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

[Nikhil Kumar Singh <nikhilks@linux.ibm.com>]

Hi Mukesh,

Ideally, checkpatch should take care of this, I see no checkpatch errors.

```
./scripts/checkpatch.pl 
v2-0001-powerpc-64s-Clarify-copy_and_flush-cache-sync-loo.patch
total: 0 errors, 0 warnings, 26 lines checked

v2-0001-powerpc-64s-Clarify-copy_and_flush-cache-sync-loo.patch has no 
obvious style problems and is ready for submission.
```

Thanks
~ Nikhil

On 07/07/26 12:48, 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
>
> 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@linux.ibm.com>
>>> ---
>>>   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
>>>