Re: possible regression caused by "clocksource: sh_tmu: Set cpu_possible_mask to fix SMP broadcast"

[Simon Horman <horms@verge.net.au>]

On Wed, Jun 17, 2015 at 04:51:07PM +0900, Magnus Damm wrote:
> Hi Geert,
> 
> On Wed, Jun 17, 2015 at 4:45 PM, Geert Uytterhoeven
> <geert@linux-m68k.org> wrote:
> > On Wed, Jun 17, 2015 at 8:52 AM, Magnus Damm <magnus.damm@gmail.com> wrote:
> >> On Wed, Jun 17, 2015 at 11:48 AM, Simon Horman <horms@verge.net.au> wrote:
> >>> I have observed what appears to be a regression caused by
> >>> f2a5473861cf ("clocksource: sh_tmu: Set cpu_possible_mask to fix SMP
> >>> broadcast"), which was included in v3.19.
> >>>
> >>> The problem I see is that with a kernel compiled using marzen_defconfig on
> >>> the r8a7779/marzen board: i.e. a "legacy" kernel.
> >>>
> >>> The problem does not manifest when booting the same board using
> >>> a kernel built with shmobile_defconfig: i.e. a multiplatform kernel.
> >>>
> >>> It does not appear to affect other boards I have access to:
> >>> emev2/kzm9d, r7s72100/genmai, r8a73a4/ape6evm, r8a7740/armadillo900eva,
> >>> r8a77798/bockw r8a7790/lager r8a7791/koelsch, r8a7794/alt, sh73a0/kzm9g.
> >>>
> >>> I have observed this problem on the renesas-devel-20150617-v4.1-rc8
> >>> tag of my renesas tree. But I do not believe it is exclusive to that tag.
> >>>
> >>> The problem appears to be that there is no clocksource available during
> >>> early boot. The boot log at the end of the email was obtained by
> >>> enabling DEBUG_LL and earlyprintk.
> >>
> >> Thanks for reporting this. I suspect that the reason why this triggers
> >> on legacy is that we i such case most likely don't have TWD together
> >> with CCF. Since this is just old legacy code and the multiplatform
> >
> > We do have other A9 SMP SoCs (sh73a0, r8a7778).
> >
> > r8a7779.dtsi has an "arm,cortex-a9-twd-timer" node. r8a7778 hasn't.
> 
> Right, r8a7778 is not SMP so I don't think there is any TWD there. Or
> at least the Linux driver did not use to support running in UP mode.
> 
> > sh73a0 also has it, but see http://www.spinics.net/lists/linux-sh/msg39128.html
> > As bockw and marzen still have -reference variants, it may be more
> > difficult to fix.
> 
> Your TWD DT node is nicely pointing out the clock via CCF. On legacy
> this is most likely not possible, so we end up with trying to
> automatically determining the clock by assuming another clock is
> running. At least it used to be like that.
> 
> >> version should be equivalent I suggest that the correct approach is to
> >> use multiplatform support instead of legacy. And legacy r8a7779
> >> support should be removed right away if it hasn't already.
> >
> > Please wait, so I don't have to rebase the sh73a0/r8a7740 patches I'm
> > about to send out ;-)
> 
> Sure, please push out so we can clean up. =)

I'm happy to proceed with an orderly removal of marzen legacy
as a resolution to this problem.