[PATCH v2 05/11] arm64: sve: Provide a conditional update accessor for ZCR_ELx

[Mark Brown]

On Thu, Mar 18, 2021 at 12:25:26PM +0000, Marc Zyngier wrote:

> A common pattern is to conditionally update ZCR_ELx in order
> to avoid the "self-synchronizing" effect that writing to this
> register has.
> 
> Let's provide an accessor that does exactly this.

Reviewed-by: Mark Brown <broonie at kernel.org>

> +#define sve_cond_update_zcr_vq(val, reg)		\
> +	do {						\
> +		u64 __zcr = read_sysreg_s((reg));	\
> +		u64 __new = __zcr & ~ZCR_ELx_LEN_MASK;	\
> +		__new |= (val) & ZCR_ELx_LEN_MASK;	\
> +		if (__zcr != __new)			\
> +			write_sysreg_s(__new, (reg));	\
> +	} while (0)
> +

Do compilers actually do much better with this than with a static
inline like the other functions in this header?  Seems like something
they should be figuring out.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 488 bytes
Desc: not available
URL: <http://lists.infradead.org/pipermail/linux-arm-kernel/attachments/20210319/e0474dd2/attachment-0001.sig>