[RFC PATCH 4/5] drm/panthor: Add support for protected memory allocation in panthor

Florent Tomasin
2025-01-30T13:12:34Z

This patch allows Panthor to allocate buffer objects from a
protected heap. The Panthor driver should be seen as a consumer
of the heap and not an exporter.

To help with the review of this patch, here are important information
about the Mali GPU protected mode support:
- On CSF FW load, the Panthor driver must allocate a protected
buffer object to hold data to use by the FW when in protected
mode. This protected buffer object is owned by the device
and does not belong to a process.
- On CSG creation, the Panthor driver must allocate a protected
suspend buffer object for the FW to store data when suspending
the CSG while in protected mode. The kernel owns this allocation
and does not allow user space mapping. The format of the data
in this buffer is only known by the FW and does not need to be
shared with other entities.

To summarize, Mali GPUs require allocations of protected buffer
objects at the kernel level.

* How is the protected heap accessed by the Panthor driver?
The driver will retrieve the protected heap using the name of the
heap provided to the driver via the DTB as attribute.
If the heap is not yet available, the panthor driver will defer
the probe until created. It is an integration error to provide
a heap name that does not exist or is never created in the
DTB node.

* How is the Panthor driver allocating from the heap?
Panthor is calling the DMA heap allocation function
and obtains a DMA buffer from it. This buffer is then
registered to GEM via PRIME by importing the DMA buffer.

Signed-off-by: Florent Tomasin <florent.tomasin@arm.com>
---
drivers/gpu/drm/panthor/Kconfig | 1 +
drivers/gpu/drm/panthor/panthor_device.c | 22 ++++++++++-
drivers/gpu/drm/panthor/panthor_device.h | 7 ++++
drivers/gpu/drm/panthor/panthor_fw.c | 36 +++++++++++++++--
drivers/gpu/drm/panthor/panthor_fw.h | 2 +
drivers/gpu/drm/panthor/panthor_gem.c | 49 ++++++++++++++++++++++--
drivers/gpu/drm/panthor/panthor_gem.h | 16 +++++++-
drivers/gpu/drm/panthor/panthor_heap.c | 2 +
drivers/gpu/drm/panthor/panthor_sched.c | 5 ++-
9 files changed, 130 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/panthor/Kconfig b/drivers/gpu/drm/panthor/Kconfig
index 55b40ad07f3b..c0208b886d9f 100644
--- a/drivers/gpu/drm/panthor/Kconfig
+++ b/drivers/gpu/drm/panthor/Kconfig
@@ -7,6 +7,7 @@ config DRM_PANTHOR
depends on !GENERIC_ATOMIC64 # for IOMMU_IO_PGTABLE_LPAE
depends on MMU
select DEVFREQ_GOV_SIMPLE_ONDEMAND
+ select DMABUF_HEAPS
select DRM_EXEC
select DRM_GEM_SHMEM_HELPER
select DRM_GPUVM
diff --git a/drivers/gpu/drm/panthor/panthor_device.c b/drivers/gpu/drm/panthor/panthor_device.c
index 00f7b8ce935a..1018e5c90a0e 100644
--- a/drivers/gpu/drm/panthor/panthor_device.c
+++ b/drivers/gpu/drm/panthor/panthor_device.c
@@ -4,7 +4,9 @@
/* Copyright 2023 Collabora ltd. */

#include <linux/clk.h>
+#include <linux/dma-heap.h>
#include <linux/mm.h>
+#include <linux/of.h>
#include <linux/platform_device.h>
#include <linux/pm_domain.h>
#include <linux/pm_runtime.h>
@@ -102,6 +104,9 @@ void panthor_device_unplug(struct panthor_device *ptdev)
panthor_mmu_unplug(ptdev);
panthor_gpu_unplug(ptdev);

+ if (ptdev->protm.heap)
+ dma_heap_put(ptdev->protm.heap);
+
pm_runtime_dont_use_autosuspend(ptdev->base.dev);
pm_runtime_put_sync_suspend(ptdev->base.dev);

@@ -172,6 +177,7 @@ int panthor_device_init(struct panthor_device *ptdev)
u32 *dummy_page_virt;
struct resource *res;
struct page *p;
+ const char *protm_heap_name;
int ret;

ret = panthor_gpu_coherency_init(ptdev);
@@ -246,9 +252,19 @@ int panthor_device_init(struct panthor_device *ptdev)
return ret;
}

