Re: [RFC PATCH 25/38] arm_mpam: resctrl: Add resctrl_arch_rmid_read() and resctrl_arch_reset_rmid()

Jonathan Cameron
2025-12-18T13:53:22Z

On Fri, 5 Dec 2025 21:58:48 +0000
James Morse <james.morse@arm.com> wrote:

> resctrl uses resctrl_arch_rmid_read() to read counters. CDP emulation
> means the counter may need reading in three different ways. The same
> goes for reset.
>
> The helpers behind the resctrl_arch_ functions will be re-used for the
> ABMC equivalent functions.
>
> Add the rounding helper for checking monitor values while we're here.
>
> Signed-off-by: James Morse <james.morse@arm.com>
> ---
> drivers/resctrl/mpam_resctrl.c | 154 +++++++++++++++++++++++++++++++++
> include/linux/arm_mpam.h | 5 ++
> 2 files changed, 159 insertions(+)
>
> diff --git a/drivers/resctrl/mpam_resctrl.c b/drivers/resctrl/mpam_resctrl.c
> index a2b238d47117..dc8a819d0976 100644
> --- a/drivers/resctrl/mpam_resctrl.c
> +++ b/drivers/resctrl/mpam_resctrl.c
> @@ -355,6 +355,160 @@ void resctrl_arch_mon_ctx_free(struct rdt_resource *r,
> resctrl_arch_mon_ctx_free_no_wait(evtid, mon_idx);
> }
>
> +static int
> +__read_mon(struct mpam_resctrl_mon *mon, struct mpam_component *mon_comp,
> + enum mpam_device_features mon_type,
> + int mon_idx,
> + enum resctrl_conf_type cdp_type, u32 closid, u32 rmid, u64 *val)
> +{
> + struct mon_cfg cfg = { };
> +
> + if (!mpam_is_enabled())
> + return -EINVAL;
> +
> + /* Shift closid to account for CDP */
> + closid = resctrl_get_config_index(closid, cdp_type);
> +
> + if (mon_idx == USE_PRE_ALLOCATED) {
> + int mbwu_idx = resctrl_arch_rmid_idx_encode(closid, rmid);
> + mon_idx = mon->mbwu_idx_to_mon[mbwu_idx];
> + if (mon_idx == -1) {
> + if (mpam_resctrl_abmc_enabled()) {
> + /* Report Unassigned */
> + return -ENOENT;
> + }
> + /* Report Unavailable */
> + return -EINVAL;
> + }
> + }
> +
> + cfg.mon = mon_idx;
> + cfg.match_pmg = true;
> + cfg.partid = closid;
> + cfg.pmg = rmid;
Maybe use
cfg = (struct mon_cfg) {
.mon = ...

and drop the earlier initialization.

};
> +
> + if (irqs_disabled()) {
> + /* Check if we can access this domain without an IPI */
> + return -EIO;
> + }
> +
> + return mpam_msmon_read(mon_comp, &cfg, mon_type, val);
> +}
> +
> +static int read_mon_cdp_safe(struct mpam_resctrl_mon *mon, struct mpam_component *mon_comp,
> + enum mpam_device_features mon_type,
> + int mon_idx, u32 closid, u32 rmid, u64 *val)
> +{
> + if (cdp_enabled) {
> + u64 code_val = 0, data_val = 0;
> + int err;
> +
> + err = __read_mon(mon, mon_comp, mon_type, mon_idx,
> + CDP_CODE, closid, rmid, &code_val);
> + if (err)
> + return err;
> +
> + err = __read_mon(mon, mon_comp, mon_type, mon_idx,
> + CDP_DATA, closid, rmid, &data_val);
> + if (!err)
> + *val += code_val + data_val;

I'd stick to out of line error handling and just spend a couple more lines
for readability.
if (err)
return err;

*val += ..
return 0;

> + return err;
> + }
> +
> + return __read_mon(mon, mon_comp, mon_type, mon_idx,
> + CDP_NONE, closid, rmid, val);
> +}