Re: [PATCH v2 23/29] arm_mpam: Add mpam_msmon_read() to read monitor value

Ben Horgan
2025-09-11T15:46:39Z

Hi James,

On 9/10/25 21:43, James Morse wrote:
> Reading a monitor involves configuring what you want to monitor, and
> reading the value. Components made up of multiple MSC may need values
> from each MSC. MSCs may take time to configure, returning 'not ready'.
> The maximum 'not ready' time should have been provided by firmware.
>
> Add mpam_msmon_read() to hide all this. If (one of) the MSC returns
> not ready, then wait the full timeout value before trying again.
>
> CC: Shanker Donthineni <sdonthineni@nvidia.com>
> Signed-off-by: James Morse <james.morse@arm.com>
> ---
> Changes since v1:
> * Added XCL support.
> * Merged FLT/CTL constants.
> * a spelling mistake in a comment.
> * moved structrues around.
> ---
> drivers/resctrl/mpam_devices.c | 226 ++++++++++++++++++++++++++++++++
> drivers/resctrl/mpam_internal.h | 19 +++
> 2 files changed, 245 insertions(+)
>
> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
> index cf190f896de1..1543c33c5d6a 100644
> --- a/drivers/resctrl/mpam_devices.c
> +++ b/drivers/resctrl/mpam_devices.c
> @@ -898,6 +898,232 @@ static int mpam_msc_hw_probe(struct mpam_msc *msc)
> return 0;
> }
>
> +struct mon_read {
> + struct mpam_msc_ris *ris;
> + struct mon_cfg *ctx;
> + enum mpam_device_features type;
> + u64 *val;
> + int err;
> +};
> +
> +static void gen_msmon_ctl_flt_vals(struct mon_read *m, u32 *ctl_val,
> + u32 *flt_val)
> +{
> + struct mon_cfg *ctx = m->ctx;
> +
> + /*
> + * For CSU counters its implementation-defined what happens when not
> + * filtering by partid.
> + */
> + *ctl_val |= MSMON_CFG_x_CTL_MATCH_PARTID;
> +
> + *flt_val = FIELD_PREP(MSMON_CFG_x_FLT_PARTID, ctx->partid);
> + if (m->ctx->match_pmg) {
> + *ctl_val |= MSMON_CFG_x_CTL_MATCH_PMG;
> + *flt_val |= FIELD_PREP(MSMON_CFG_x_FLT_PMG, ctx->pmg);
> + }
> +
> + switch (m->type) {
> + case mpam_feat_msmon_csu:
> + *ctl_val = MSMON_CFG_CSU_CTL_TYPE_CSU;
> +
> + if (mpam_has_feature(mpam_feat_msmon_csu_xcl, &m->ris->props))
> + *flt_val |= FIELD_PREP(MSMON_CFG_CSU_FLT_XCL,
> + ctx->csu_exclude_clean);
> +
> + break;
> + case mpam_feat_msmon_mbwu:
> + *ctl_val = MSMON_CFG_MBWU_CTL_TYPE_MBWU;
> +
> + if (mpam_has_feature(mpam_feat_msmon_mbwu_rwbw, &m->ris->props))
> + *flt_val |= FIELD_PREP(MSMON_CFG_MBWU_FLT_RWBW, ctx->opts);
> +
> + break;
> + default:
> + return;
> + }
> +}
> +
> +static void read_msmon_ctl_flt_vals(struct mon_read *m, u32 *ctl_val,
> + u32 *flt_val)
> +{
> + struct mpam_msc *msc = m->ris->vmsc->msc;
> +
> + switch (m->type) {
> + case mpam_feat_msmon_csu:
> + *ctl_val = mpam_read_monsel_reg(msc, CFG_CSU_CTL);
> + *flt_val = mpam_read_monsel_reg(msc, CFG_CSU_FLT);
> + break;
> + case mpam_feat_msmon_mbwu:
> + *ctl_val = mpam_read_monsel_reg(msc, CFG_MBWU_CTL);
> + *flt_val = mpam_read_monsel_reg(msc, CFG_MBWU_FLT);
> + break;
> + default:
> + return;
> + }
> +}
> +
> +/* Remove values set by the hardware to prevent apparent mismatches. */
> +static void clean_msmon_ctl_val(u32 *cur_ctl)
