Re: [Fwd: [bug report] 0xffffffffc0000000 can't be used on bcm1250]

[Ralf Baechle <ralf@linux-mips.org>]

On Mon, Oct 13, 2008 at 04:18:04PM +0100, Maciej W. Rozycki wrote:

>  /*
> + * To avoid the BCM1250 M3 erratum check whether EntryHi is consistent
> + * with BadVAddr and return for the exception to retrigger if not.
> + */
> +static void __cpuinit build_bcm1250_m3_war(u32 **p, struct uasm_reloc **r)
> +{
> +	uasm_i_dmfc0(p, K0, C0_BADVADDR);
> +	uasm_i_dmfc0(p, K1, C0_ENTRYHI);
> +	uasm_i_xor(p, K0, K0, K1);
> +	uasm_i_dsll(p, K1, K0, 24);
> +	uasm_i_dsrl32(p, K1, K1, (24 + PAGE_SHIFT + 1) - 32);
> +	uasm_i_dsrl32(p, K0, K0, 30);
> +	uasm_i_or(p, K0, K0, K1);
> +	uasm_il_bnez(p, r, K0, label_leave);

The workaround is beginning to be relativly expensive.  We're investing 8
instructions extra only to verify that the content of c0_entryhi is
correct.  I haven't tried yet but me seems by avoiding the use of c0_context
entirely relying only on badvaddr we may be able to get away cheaper.

Btw, adding linux-mips to the cc list.  This really should be public.

  Ralf