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

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

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;
> }
> 
> 
> 
> 		
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> 


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