> +{
> + *cur_ctl &= ~MSMON_CFG_x_CTL_OFLOW_STATUS;
> +}
> +
> +static void write_msmon_ctl_flt_vals(struct mon_read *m, u32 ctl_val,
> + u32 flt_val)
> +{
> + struct mpam_msc *msc = m->ris->vmsc->msc;
> +
> + /*
> + * Write the ctl_val with the enable bit cleared, reset the counter,
> + * then enable counter.
> + */
> + switch (m->type) {
> + case mpam_feat_msmon_csu:
> + mpam_write_monsel_reg(msc, CFG_CSU_FLT, flt_val);
> + mpam_write_monsel_reg(msc, CFG_CSU_CTL, ctl_val);
> + mpam_write_monsel_reg(msc, CSU, 0);
> + mpam_write_monsel_reg(msc, CFG_CSU_CTL, ctl_val | MSMON_CFG_x_CTL_EN);
> + break;
> + case mpam_feat_msmon_mbwu:
> + mpam_write_monsel_reg(msc, CFG_MBWU_FLT, flt_val);
> + mpam_write_monsel_reg(msc, CFG_MBWU_CTL, ctl_val);
> + mpam_write_monsel_reg(msc, MBWU, 0);
> + mpam_write_monsel_reg(msc, CFG_MBWU_CTL, ctl_val | MSMON_CFG_x_CTL_EN);
> + break;
> + default:
> + return;
> + }
> +}
> +
> +/* Call with MSC lock held */
> +static void __ris_msmon_read(void *arg)
> +{
> + u64 now;
> + bool nrdy = false;
> + struct mon_read *m = arg;
> + struct mon_cfg *ctx = m->ctx;
> + struct mpam_msc_ris *ris = m->ris;
> + struct mpam_props *rprops = &ris->props;
> + struct mpam_msc *msc = m->ris->vmsc->msc;
> + u32 mon_sel, ctl_val, flt_val, cur_ctl, cur_flt;
> +
> + if (!mpam_mon_sel_lock(msc)) {
> + m->err = -EIO;
> + return;
> + }
> + mon_sel = FIELD_PREP(MSMON_CFG_MON_SEL_MON_SEL, ctx->mon) |
> + FIELD_PREP(MSMON_CFG_MON_SEL_RIS, ris->ris_idx);
> + mpam_write_monsel_reg(msc, CFG_MON_SEL, mon_sel);
> +
> + /*
> + * Read the existing configuration to avoid re-writing the same values.
> + * This saves waiting for 'nrdy' on subsequent reads.
> + */
> + read_msmon_ctl_flt_vals(m, &cur_ctl, &cur_flt);
> + clean_msmon_ctl_val(&cur_ctl);
> + gen_msmon_ctl_flt_vals(m, &ctl_val, &flt_val);
> + if (cur_flt != flt_val || cur_ctl != (ctl_val | MSMON_CFG_x_CTL_EN))
> + write_msmon_ctl_flt_vals(m, ctl_val, flt_val);
> +
> + switch (m->type) {
> + case mpam_feat_msmon_csu:
> + now = mpam_read_monsel_reg(msc, CSU);
> + if (mpam_has_feature(mpam_feat_msmon_csu_hw_nrdy, rprops))
> + nrdy = now & MSMON___NRDY;
> + break;
> + case mpam_feat_msmon_mbwu:
> + now = mpam_read_monsel_reg(msc, MBWU);
> + if (mpam_has_feature(mpam_feat_msmon_mbwu_hw_nrdy, rprops))
> + nrdy = now & MSMON___NRDY;
> + break;
> + default:
> + m->err = -EINVAL;
> + break;
> + }
> + mpam_mon_sel_unlock(msc);
> +
> + if (nrdy) {
> + m->err = -EBUSY;
> + return;
> + }
> +
> + now = FIELD_GET(MSMON___VALUE, now);
> + *m->val += now;
> +}
> +
> +static int _msmon_read(struct mpam_component *comp, struct mon_read *arg)
> +{
> + int err, idx;
> + struct mpam_msc *msc;
> + struct mpam_vmsc *vmsc;
> + struct mpam_msc_ris *ris;
> +
> + idx = srcu_read_lock(&mpam_srcu);
> + list_for_each_entry_rcu(vmsc, &comp->vmsc, comp_list) {

This can be list_for_each_entry_srcu(). (I thought I'd already commented
but turns out that was on another patch.)

> + msc = vmsc->msc;
> +
> + list_for_each_entry_rcu(ris, &vmsc->ris, vmsc_list) {

Also here.

[...]

Thanks,

Ben