Re: [PATCH 2/2] eal/riscv: add support for zicbop extension

[Daniel Gregory <daniel.gregory@bytedance.com>]

On Thu, May 30, 2024 at 06:19:48PM +0100, Daniel Gregory wrote:
> + * The RTE_RISCV_ZICBOP option controls whether we emit them manually for older
> + * compilers that may not have the support to assemble them.
> + */
>  static inline void rte_prefetch0(const volatile void *p)
>  {
> -	RTE_SET_USED(p);
> +#ifndef RTE_RISCV_ZICBOP
> +	/* by default __builtin_prefetch prepares for a read */
> +	__builtin_prefetch((const void *)p);

This cast causes warnings (which are treated as errors by the 0-day
Robot) due to it discarding the 'volatile' on p. 

Removing the volatile from the definition of rte_prefetch0 causes build
failures in some drivers (txgbe_rxtx.c:1809, ixgbe_rxtx.c:2174,
enic_rxtx.c:127, ...).

rte_prefetch0_write takes its argument as 'const void *' and so can use
__builtin_prefetch().