Re: [PATCH 7.1 667/744] ptp: ptp_s390: Add missing facility check

On Fri, Jul 31, 2026 at 10:18:54AM +0200, Sven Schnelle wrote:
> Greg Kroah-Hartman <[email protected]> writes:
> 
> > On Fri, Jul 31, 2026 at 08:21:26AM +0200, Jiri Slaby wrote:
> >> On 30. 07. 26, 16:15, Greg Kroah-Hartman wrote:
> >> > 7.1-stable review patch.  If anyone has any objections, please let me know.
> >> > 
> >> > ------------------
> >> > 
> >> > From: Sven Schnelle <[email protected]>
> >> > 
> >> > commit e78f1ac37afcb16cb6fef8a2c92591eab6558956 upstream.
> >> > 
> >> > Only register the physical clock when facility 28 is installed
> >> > and PTFF QAF returns that PTFF QPT is available.
> >> > 
> >> > Fixes: 2d7de7a3010d ("s390/time: Add PtP driver")
> >> > Signed-off-by: Sven Schnelle <[email protected]>
> >> > Cc: [email protected]
> >> > Reviewed-by: Heiko Carstens <[email protected]>
> >> > Link: https://patch.msgid.link/[email protected]
> >> > Signed-off-by: Jakub Kicinski <[email protected]>
> >> > Signed-off-by: Greg Kroah-Hartman <[email protected]>
> >> > ---
> >> >   drivers/ptp/ptp_s390.c |    6 +++++-
> >> >   1 file changed, 5 insertions(+), 1 deletion(-)
> >> > 
> >> > --- a/drivers/ptp/ptp_s390.c
> >> > +++ b/drivers/ptp/ptp_s390.c
> >> > @@ -107,6 +107,9 @@ static __init int ptp_s390_init(void)
> >> >   	if (IS_ERR(ptp_stcke_clock))
> >> >   		return PTR_ERR(ptp_stcke_clock);
> >> > +	if (!test_facility(28) || !ptff_query(PTFF_QPT))
> >> 
> >> ptff_query() here needs:
> >> 9de445d8296a ("s390/ptff: Export ptff_function_mask[]")
> >
> > Ah, good catch, now queued up.  How did you find that thing?
> 
> Maybe we should change the documentation. I was wondering whether I have
> to mark that as a dependency, looked up ./process/stable-kernel-rules.rst
> which says:
> 
>   Note that for a patch series, you do not have to list as prerequisites the
>   patches present in the series itself. For example, if you have the following
>   patch series::
> 
>     patch1
>     patch2
> 
>   where patch2 depends on patch1, you do not have to list patch1 as
>   prerequisite of patch2 if you have already marked patch1 for stable
>   inclusion.
> 
> Which lead me to believe that I don't have to add stable@ to the the
> other patch, but looks like this was wrong?

The issue is that was no link that I could find between 9de445d8296a
("s390/ptff: Export ptff_function_mask[]") and e78f1ac37afc ("ptp:
ptp_s390: Add missing facility check")

i.e. no "Fixes:" tag, or dependancy info, so if I took the "add
missing..." patch, I didn't know that the export patch was required.

Not a big deal, happens at times, just if you know a commit fixes an
older patch, a "Fixes:" tag is helpful.

thanks,

greg k-h