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

Jonathan Cameron
2025-09-12T13:21:09Z

On Wed, 10 Sep 2025 20:43:03 +0000
James Morse <james.morse@arm.com> 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>
Hi James,

A couple of minor comments inline,

Jonathan

> +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;

Given nothing to do later, I'd just return at end of each case.
Entirely up to you though as this is just a personal style preference.

> + default:
> + return;
> + }
> +}

> +
> +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);

guard(srcu)(&mpam_srcu);

Then you can do direct returns on errors which looks like it will simplify
things somewhat by letting you just return on err.

> + list_for_each_entry_rcu(vmsc, &comp->vmsc, comp_list) {
> + msc = vmsc->msc;
I'd bring the declaration down here as well.
struct mpam_msc *msc = vmsc->msc;
Could bring ris down here as well.

> +
> + list_for_each_entry_rcu(ris, &vmsc->ris, vmsc_list) {
> + arg->ris = ris;
> +
> + err = smp_call_function_any(&msc->accessibility,
> + __ris_msmon_read, arg,
> + true);
> + if (!err && arg->err)
> + err = arg->err;
> + if (err)
> + break;
> + }
> + if (err)
> + break;

This won't be needed if you returned on error above.

> + }
> + srcu_read_unlock(&mpam_srcu, idx);
> +
> + return err;
And you only reach here with above changes if err == 0 so return 0; appropriate.
> +}
> +
> +int mpam_msmon_read(struct mpam_component *comp, struct mon_cfg *ctx,
> + enum mpam_device_features type, u64 *val)
> +{
> + int err;
> + struct mon_read arg;
> + u64 wait_jiffies = 0;
> + struct mpam_props *cprops = &comp->class->props;
> +
> + might_sleep();
> +
> + if (!mpam_is_enabled())
> + return -EIO;
> +
> + if (!mpam_has_feature(type, cprops))
> + return -EOPNOTSUPP;
> +
> + memset(&arg, 0, sizeof(arg));
Either use = { }; at declaration or maybe
arg = (struct mon_read) {
.ctx = ctx,
.type = type,
.val = val,
};

rather than bothering with separate memset.

> + arg.ctx = ctx;
> + arg.type = type;
> + arg.val = val;
> + *val = 0;
> +
> + err = _msmon_read(comp, &arg);
> + if (err == -EBUSY && comp->class->nrdy_usec)
> + wait_jiffies = usecs_to_jiffies(comp->class->nrdy_usec);
> +
> + while (wait_jiffies)
> + wait_jiffies = schedule_timeout_uninterruptible(wait_jiffies);
> +
> + if (err == -EBUSY) {
> + memset(&arg, 0, sizeof(arg));
Same as above.
> + arg.ctx = ctx;
> + arg.type = type;
> + arg.val = val;
> + *val = 0;
> +
> + err = _msmon_read(comp, &arg);
> + }
> +
> + return err;
> +}