linux-kernel - Re: [RFC PATCH 25/38] arm_mpam: resctrl: Add resctrl_arch_rmid_read() and resctrl_arch_reset

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Message-ID: <20251218135317.000004ba@huawei.com>
Date: Thu, 18 Dec 2025 13:53:17 +0000
From: Jonathan Cameron <jonathan.cameron@...wei.com>
To: James Morse <james.morse@....com>
CC: <linux-kernel@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>, D
 Scott Phillips OS <scott@...amperecomputing.com>,
	<carl@...amperecomputing.com>, <lcherian@...vell.com>,
	<bobo.shaobowang@...wei.com>, <tan.shaopeng@...itsu.com>,
	<baolin.wang@...ux.alibaba.com>, Jamie Iles <quic_jiles@...cinc.com>, "Xin
 Hao" <xhao@...ux.alibaba.com>, <peternewman@...gle.com>,
	<dfustini@...libre.com>, <amitsinght@...vell.com>, David Hildenbrand
	<david@...nel.org>, Dave Martin <dave.martin@....com>, Koba Ko
	<kobak@...dia.com>, Shanker Donthineni <sdonthineni@...dia.com>,
	<fenghuay@...dia.com>, <baisheng.gao@...soc.com>, Gavin Shan
	<gshan@...hat.com>, Ben Horgan <ben.horgan@....com>, <rohit.mathew@....com>,
	<reinette.chatre@...el.com>, Punit Agrawal <punit.agrawal@....qualcomm.com>
Subject: Re: [RFC PATCH 25/38] arm_mpam: resctrl: Add
 resctrl_arch_rmid_read() and resctrl_arch_reset_rmid()

On Fri, 5 Dec 2025 21:58:48 +0000
James Morse <james.morse@....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@....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);
> +}