[RFC 17/23] cgroup: Add the DRM cgroup controller

[Tvrtko Ursulin]

From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>

Skeleton controller without any functionality.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at igalia.com>
---
 include/linux/cgroup_drm.h    |  7 +++++
 include/linux/cgroup_subsys.h |  4 +++
 init/Kconfig                  |  5 +++
 kernel/cgroup/Makefile        |  1 +
 kernel/cgroup/drm.c           | 58 +++++++++++++++++++++++++++++++++++
 5 files changed, 75 insertions(+)
 create mode 100644 include/linux/cgroup_drm.h
 create mode 100644 kernel/cgroup/drm.c

diff --git a/include/linux/cgroup_drm.h b/include/linux/cgroup_drm.h
new file mode 100644
index 000000000000..3e51fe517791
--- /dev/null
+++ b/include/linux/cgroup_drm.h
@@ -0,0 +1,7 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* Copyright (c) 2025 Valve Corporation */
+
+#ifndef _CGROUP_DRM_H
+#define _CGROUP_DRM_H
+
+#endif	/* _CGROUP_DRM_H */
diff --git a/include/linux/cgroup_subsys.h b/include/linux/cgroup_subsys.h
index 3fd0bcbf3080..2ad172c9fba2 100644
--- a/include/linux/cgroup_subsys.h
+++ b/include/linux/cgroup_subsys.h
@@ -69,6 +69,10 @@ SUBSYS(misc)
 SUBSYS(dmem)
 #endif
 
+#if IS_ENABLED(CONFIG_CGROUP_DRM)
+SUBSYS(drm)
+#endif
+
 /*
  * The following subsystems are not supported on the default hierarchy.
  */
diff --git a/init/Kconfig b/init/Kconfig
index 63f5974b9fa6..02789e15c6e6 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1157,6 +1157,11 @@ config CGROUP_DMEM
 	  As an example, it allows you to restrict VRAM usage for applications
 	  in the DRM subsystem.
 
+config CGROUP_DRM
+	bool "DRM controller"
+	help
+	  Provides the DRM subsystem controller.
+
 config CGROUP_FREEZER
 	bool "Freezer controller"
 	help
diff --git a/kernel/cgroup/Makefile b/kernel/cgroup/Makefile
index ede31601a363..c39799312cfd 100644
--- a/kernel/cgroup/Makefile
+++ b/kernel/cgroup/Makefile
@@ -8,4 +8,5 @@ obj-$(CONFIG_CPUSETS) += cpuset.o
 obj-$(CONFIG_CPUSETS_V1) += cpuset-v1.o
 obj-$(CONFIG_CGROUP_MISC) += misc.o
 obj-$(CONFIG_CGROUP_DMEM) += dmem.o
+obj-$(CONFIG_CGROUP_DRM) += drm.o
 obj-$(CONFIG_CGROUP_DEBUG) += debug.o
diff --git a/kernel/cgroup/drm.c b/kernel/cgroup/drm.c
new file mode 100644
index 000000000000..55947a009e04
--- /dev/null
+++ b/kernel/cgroup/drm.c
@@ -0,0 +1,58 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2025 Valve Corporation */
+
+#include <linux/cgroup.h>
+#include <linux/cgroup_drm.h>
+#include <linux/slab.h>
+
+struct drm_cgroup_state {
+	struct cgroup_subsys_state css;
+};
+
+struct drm_root_cgroup_state {
+	struct drm_cgroup_state drmcs;
+};
+
+static struct drm_root_cgroup_state root_drmcs;
+
+static inline struct drm_cgroup_state *
+css_to_drmcs(struct cgroup_subsys_state *css)
+{
+	return container_of(css, struct drm_cgroup_state, css);
+}
+
+static void drmcs_free(struct cgroup_subsys_state *css)
+{
+	struct drm_cgroup_state *drmcs = css_to_drmcs(css);
+
+	if (drmcs != &root_drmcs.drmcs)
+		kfree(drmcs);
+}
+
+static struct cgroup_subsys_state *
+drmcs_alloc(struct cgroup_subsys_state *parent_css)
+{
+	struct drm_cgroup_state *drmcs;
+
+	if (!parent_css) {
+		drmcs = &root_drmcs.drmcs;
+	} else {
+		drmcs = kzalloc(sizeof(*drmcs), GFP_KERNEL);
+		if (!drmcs)
+			return ERR_PTR(-ENOMEM);
+	}
+
+	return &drmcs->css;
+}
+
+struct cftype files[] = {
+	{ } /* Zero entry terminates. */
+};
+
+struct cgroup_subsys drm_cgrp_subsys = {
+	.css_alloc	= drmcs_alloc,
+	.css_free	= drmcs_free,
+	.early_init	= false,
+	.legacy_cftypes	= files,
+	.dfl_cftypes	= files,
+};
-- 
2.48.0