drm/panthor: Introduce huge tmpfs mountpoint option

Introduce the 'panthor.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 'panthor.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/20251205182231.194072-9-loic.molinari@collabora.com
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>

drivers/gpu/drm/panthor/panthor_device.c

@@ -18,6 +18,7 @@
 #include "panthor_devfreq.h"
 #include "panthor_device.h"
 #include "panthor_fw.h"
+#include "panthor_gem.h"
 #include "panthor_gpu.h"
 #include "panthor_hw.h"
 #include "panthor_mmu.h"
@@ -294,6 +295,8 @@ int panthor_device_init(struct panthor_device *ptdev)
 	if (ret)
 		goto err_unplug_fw;
 
+	panthor_gem_init(ptdev);
+
 	/* ~3 frames */
 	pm_runtime_set_autosuspend_delay(ptdev->base.dev, 50);
 	pm_runtime_use_autosuspend(ptdev->base.dev);

drivers/gpu/drm/panthor/panthor_drv.c

@@ -1559,6 +1559,7 @@ static const struct file_operations panthor_drm_driver_fops = {
 	.read = drm_read,
 	.llseek = noop_llseek,
 	.mmap = panthor_mmap,
+	.get_unmapped_area = drm_gem_get_unmapped_area,
 	.show_fdinfo = drm_show_fdinfo,
 	.fop_flags = FOP_UNSIGNED_OFFSET,
 };
@@ -1627,6 +1628,12 @@ static const struct drm_driver panthor_drm_driver = {
 #endif
 };
 
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+bool panthor_transparent_hugepage = true;
+module_param_named(transparent_hugepage, panthor_transparent_hugepage, bool, 0400);
+MODULE_PARM_DESC(transparent_hugepage, "Use a dedicated tmpfs mount point with Transparent Hugepage enabled (true = default)");
+#endif
+
 static int panthor_probe(struct platform_device *pdev)
 {
 	struct panthor_device *ptdev;

drivers/gpu/drm/panthor/panthor_drv.h

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

drivers/gpu/drm/panthor/panthor_gem.c

@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0 or MIT
 /* Copyright 2019 Linaro, Ltd, Rob Herring <robh@kernel.org> */
 /* Copyright 2023 Collabora ltd. */
+/* Copyright 2025 Amazon.com, Inc. or its affiliates */
 
 #include <linux/cleanup.h>
 #include <linux/dma-buf.h>
@@ -12,10 +13,27 @@
 #include <drm/panthor_drm.h>
 
 #include "panthor_device.h"
+#include "panthor_drv.h"
 #include "panthor_fw.h"
 #include "panthor_gem.h"
 #include "panthor_mmu.h"
 
+void panthor_gem_init(struct panthor_device *ptdev)
+{
+	int err;
+
+	if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) &&
+	    !panthor_transparent_hugepage)
+		return;
+
+	err = drm_gem_huge_mnt_create(&ptdev->base, "within_size");
+	if (drm_gem_get_huge_mnt(&ptdev->base))
+		drm_info(&ptdev->base, "Using Transparent Hugepage\n");
+	else if (err)
+		drm_warn(&ptdev->base, "Can't use Transparent Hugepage (%d)\n",
+			 err);
+}
+
 #ifdef CONFIG_DEBUG_FS
 static void panthor_gem_debugfs_bo_init(struct panthor_gem_object *bo)
 {

drivers/gpu/drm/panthor/panthor_gem.h

@@ -136,6 +136,8 @@ struct panthor_gem_object *to_panthor_bo(struct drm_gem_object *obj)
 	return container_of(to_drm_gem_shmem_obj(obj), struct panthor_gem_object, base);
 }
 
+void panthor_gem_init(struct panthor_device *ptdev);
+
 struct drm_gem_object *panthor_gem_create_object(struct drm_device *ddev, size_t size);
 
 int