On Tue, Dec 24, 2024 at 10:44:08AM +0000, James Clark wrote:
> FEAT_SPEv1p2 (optional from Armv8.6) adds a discard mode that allows all
> SPE data to be discarded rather than written to memory. Add a format
> bit for this mode.
>
> If the mode isn't supported, the format bit isn't published and attempts
> to use it will result in -EOPNOTSUPP. Allocating an aux buffer is still
> allowed even though it won't be written to so that old tools continue to
> work, but updated tools can choose to skip this step.
>
> Reviewed-by: Yeoreum Yun <yeoreum.yun@xxxxxxx>
> Signed-off-by: James Clark <james.clark@xxxxxxxxxx>
> ---
> drivers/perf/arm_spe_pmu.c | 23 +++++++++++++++++++++++
> 1 file changed, 23 insertions(+)
>
> diff --git a/drivers/perf/arm_spe_pmu.c b/drivers/perf/arm_spe_pmu.c
> index fd5b78732603..9aaf3f98e6f5 100644
> --- a/drivers/perf/arm_spe_pmu.c
> +++ b/drivers/perf/arm_spe_pmu.c
> @@ -193,6 +193,9 @@ static const struct attribute_group arm_spe_pmu_cap_group = {
> #define ATTR_CFG_FLD_store_filter_CFG config /* PMSFCR_EL1.ST */
> #define ATTR_CFG_FLD_store_filter_LO 34
> #define ATTR_CFG_FLD_store_filter_HI 34
> +#define ATTR_CFG_FLD_discard_CFG config /* PMBLIMITR_EL1.FM = DISCARD */
> +#define ATTR_CFG_FLD_discard_LO 35
> +#define ATTR_CFG_FLD_discard_HI 35
>
> #define ATTR_CFG_FLD_event_filter_CFG config1 /* PMSEVFR_EL1 */
> #define ATTR_CFG_FLD_event_filter_LO 0
> @@ -216,6 +219,7 @@ GEN_PMU_FORMAT_ATTR(store_filter);
> GEN_PMU_FORMAT_ATTR(event_filter);
> GEN_PMU_FORMAT_ATTR(inv_event_filter);
> GEN_PMU_FORMAT_ATTR(min_latency);
> +GEN_PMU_FORMAT_ATTR(discard);
>
> static struct attribute *arm_spe_pmu_formats_attr[] = {
> &format_attr_ts_enable.attr,
> @@ -228,9 +232,15 @@ static struct attribute *arm_spe_pmu_formats_attr[] = {
> &format_attr_event_filter.attr,
> &format_attr_inv_event_filter.attr,
> &format_attr_min_latency.attr,
> + &format_attr_discard.attr,
> NULL,
> };
>
> +static bool discard_unsupported(struct arm_spe_pmu *spe_pmu)
> +{
> + return spe_pmu->pmsver < ID_AA64DFR0_EL1_PMSVer_V1P2;
> +}
Why not add a new SPE_PMU_FEAT_* for this and handle it in a similar
way to other optional hardware features?
Will
