone!

Robert

> BTW the processor is a VIA Eden, with Nehemiah core
> (stepping 8), and the xstore call works once the
> Linux
> kernel is up and running - so I know that it can
> work...
> 
> --- Robert Hamilton <rob...@ya...>
> wrote:
> 
> > Hi all,
> > 
> > OK this question may be a bit obscure, but I hope
> > someone might have some insight as to what is
> going
> > on...
> > 
> > I am trying to call the Via RNG (xstore
> instruction)
> > from etherboot, and my platform resets every time
> I
> > call it.
> > 
> > I have copied the xstore asm() code from the
> > hw_random.c driver in Linux. I have made sure the
> > Via
> > MSR 0x110b is set up correctly. I've checked that
> > the
> > assembler and byte code looks OK (the same as the
> > hwrandom driver), but I still get the reset.
> > 
> > Do I have to set something else up on the
> processor,
> > or call xstore in a different way?
> > 
> > Thanks,
> > 
> > Robert
> > 
> > The following is the code I am using showing the
> MSR
> > initialization and the xstore call. Though the
> first
> > read of the MSR indicates that the RNG is enabled
> by
> > default anyway. It is pretty much a straight copy
> > from
> > hw_random.c.
> > 
> > #define MSR_VIA_RNG 0x110b
> > enum {
> >     VIA_STRFILT_CNT_SHIFT = 16,
> >     VIA_STRFILT_FAIL = (1 << 15),
> >     VIA_STRFILT_ENABLE = (1 << 14),
> >     VIA_RAWBITS_ENABLE = (1 << 13),
> >     VIA_RNG_ENABLE = (1 << 6),
> >     VIA_XSTORE_CNT_MASK = 0x0F,
> > 
> >     VIA_RNG_CHUNK_8 = 0x00, /* 64 rand bits, 64
> > stored
> > bits */
> >     VIA_RNG_CHUNK_4 = 0x01, /* 32 rand bits, 32
> > stored
> > bits */
> >     VIA_RNG_CHUNK_4_MASK = 0xFFFFFFFF,
> >     VIA_RNG_CHUNK_2 = 0x02, /* 16 rand bits, 32
> > stored
> > bits */
> >     VIA_RNG_CHUNK_2_MASK = 0xFFFF,
> >     VIA_RNG_CHUNK_1 = 0x03, /* 8 rand bits, 32
> > stored
> > bits */
> > 
> >     VIA_RNG_CHUNK_1_MASK = 0xFF,
> > };
> > 
> > #define rdmsr(msr,val1,val2) \
> >     __asm__ __volatile__("rdmsr" \
> >         : "=a" (val1), "=d" (val2) \
> >         : "c" (msr))
> > 
> > #define wrmsr(msr,val1,val2) \
> >     __asm__ __volatile__("wrmsr" \
> >         : /* no outputs */ \
> >         : "c" (msr), "a" (val1), "d" (val2))
> > 
> > static int via_RNGinit( void )
> > {
> >     u32 lo, hi, old_lo;
> > 
> >     printf( "VIA init\n" );
> >     rdmsr(MSR_VIA_RNG, lo, hi);
> >     printf( "lo = %#x, hi = %#x\n", lo, hi );
> > 
> >     old_lo = lo;
> >     lo &= ~(0x7f << VIA_STRFILT_CNT_SHIFT);
> >     lo &= ~VIA_XSTORE_CNT_MASK;
> >     lo |= (VIA_STRFILT_ENABLE | VIA_STRFILT_FAIL |
> > VIA_RAWBITS_ENABLE);
> >     lo |= VIA_RNG_ENABLE;
> >     lo |= ( 0x3 << 8 );
> > 
> >     if (lo != old_lo)
> >         wrmsr(MSR_VIA_RNG, lo, hi);
> > 
> >     rdmsr(MSR_VIA_RNG, lo, hi);
> >     printf( "lo = %#x, hi = %#x\n", lo, hi );
> >     if ((lo & VIA_RNG_ENABLE) == 0) {
> >         printf( "cannot enable VIA C3 RNG,
> > aborting\n");
> >         return -1;
> >     }
> > 
> >     printf( "Done!\n" );
> > 
> >     return 0;
> > }
> > 
> > static inline u32 xstore(u32 *addr, u32 edx_in)
> > {
> >     u32 eax_out;
> > 
> >     asm volatile (".byte 0x0f,0xa7,0xc0 /* xstore
> > %%edi (addr=%0) */"
> >         : "=a"(eax_out), "=m"(*addr)
> >         : "D"(addr), "d"(edx_in));
> > 
> >     return eax_out;
> > }
> > 
> > 
> > 
> > 		
> > __________________________________________ 
> > Yahoo! DSL – Something to write home about. 
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> > 
> > 
> 
> 
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