From 44a983d249d05d932b6cff333f130baf70febc22 Mon Sep 17 00:00:00 2001
From: Ali Mashtizadeh <mashti@uwaterloo.ca>
Date: Sun, 1 Mar 2026 22:08:30 +0000
Subject: libpmc: Query hwpmc for caps

This change allows for fine-grained capabilities per counter index. This
is particularly useful for AMD where subclasses are not exposed to the
general PMC code, but other architectures also have asymmetric behaviors
when it comes to specific counter indices.

A new PMC_OP_GETCAPS op is added to the hwpmc(4) ioctl interface.

Reviewed by:	mhorne
Sponsored by:	Netflix
Pull Request:	https://github.com/freebsd/freebsd-src/pull/2058
---
 sys/dev/hwpmc/hwpmc_amd.c | 15 +++++++++++++++
 sys/dev/hwpmc/hwpmc_mod.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 60 insertions(+)

(limited to 'sys/dev')

diff --git a/sys/dev/hwpmc/hwpmc_amd.c b/sys/dev/hwpmc/hwpmc_amd.c
index c27d93995d59..51505bfcff37 100644
--- a/sys/dev/hwpmc/hwpmc_amd.c
+++ b/sys/dev/hwpmc/hwpmc_amd.c
@@ -702,6 +702,20 @@ amd_get_msr(int ri, uint32_t *msr)
 	return (0);
 }
 
+/*
+ * Return the capabilities of the given PMC.
+ */
+static int
+amd_get_caps(int ri, uint32_t *caps)
+{
+	KASSERT(ri >= 0 && ri < amd_npmcs,
+	    ("[amd,%d] ri %d out of range", __LINE__, ri));
+
+	*caps = amd_pmcdesc[ri].pm_descr.pd_caps;
+
+	return (0);
+}
+
 /*
  * Processor-dependent initialization.
  */
@@ -958,6 +972,7 @@ pmc_amd_initialize(void)
 	pcd->pcd_start_pmc	= amd_start_pmc;
 	pcd->pcd_stop_pmc	= amd_stop_pmc;
 	pcd->pcd_write_pmc	= amd_write_pmc;
+	pcd->pcd_get_caps	= amd_get_caps;
 
 	pmc_mdep->pmd_cputype	= cputype;
 	pmc_mdep->pmd_intr	= amd_intr;
diff --git a/sys/dev/hwpmc/hwpmc_mod.c b/sys/dev/hwpmc/hwpmc_mod.c
index 1fa021429c5a..fb1fdf832398 100644
--- a/sys/dev/hwpmc/hwpmc_mod.c
+++ b/sys/dev/hwpmc/hwpmc_mod.c
@@ -4538,6 +4538,51 @@ pmc_syscall_handler(struct thread *td, void *syscall_args)
 	}
 	break;
 
+	/*
+	 * Get the PMC capabilities
+	 */
+
+	case PMC_OP_GETCAPS:
+	{
+		struct pmc_op_caps c;
+		struct pmc *pm;
+		struct pmc_classdep *pcd;
+		pmc_id_t pmcid;
+		int adjri, ri;
+
+		PMC_DOWNGRADE_SX();
+
+		if ((error = copyin(arg, &c, sizeof(c))) != 0)
+			break;
+
+		pmcid = c.pm_pmcid;
+
+		if ((error = pmc_find_pmc(pmcid, &pm)) != 0)
+			break;
+
+		KASSERT(pmcid == pm->pm_id,
+		    ("[pmc,%d] pmc id %x != pmcid %x", __LINE__,
+			pm->pm_id, pmcid));
+
+		ri = PMC_TO_ROWINDEX(pm);
+		pcd = pmc_ri_to_classdep(md, ri, &adjri);
+
+		/*
+		 * If PMC class has no GETCAPS return the class capabilities
+		 * otherwise get the per counter capabilities.
+		 */
+		if (pcd->pcd_get_caps == NULL) {
+			c.pm_caps = pcd->pcd_caps;
+		} else {
+			error = (*pcd->pcd_get_caps)(adjri, &c.pm_caps);
+			if (error < 0)
+				break;
+		}
+
+		if ((error = copyout(&c, arg, sizeof(c))) < 0)
+			break;
+	}
+	break;
 
 	default:
 		error = EINVAL;
-- 
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