Re: [PATCH 3/3] perf/arm-cmn: Enable support for tertiary match group

Robin Murphy
2024-01-29T17:07:49Z

On 2024-01-26 10:12 pm, Ilkka Koskinen wrote:
> Add support for tertiary match group.
>
> Signed-off-by: Ilkka Koskinen <ilkka@os.amperecomputing.com>
> ---
> drivers/perf/arm-cmn.c | 23 +++++++++++++++++++----
> 1 file changed, 19 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/perf/arm-cmn.c b/drivers/perf/arm-cmn.c
> index dc6370396ad0..ce9fbdcf6144 100644
> --- a/drivers/perf/arm-cmn.c
> +++ b/drivers/perf/arm-cmn.c
> @@ -91,10 +91,13 @@
> #define CMN600_WPn_CONFIG_WP_COMBINE BIT(6)
> #define CMN600_WPn_CONFIG_WP_EXCLUSIVE BIT(5)
> #define CMN_DTM_WPn_CONFIG_WP_GRP GENMASK_ULL(5, 4)
> +#define CMN600_WPn_CONFIG_WP_GRP BIT(4)
> #define CMN_DTM_WPn_CONFIG_WP_CHN_SEL GENMASK_ULL(3, 1)
> #define CMN_DTM_WPn_CONFIG_WP_DEV_SEL BIT(0)
> #define CMN_DTM_WPn_VAL(n) (CMN_DTM_WPn(n) + 0x08)
> #define CMN_DTM_WPn_MASK(n) (CMN_DTM_WPn(n) + 0x10)
> +#define CMN_DTM_WP_CHN_SEL_REQ_VC 0
> +#define CMN_DTM_WP_GRP_TERTIARY 0x2
>
> #define CMN_DTM_PMU_CONFIG 0x210
> #define CMN__PMEVCNT0_INPUT_SEL GENMASK_ULL(37, 32)
> @@ -175,8 +178,8 @@
> #define CMN_CONFIG_WP_DEV_SEL GENMASK_ULL(50, 48)
> #define CMN_CONFIG_WP_CHN_SEL GENMASK_ULL(55, 51)
> /* Note that we don't yet support the tertiary match group on newer IPs */
> -#define CMN_CONFIG_WP_GRP BIT_ULL(56)
> -#define CMN_CONFIG_WP_EXCLUSIVE BIT_ULL(57)
> +#define CMN_CONFIG_WP_GRP GENMASK_ULL(57, 56)
> +#define CMN_CONFIG_WP_EXCLUSIVE BIT_ULL(58)
> #define CMN_CONFIG1_WP_VAL GENMASK_ULL(63, 0)
> #define CMN_CONFIG2_WP_MASK GENMASK_ULL(63, 0)
>
> @@ -1298,7 +1301,9 @@ static struct attribute *arm_cmn_format_attrs[] = {
>
> CMN_FORMAT_ATTR(CMN_ANY, wp_dev_sel, CMN_CONFIG_WP_DEV_SEL),
> CMN_FORMAT_ATTR(CMN_ANY, wp_chn_sel, CMN_CONFIG_WP_CHN_SEL),
> - CMN_FORMAT_ATTR(CMN_ANY, wp_grp, CMN_CONFIG_WP_GRP),
> + CMN_FORMAT_ATTR(CMN600, wp_grp, CMN600_WPn_CONFIG_WP_GRP),

Perhaps an easy confusion, but 4 != 56: CMN_CONFIG_WP_* represent
perf_event->config{,1,2} attribute fields per the CMN_CONFIG_* pattern,
whereas CMN*_WPn_CONFIG_* are hardware register fields where "config" is
just annoygingly part of the register name.

> + CMN_FORMAT_ATTR(NOT_CMN600, wp_grp, CMN_CONFIG_WP_GRP),

Hmm, I'm sure last time I tried something like this, sysfs wouldn't let
two attributes with the same name exist, regardless of whether one was
meant to be hidden :/

TBH I think that either we change ABI for everyone consistently, or we
extend the field in a backwards-compatible way. If you think an ABI
break would affect existing CMN-600 users, then surely at stands to
affect existing CMN-650 and CMN-700 users just as much?

> +
> CMN_FORMAT_ATTR(CMN_ANY, wp_exclusive, CMN_CONFIG_WP_EXCLUSIVE),
> CMN_FORMAT_ATTR(CMN_ANY, wp_combine, CMN_CONFIG_WP_COMBINE),
>
> @@ -1398,8 +1403,11 @@ static u32 arm_cmn_wp_config(struct perf_event *event)
>
> config = FIELD_PREP(CMN_DTM_WPn_CONFIG_WP_DEV_SEL, dev) |
> FIELD_PREP(CMN_DTM_WPn_CONFIG_WP_CHN_SEL, chn) |
> - FIELD_PREP(CMN_DTM_WPn_CONFIG_WP_GRP, grp) |
> FIELD_PREP(CMN_DTM_WPn_CONFIG_WP_DEV_SEL2, dev >> 1);
> +
> + if (grp)
> + config |= is_cmn600 ? CMN600_WPn_CONFIG_WP_GRP :
> + FIELD_PREP(CMN_DTM_WPn_CONFIG_WP_GRP, grp);

FWIW I think something more like "if (is_cmn600) grp &= 1;" before the
existing assignent might be clearer. Note that that *is* effectively how
this works already since CMN_DTM_WPn_CONFIG_WP_GRP was updated, it's
just currently implicit in CMN_EVENT_WP_GRP().

> if (exc)
> config |= is_cmn600 ? CMN600_WPn_CONFIG_WP_EXCLUSIVE :
> CMN_DTM_WPn_CONFIG_WP_EXCLUSIVE;

You've missed the "(combine && !grp)" logic below this point, which also
needs to get rather more involved if a combined match across groups 1
and 2 is going to work correctly.

> @@ -1764,6 +1772,13 @@ static int arm_cmn_event_init(struct perf_event *event)
> /* ...and we need a "real" direction */
> if (eventid != CMN_WP_UP && eventid != CMN_WP_DOWN)
> return -EINVAL;
> +
> + if (cmn->part != PART_CMN600)
> + if (CMN_EVENT_WP_GRP(event) > CMN_DTM_WP_GRP_TERTIARY ||
> + (CMN_EVENT_WP_GRP(event) == CMN_DTM_WP_GRP_TERTIARY &&
> + CMN_EVENT_WP_CHN_SEL(event) != CMN_DTM_WP_CHN_SEL_REQ_VC))
> + return -EINVAL;
> +

We already don't attempt to sanity-check watchpoint arguments (e.g.
chn>3 or chn=1,grp=1), so I'm not really inclined to start. The aim here
has always been not to try to understand watchpoints at all, and
effectively just pass through the register interface to the user.

Thanks,
Robin.

> /* ...but the DTM may depend on which port we're watching */
> if (cmn->multi_dtm)
> hw->dtm_offset = CMN_EVENT_WP_DEV_SEL(event) / 2;