linux-kernel - [RFC PATCH 27/38] arm_mpam: resctrl: Add empty definitions for assorted resctrl functions

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Message-Id: <20251205215901.17772-28-james.morse@arm.com>
Date: Fri,  5 Dec 2025 21:58:50 +0000
From: James Morse <james.morse@....com>
To: linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Cc: James Morse <james.morse@....com>,
	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,
	Jonathan Cameron <jonathan.cameron@...wei.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: [RFC PATCH 27/38] arm_mpam: resctrl: Add empty definitions for assorted resctrl functions

A few resctrl features and hooks need to be provided, but aren't needed
or supported on MPAM platforms.

resctrl has individual hooks to separately enable and disable the
closid/partid and rmid/pmg context switching code. For MPAM this is all
the same thing, as the value in struct task_struct is used to cache the
value that should be written to hardware. arm64's context switching code
is enabled once MPAM is usable, but doesn't touch the hardware unless
the value has changed.

For now event configuration is not supported, and can be turned off
by returning 'false' from resctrl_arch_is_evt_configurable().

Add this, and empty definitions for the other hooks.

Signed-off-by: James Morse <james.morse@....com>
---
 drivers/resctrl/mpam_resctrl.c | 17 +++++++++++++++++
 include/linux/arm_mpam.h       |  9 +++++++++
 2 files changed, 26 insertions(+)

diff --git a/drivers/resctrl/mpam_resctrl.c b/drivers/resctrl/mpam_resctrl.c
index 1333dc40714a..00455de3efe9 100644
--- a/drivers/resctrl/mpam_resctrl.c
+++ b/drivers/resctrl/mpam_resctrl.c
@@ -85,6 +85,23 @@ bool resctrl_arch_mon_capable(void)
 	return exposed_mon_capable;
 }
 
+bool resctrl_arch_is_evt_configurable(enum resctrl_event_id evt)
+{
+	return false;
+}
+
+void resctrl_arch_mon_event_config_read(void *info)
+{
+}
+
+void resctrl_arch_mon_event_config_write(void *info)
+{
+}
+
+void resctrl_arch_reset_rmid_all(struct rdt_resource *r, struct rdt_mon_domain *d)
+{
+}
+
 bool resctrl_arch_get_cdp_enabled(enum resctrl_res_level rid)
 {
 	switch (rid) {
diff --git a/include/linux/arm_mpam.h b/include/linux/arm_mpam.h
index 86d5e326d2bd..f92a36187a52 100644
--- a/include/linux/arm_mpam.h
+++ b/include/linux/arm_mpam.h
@@ -67,6 +67,15 @@ struct rdt_resource;
 void *resctrl_arch_mon_ctx_alloc(struct rdt_resource *r, enum resctrl_event_id evtid);
 void resctrl_arch_mon_ctx_free(struct rdt_resource *r, enum resctrl_event_id evtid, void *ctx);
 
+/*
+ * The CPU configuration for MPAM is cheap to write, and is only written if it
+ * has changed. No need for fine grained enables.
+ */
+static inline void resctrl_arch_enable_mon(void) { }
+static inline void resctrl_arch_disable_mon(void) { }
+static inline void resctrl_arch_enable_alloc(void) { }
+static inline void resctrl_arch_disable_alloc(void) { }
+
 static inline unsigned int resctrl_arch_round_mon_val(unsigned int val)
 {
 	return val;
-- 
2.39.5