+ /* If a protected heap is specified but not found, defer the probe until created */
+ if (!of_property_read_string(ptdev->base.dev->of_node, "protected-heap-name",
+ &protm_heap_name)) {
+ ptdev->protm.heap = dma_heap_find(protm_heap_name);
+ if (!ptdev->protm.heap) {
+ ret = -EPROBE_DEFER;
+ goto err_rpm_put;
+ }
+ }
+
ret = panthor_gpu_init(ptdev);
if (ret)
- goto err_rpm_put;
+ goto err_dma_heap_put;

ret = panthor_mmu_init(ptdev);
if (ret)
@@ -286,6 +302,10 @@ int panthor_device_init(struct panthor_device *ptdev)
err_unplug_gpu:
panthor_gpu_unplug(ptdev);

+err_dma_heap_put:
+ if (ptdev->protm.heap)
+ dma_heap_put(ptdev->protm.heap);
+
err_rpm_put:
pm_runtime_put_sync_suspend(ptdev->base.dev);
return ret;
diff --git a/drivers/gpu/drm/panthor/panthor_device.h b/drivers/gpu/drm/panthor/panthor_device.h
index 0e68f5a70d20..406de9e888e2 100644
--- a/drivers/gpu/drm/panthor/panthor_device.h
+++ b/drivers/gpu/drm/panthor/panthor_device.h
@@ -7,6 +7,7 @@
#define __PANTHOR_DEVICE_H__

#include <linux/atomic.h>
+#include <linux/dma-heap.h>
#include <linux/io-pgtable.h>
#include <linux/regulator/consumer.h>
#include <linux/sched.h>
@@ -190,6 +191,12 @@ struct panthor_device {

/** @fast_rate: Maximum device clock frequency. Set by DVFS */
unsigned long fast_rate;
+
+ /** @protm: Protected mode related data. */
+ struct {
+ /** @heap: Pointer to the protected heap */
+ struct dma_heap *heap;
+ } protm;
};

struct panthor_gpu_usage {
diff --git a/drivers/gpu/drm/panthor/panthor_fw.c b/drivers/gpu/drm/panthor/panthor_fw.c
index 4a2e36504fea..7822af1533b4 100644
--- a/drivers/gpu/drm/panthor/panthor_fw.c
+++ b/drivers/gpu/drm/panthor/panthor_fw.c
@@ -458,6 +458,7 @@ panthor_fw_alloc_queue_iface_mem(struct panthor_device *ptdev,

mem = panthor_kernel_bo_create(ptdev, ptdev->fw->vm, SZ_8K,
DRM_PANTHOR_BO_NO_MMAP,
+ 0,
DRM_PANTHOR_VM_BIND_OP_MAP_NOEXEC |
DRM_PANTHOR_VM_BIND_OP_MAP_UNCACHED,
PANTHOR_VM_KERNEL_AUTO_VA);
@@ -491,6 +492,28 @@ panthor_fw_alloc_suspend_buf_mem(struct panthor_device *ptdev, size_t size)
{
return panthor_kernel_bo_create(ptdev, panthor_fw_vm(ptdev), size,
DRM_PANTHOR_BO_NO_MMAP,
+ 0,
+ DRM_PANTHOR_VM_BIND_OP_MAP_NOEXEC,
+ PANTHOR_VM_KERNEL_AUTO_VA);
+}
+
+/**
+ * panthor_fw_alloc_protm_suspend_buf_mem() - Allocate a protm suspend buffer
+ * for a command stream group.
+ * @ptdev: Device.
+ * @size: Size of the protm suspend buffer.
+ *
+ * Return: A valid pointer in case of success, NULL if no protected heap, an ERR_PTR() otherwise.
+ */
+struct panthor_kernel_bo *
+panthor_fw_alloc_protm_suspend_buf_mem(struct panthor_device *ptdev, size_t size)
+{
+ if (!ptdev->protm.heap)
+ return NULL;
+
+ return panthor_kernel_bo_create(ptdev, panthor_fw_vm(ptdev), size,
+ DRM_PANTHOR_BO_NO_MMAP,
+ DRM_PANTHOR_KBO_PROTECTED_HEAP,
DRM_PANTHOR_VM_BIND_OP_MAP_NOEXEC,
PANTHOR_VM_KERNEL_AUTO_VA);
}
@@ -503,6 +526,7 @@ static int panthor_fw_load_section_entry(struct panthor_device *ptdev,
ssize_t vm_pgsz = panthor_vm_page_size(ptdev->fw->vm);
struct panthor_fw_binary_section_entry_hdr hdr;
struct panthor_fw_section *section;
+ bool is_protm_section = false;
u32 section_size;
u32 name_len;
int ret;
@@ -541,10 +565,13 @@ static int panthor_fw_load_section_entry(struct panthor_device *ptdev,
return -EINVAL;
}

