Subject: [PATCH] drivers/perf: hisi: update the sccl_id/ccl_id when MT is supported

From: [email-masked] (Will Deacon)
Date: Tue, 24 Jul 2018 15:39:29 +0100

On Tue, Jul 24, 2018 at 07:06:11PM +0800, Zhangshaokun wrote:
> On 2018/7/23 22:42, Will Deacon wrote:
> > On Thu, Jul 19, 2018 at 07:26:40PM +0800, Shaokun Zhang wrote:
> >> MT bit in MPIDR_EL1 is now supported in certain HiSilicon platforms, so
> >> the mapping between sccl_id/ccl_id and affinity level needs to be updated
> >> from the generic encoding we originally used.
> >>
> >> Cc: John Garry <[email-masked]>
> >> Cc: Will Deacon <[email-masked]>
> >> Cc: Mark Rutland <[email-masked]>
> >> Signed-off-by: Shaokun Zhang <[email-masked]>
> >> ---
> >>  drivers/perf/hisilicon/hisi_uncore_pmu.c | 13 ++++++++-----
> >>  1 file changed, 8 insertions(+), 5 deletions(-)
> >>
> >> diff --git a/drivers/perf/hisilicon/hisi_uncore_pmu.c b/drivers/perf/hisilicon/hisi_uncore_pmu.c
> >> index 44df613..b3c5ae9 100644
> >> --- a/drivers/perf/hisilicon/hisi_uncore_pmu.c
> >> +++ b/drivers/perf/hisilicon/hisi_uncore_pmu.c
> >> @@ -350,19 +350,22 @@ void hisi_uncore_pmu_disable(struct pmu *pmu)
> >>  
> >>  /*
> >>   * Read Super CPU cluster and CPU cluster ID from MPIDR_EL1.
> >> - * If multi-threading is supported, SCCL_ID is in MPIDR[aff3] and CCL_ID
> >> - * is in MPIDR[aff2]; if not, SCCL_ID is in MPIDR[aff2] and CCL_ID is
> >> - * in MPIDR[aff1]. If this changes in future, this shall be updated.
> >> + * If multi-threading is supported, CCL_ID is the low 3-bits in MPIDR[Aff2]
> >> + * and SCCL_ID is the upper 5-bits of Aff2 field; if not, SCCL_ID
> >> + * is in MPIDR[Aff2] and CCL_ID is in MPIDR[Aff1]. If this changes in
> >> + * future, this shall be updated.
> >>   */
> >>  static void hisi_read_sccl_and_ccl_id(int *sccl_id, int *ccl_id)
> >>  {
> >>  	u64 mpidr = read_cpuid_mpidr();
> >>  
> >>  	if (mpidr & MPIDR_MT_BITMASK) {
> > 
> > So, to be clear, you're saying that the MT bit was not set in any previous
> > SoC with this PMU, and therefore changing this logic doesn't introduce a
> > functional regression?
> > 
> 
> Yes, you are right. When the driver was developed, the MT bit was not supported
> and I was told that it may be set later in certain HiSilicon platform, therefore
> I checked this field in the code.
> Now the MT bit is set in one platform, but the mapping between sccl_id/ccl_id and
> affinity level is different from the origin encoding and needs to be updated.
> Of course, there is no functional regression.
> 
> > Assuming that's the case, and you now have an SoC with MT set, then I don't
> > think the comment above which says "If this changes in future, this shall be
> > updated" can be correct, because changing the mapping will regress an older
> > platform, won't it?
> > 
> 
> Agree, at the beginning, I am not sure about it in future. I will take this
> information to the SoC team and drop this comment in next version.

It's ok, I can drop the comment when I apply the patch.

Thanks,

Will