Re: [PATCH v2] powerpc/64s: Clarify copy_and_flush() cache sync loop comment

[Mukesh Kumar Chaurasiya]

On Tue, Jul 07, 2026 at 12:48:57PM +0530, Nikhil Kumar Singh wrote:
> Hi Mukesh,
> 
> Thanks for reviewing the patch and for the suggestion.
> I'd prefer to keep the current alignment as I find it a bit more readable.
> 
> Thanks,
> ~ Nikhil
> 
There is a reason we keep the character limit to 80 chars. Please go
through these coding guidelines.

https://docs.kernel.org/process/coding-style.html

Regards,
Mukesh

> On 07/07/26 11:08, Mukesh Kumar Chaurasiya wrote:
> > On Mon, Jul 06, 2026 at 01:57:08PM +0530, 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 | 20 ++++++++++++--------
> > >   1 file changed, 12 insertions(+), 8 deletions(-)
> > > 
> > > diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S
> > > index 63432a33ec49..a54f6f979173 100644
> > > --- a/arch/powerpc/kernel/head_64.S
> > > +++ b/arch/powerpc/kernel/head_64.S
> > > @@ -713,14 +713,18 @@ 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 may skip	*/
> > > +					/* dcbst/icbi for lines in between and	*/
> > > +					/* leave stale instructions in icache.	*/
> > > +					/* 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.		*/
> > The comment looks fine. But the alignement of the comment is still
> > different from earlier. Keep the alignment same as earlier, it looks a
> > little nicer.
> > 
> > Regards,
> > Mukesh
> > >   	mtctr	r0			/* put # words/line in ctr	*/
> > >   3:	addi	r6,r6,8			/* copy a cache line		*/
> > > -- 
> > > 2.43.5
> > > 
>