Re: [PATCH] powerpc/64s: Clarify copy_and_flush() cache sync loop comment

[Mahesh J Salgaonkar]

On 2026-07-01 23:57:56 Wed, Nikhil Kumar Singh wrote:
> The value loaded into r0 in copy_and_flush() represents the number of
> 8-byte words processed between cache synchronization operations.
> 
> The existing comment refers to cache line size, which can make it appear
> that the value is a cache line size in bytes rather than a loop count.
> Clarify the comment to explain that the loop processes 8 words (64 bytes)
> per cache synchronization iteration, and that increasing the value would
> skip cache maintenance for intermediate cache lines.
> 
> This is a comment-only change with no functional impact.
> 
> Signed-off-by: Nikhil Kumar Singh <nikhilks@xxxxxxxxxxxxx>
> ---
>  arch/powerpc/kernel/head_64.S | 16 ++++++++--------
>  1 file changed, 8 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S
> index 63432a33ec49..e21c2bce8f7e 100644
> --- a/arch/powerpc/kernel/head_64.S
> +++ b/arch/powerpc/kernel/head_64.S
> @@ -713,14 +713,14 @@ p_end: .8byte _end - copy_to_here
>  _GLOBAL(copy_and_flush)
>  	addi	r5,r5,-8
>  	addi	r6,r6,-8
> -4:	li	r0,8			/* Use the smallest common	*/
> -					/* denominator cache line	*/
> -					/* size.  This results in	*/
> -					/* extra cache line flushes	*/
> -					/* but operation is correct.	*/
> -					/* Can't get cache line size	*/
> -					/* from NACA as it is being	*/
> -					/* moved too.			*/
> +4:	li	r0,8			/* r0 is the number of 8-byte words       */
> +					/* to copy per cache sync iteration.      */
> +					/* 8 words * 8 bytes = 64 bytes. 64B is   */
> +					/* the current default cache line size.   */
> +					/* This is a loop count, not a byte       */
> +					/* count. Increasing it will skip         */
> +					/* dcbst/icbi for lines in between and    */
> +					/* leave stale instructions in icache.    */

Looks good to me. The previous comment was misleading which makes one to
think r0 as cache line size which is not the case.

Reviewed-by: Mahesh Salgaonkar <mahesh@xxxxxxxxxxxxx>

Thanks,
-Mahesh.