drm/v3d: Introduce gemfs

Commit eb8d395 upstream

Create a separate "tmpfs" kernel mount for V3D. This will allow us to
move away from the shmemfs `shm_mnt` and gives the flexibility to do
things like set our own mount options. Here, the interest is to use
"huge=", which should allow us to enable the use of THP for our
shmem-backed objects.

Signed-off-by: Maíra Canal <mcanal@igalia.com>
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240923141348.2422499-6-mcanal@igalia.com

Author: mairacanal

drivers/gpu/drm/v3d/Makefile

@@ -13,7 +13,8 @@ v3d-y := \
 	v3d_trace_points.o \
 	v3d_sched.o \
 	v3d_sysfs.o \
-	v3d_submit.o
+	v3d_submit.o \
+	v3d_gemfs.o
 
 v3d-$(CONFIG_DEBUG_FS) += v3d_debugfs.o
 

drivers/gpu/drm/v3d/v3d_drv.h

@@ -143,6 +143,11 @@ struct v3d_dev {
 	struct drm_mm mm;
 	spinlock_t mm_lock;
 
+	/*
+	 * tmpfs instance used for shmem backed objects
+	 */
+	struct vfsmount *gemfs;
+
 	struct work_struct overflow_mem_work;
 
 	struct v3d_bin_job *bin_job;
@@ -540,6 +545,10 @@ void v3d_reset(struct v3d_dev *v3d);
 void v3d_invalidate_caches(struct v3d_dev *v3d);
 void v3d_clean_caches(struct v3d_dev *v3d);
 
+/* v3d_gemfs.c */
+void v3d_gemfs_init(struct v3d_dev *v3d);
+void v3d_gemfs_fini(struct v3d_dev *v3d);
+
 /* v3d_submit.c */
 void v3d_job_cleanup(struct v3d_job *job);
 void v3d_job_put(struct v3d_job *job);

drivers/gpu/drm/v3d/v3d_gem.c

@@ -291,6 +291,8 @@ v3d_gem_init(struct drm_device *dev)
 	v3d_init_hw_state(v3d);
 	v3d_mmu_set_page_table(v3d);
 
+	v3d_gemfs_init(v3d);
+
 	ret = v3d_sched_init(v3d);
 	if (ret) {
 		drm_mm_takedown(&v3d->mm);
@@ -308,6 +310,7 @@ v3d_gem_destroy(struct drm_device *dev)
 	struct v3d_dev *v3d = to_v3d_dev(dev);
 
 	v3d_sched_fini(v3d);
+	v3d_gemfs_fini(v3d);
 
 	/* Waiting for jobs to finish would need to be done before
 	 * unregistering V3D.

drivers/gpu/drm/v3d/v3d_gemfs.c

@@ -0,0 +1,46 @@
+// SPDX-License-Identifier: GPL-2.0+
+/* Copyright (C) 2024 Raspberry Pi */
+
+#include <linux/fs.h>
+#include <linux/mount.h>
+
+#include "v3d_drv.h"
+
+void v3d_gemfs_init(struct v3d_dev *v3d)
+{
+	char huge_opt[] = "huge=within_size";
+	struct file_system_type *type;
+	struct vfsmount *gemfs;
+
+	/*
+	 * By creating our own shmemfs mountpoint, we can pass in
+	 * mount flags that better match our usecase. However, we
+	 * only do so on platforms which benefit from it.
+	 */
+	if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE))
+		goto err;
+
+	type = get_fs_type("tmpfs");
+	if (!type)
+		goto err;
+
+	gemfs = vfs_kern_mount(type, SB_KERNMOUNT, type->name, huge_opt);
+	if (IS_ERR(gemfs))
+		goto err;
+
+	v3d->gemfs = gemfs;
+	drm_info(&v3d->drm, "Using Transparent Hugepages\n");
+
+	return;
+
+err:
+	v3d->gemfs = NULL;
+	drm_notice(&v3d->drm,
+		   "Transparent Hugepage support is recommended for optimal performance on this platform!\n");
+}
+
+void v3d_gemfs_fini(struct v3d_dev *v3d)
+{
+	if (v3d->gemfs)
+		kern_unmount(v3d->gemfs);
+}