On 15 January 2011 16:11, Russell King - ARM Linux
<li...@arm.linux.org.uk> wrote:
> SMP requires at least the ARMv6K extensions to be present, so if we're
> running on SMP, the WFE and SEV instructions must be available.
>
> However, when we run on UP, the v6K extensions may not be available,
> and so we don't want WFE/SEV to be in the instruction stream. Use the
> SMP alternatives infrastructure to replace these instructions with NOPs
> if we build for SMP but run on UP.
[...]
> --- a/arch/arm/include/asm/spinlock.h
> +++ b/arch/arm/include/asm/spinlock.h
> @@ -5,17 +5,36 @@
> #error SMP not supported on pre-ARMv6 CPUs
> #endif
>
> +/*
> + * sev and wfe are ARMv6K extensions. Uniprocessor ARMv6 may not have the K
> + * extensions, so when running on UP, we have to patch these instructions
> away.
> + */
> +#define ALT_SMP(smp, up) \
> + "9998: " smp "\n" \
> + " .pushsection \".alt.smp.init\", \"a\"\n" \
> + " .long 9998b\n" \
> + " " up "\n" \
> + " .popsection\n"
> +
> +#ifdef CONFIG_THUMB2_KERNEL
> +#define SEV ALT_SMP("sev.w", "nop.w")
> +#define WFE(cond) ALT_SMP("wfe" cond ".w", "nop.w")
> +#else
> +#define SEV ALT_SMP("sev", "nop")
> +#define WFE(cond) ALT_SMP("wfe" cond, "nop")
> +#endif
In the SEV macro definition, can you also include the dsb? This
barrier is only there because of sev, otherwise we don't need it (we
have a dmb prior to releasing the lock).
--
Catalin
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