drm/panfrost: Introduce huge tmpfs mountpoint option

Introduce the 'panfrost.transparent_hugepage' boolean module parameter
(false by default). When the parameter is set to true, a new tmpfs
mountpoint is created and mounted using the 'huge=within_size'
option. It's then used at GEM object creation instead of the default
'shm_mnt' mountpoint in order to enable Transparent Hugepage (THP) for
the object (without having to rely on a system wide parameter).

v3:
- use huge tmpfs mountpoint in drm_device

v4:
- fix builds with CONFIG_TRANSPARENT_HUGEPAGE=n
- clean up mountpoint creation error handling
- print negative error value

v5:
- use drm_gem_has_huge_tmp() helper
- get rid of CONFIG_TRANSPARENT_HUGEPAGE ifdefs

v9:
- replace drm_gem_has_huge_tmp() by drm_gem_get_huge_tmp()

v11:
- enable 'panfrost.transparent_hugepage' by default

Signed-off-by: Loïc Molinari <loic.molinari@collabora.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Link: https://patch.msgid.link/20251205182231.194072-10-loic.molinari@collabora.com
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>

drivers/gpu/drm/panfrost/panfrost_device.c

@@ -12,6 +12,7 @@
 #include "panfrost_device.h"
 #include "panfrost_devfreq.h"
 #include "panfrost_features.h"
+#include "panfrost_gem.h"
 #include "panfrost_issues.h"
 #include "panfrost_gpu.h"
 #include "panfrost_job.h"
@@ -267,6 +268,8 @@ int panfrost_device_init(struct panfrost_device *pfdev)
 	if (err)
 		goto out_job;
 
+	panfrost_gem_init(pfdev);
+
 	return 0;
 out_job:
 	panfrost_jm_fini(pfdev);

drivers/gpu/drm/panfrost/panfrost_drv.c

@@ -858,6 +858,12 @@ static const struct drm_driver panfrost_drm_driver = {
 #endif
 };
 
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+bool panfrost_transparent_hugepage = true;
+module_param_named(transparent_hugepage, panfrost_transparent_hugepage, bool, 0400);
+MODULE_PARM_DESC(transparent_hugepage, "Use a dedicated tmpfs mount point with Transparent Hugepage enabled (true = default)");
+#endif
+
 static int panfrost_probe(struct platform_device *pdev)
 {
 	struct panfrost_device *pfdev;

drivers/gpu/drm/panfrost/panfrost_drv.h

@@ -0,0 +1,9 @@
+/* SPDX-License-Identifier: GPL-2.0 or MIT */
+/* Copyright 2025 Amazon.com, Inc. or its affiliates */
+
+#ifndef __PANFROST_DRV_H__
+#define __PANFROST_DRV_H__
+
+extern bool panfrost_transparent_hugepage;
+
+#endif

drivers/gpu/drm/panfrost/panfrost_gem.c

@@ -1,5 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0
 /* Copyright 2019 Linaro, Ltd, Rob Herring <robh@kernel.org> */
+/* Copyright 2025 Amazon.com, Inc. or its affiliates */
 
 #include <linux/cleanup.h>
 #include <linux/err.h>
@@ -10,9 +11,26 @@
 #include <drm/panfrost_drm.h>
 #include <drm/drm_print.h>
 #include "panfrost_device.h"
+#include "panfrost_drv.h"
 #include "panfrost_gem.h"
 #include "panfrost_mmu.h"
 
+void panfrost_gem_init(struct panfrost_device *pfdev)
+{
+	int err;
+
+	if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) &&
+	    !panfrost_transparent_hugepage)
+		return;
+
+	err = drm_gem_huge_mnt_create(&pfdev->base, "within_size");
+	if (drm_gem_get_huge_mnt(&pfdev->base))
+		drm_info(&pfdev->base, "Using Transparent Hugepage\n");
+	else if (err)
+		drm_warn(&pfdev->base, "Can't use Transparent Hugepage (%d)\n",
+			 err);
+}
+
 #ifdef CONFIG_DEBUG_FS
 static void panfrost_gem_debugfs_bo_add(struct panfrost_device *pfdev,
 					struct panfrost_gem_object *bo)

drivers/gpu/drm/panfrost/panfrost_gem.h

@@ -124,6 +124,8 @@ drm_mm_node_to_panfrost_mapping(struct drm_mm_node *node)
 	return container_of(node, struct panfrost_gem_mapping, mmnode);
 }
 
+void panfrost_gem_init(struct panfrost_device *pfdev);
+
 struct drm_gem_object *panfrost_gem_create_object(struct drm_device *dev, size_t size);
 
 struct drm_gem_object *