[PATCH v9 11/12] x86/resctrl: Introduce erdt_cpu_has() and erdt_support()

[Chen Yu]

Introduce erdt_cpu_has() to verify if a specific RDT feature is backed by an
ERDT table. A feature is only reported as ERDT backed when the CPU enumerates
it via CPUID and firmware describes it in the ERDT table (and its sub-tables).
erdt_cpu_has() also considers userspace input like "rdt=!cmt". Similar to
rdt_cpu_has(), erdt_cpu_has() expects an x86 feature flag as parameter.

Introduce erdt_support() as a helper called by erdt_cpu_has() to check whether
the ERDT firmware supports a given feature.

erdt_support() deliberately claims no feature yet and returns false. Features
should be added to erdt_support() as their MMIO implementations are introduced.

Suggested-by: Reinette Chatre <reinette.chatre@xxxxxxxxx>
Signed-off-by: Chen Yu <yu.c.chen@xxxxxxxxx>
Tested-by: Hongyu Ning <hongyu.ning@xxxxxxxxxxxxxxx>
---
Changes since v8:
- Factor the "rdt=" option handling out of rdt_cpu_has() into
  apply_rdt_options() and build both rdt_cpu_has() and erdt_cpu_has() on
  top of it instead of duplicating the loop. (Reinette Chatre)
- CPUID stays the architectural enumeration mechanism, so erdt_cpu_has()
  now requires boot_cpu_has(flag) in addition to ERDT firmware support.
  (Reinette Chatre)
- Do not add the erdt_cpu_has()/erdt_get_scale() prototypes to
  asm/resctrl.h, they live in the resctrl internal header now that
  resctrl_arch_round_mon_val() is out of line. (Reinette Chatre)
- Reword the changelog: use imperative mood instead of "is derived
  from", and do not imply that rdt_cpu_has() considers ERDT.
  (Reinette Chatre)

 arch/x86/kernel/cpu/resctrl/core.c     | 13 +++++++++++--
 arch/x86/kernel/cpu/resctrl/erdt.c     |  5 +++++
 arch/x86/kernel/cpu/resctrl/internal.h |  2 ++
 3 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
index 9a59643f366c..f8737d9b2e20 100644
--- a/arch/x86/kernel/cpu/resctrl/core.c
+++ b/arch/x86/kernel/cpu/resctrl/core.c
@@ -872,9 +872,8 @@ static int __init set_rdt_options(char *str)
 }
 __setup("rdt", set_rdt_options);
 
-bool rdt_cpu_has(int flag)
+static bool apply_rdt_options(int flag, bool ret)
 {
-	bool ret = boot_cpu_has(flag);
 	struct rdt_options *o;
 
 	if (!ret)
@@ -892,6 +891,16 @@ bool rdt_cpu_has(int flag)
 	return ret;
 }
 
+bool rdt_cpu_has(int flag)
+{
+	return apply_rdt_options(flag, boot_cpu_has(flag));
+}
+
+bool erdt_cpu_has(int flag)
+{
+	return apply_rdt_options(flag, boot_cpu_has(flag) && erdt_support(flag));
+}
+
 bool resctrl_arch_is_evt_configurable(enum resctrl_event_id evt)
 {
 	if (!rdt_cpu_has(X86_FEATURE_BMEC))
diff --git a/arch/x86/kernel/cpu/resctrl/erdt.c b/arch/x86/kernel/cpu/resctrl/erdt.c
index 1e6cfc6dbc38..110e7b9806b4 100644
--- a/arch/x86/kernel/cpu/resctrl/erdt.c
+++ b/arch/x86/kernel/cpu/resctrl/erdt.c
@@ -50,6 +50,11 @@ static unsigned int erdt_max_rmid;
  */
 static unsigned int erdt_scale;
 
+bool erdt_support(int flag)
+{
+	return false;
+}
+
 unsigned int erdt_get_scale(void)
 {
 	return erdt_scale;
diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
index 0de174df26e9..88fae7a84fc7 100644
--- a/arch/x86/kernel/cpu/resctrl/internal.h
+++ b/arch/x86/kernel/cpu/resctrl/internal.h
@@ -288,6 +288,8 @@ static inline void intel_aet_mon_domain_setup(int cpu, int id, struct rdt_resour
 static inline bool intel_handle_aet_option(bool force_off, char *tok) { return false; }
 #endif
 
+bool erdt_cpu_has(int flag);
+bool erdt_support(int flag);
 unsigned int erdt_get_scale(void);
 void erdt_init(void);
 void erdt_exit(void);
-- 
2.43.0