- if (hdr.flags & CSF_FW_BINARY_IFACE_ENTRY_PROT) {
+ if ((hdr.flags & CSF_FW_BINARY_IFACE_ENTRY_PROT) && !ptdev->protm.heap) {
drm_warn(&ptdev->base,
"Firmware protected mode entry not be supported, ignoring");
return 0;
+ } else if ((hdr.flags & CSF_FW_BINARY_IFACE_ENTRY_PROT) && ptdev->protm.heap) {
+ drm_info(&ptdev->base, "Firmware protected mode entry supported");
+ is_protm_section = true;
}

if (hdr.va.start == CSF_MCU_SHARED_REGION_START &&
@@ -610,9 +637,10 @@ static int panthor_fw_load_section_entry(struct panthor_device *ptdev,
vm_map_flags |= DRM_PANTHOR_VM_BIND_OP_MAP_UNCACHED;

section->mem = panthor_kernel_bo_create(ptdev, panthor_fw_vm(ptdev),
- section_size,
- DRM_PANTHOR_BO_NO_MMAP,
- vm_map_flags, va);
+ section_size,
+ DRM_PANTHOR_BO_NO_MMAP,
+ (is_protm_section ? DRM_PANTHOR_KBO_PROTECTED_HEAP : 0),
+ vm_map_flags, va);
if (IS_ERR(section->mem))
return PTR_ERR(section->mem);

diff --git a/drivers/gpu/drm/panthor/panthor_fw.h b/drivers/gpu/drm/panthor/panthor_fw.h
index 22448abde992..29042d0dc60c 100644
--- a/drivers/gpu/drm/panthor/panthor_fw.h
+++ b/drivers/gpu/drm/panthor/panthor_fw.h
@@ -481,6 +481,8 @@ panthor_fw_alloc_queue_iface_mem(struct panthor_device *ptdev,
u32 *input_fw_va, u32 *output_fw_va);
struct panthor_kernel_bo *
panthor_fw_alloc_suspend_buf_mem(struct panthor_device *ptdev, size_t size);
+struct panthor_kernel_bo *
+panthor_fw_alloc_protm_suspend_buf_mem(struct panthor_device *ptdev, size_t size);

struct panthor_vm *panthor_fw_vm(struct panthor_device *ptdev);

diff --git a/drivers/gpu/drm/panthor/panthor_gem.c b/drivers/gpu/drm/panthor/panthor_gem.c
index 8244a4e6c2a2..88caf928acd0 100644
--- a/drivers/gpu/drm/panthor/panthor_gem.c
+++ b/drivers/gpu/drm/panthor/panthor_gem.c
@@ -9,10 +9,14 @@

#include <drm/panthor_drm.h>

+#include <uapi/linux/dma-heap.h>
+
#include "panthor_device.h"
#include "panthor_gem.h"
#include "panthor_mmu.h"

+MODULE_IMPORT_NS(DMA_BUF);
+
static void panthor_gem_free_object(struct drm_gem_object *obj)
{
struct panthor_gem_object *bo = to_panthor_bo(obj);
@@ -31,6 +35,7 @@ static void panthor_gem_free_object(struct drm_gem_object *obj)
*/
void panthor_kernel_bo_destroy(struct panthor_kernel_bo *bo)
{
+ struct dma_buf *dma_bo = NULL;
struct panthor_vm *vm;
int ret;

@@ -38,6 +43,10 @@ void panthor_kernel_bo_destroy(struct panthor_kernel_bo *bo)
return;

vm = bo->vm;
+
+ if (bo->flags & DRM_PANTHOR_KBO_PROTECTED_HEAP)
+ dma_bo = bo->obj->import_attach->dmabuf;
+
panthor_kernel_bo_vunmap(bo);

if (drm_WARN_ON(bo->obj->dev,
@@ -51,6 +60,9 @@ void panthor_kernel_bo_destroy(struct panthor_kernel_bo *bo)
panthor_vm_free_va(vm, &bo->va_node);
drm_gem_object_put(bo->obj);

+ if (dma_bo)
+ dma_buf_put(dma_bo);
+
out_free_bo:
panthor_vm_put(vm);
kfree(bo);
@@ -62,6 +74,7 @@ void panthor_kernel_bo_destroy(struct panthor_kernel_bo *bo)
* @vm: VM to map the GEM to. If NULL, the kernel object is not GPU mapped.
* @size: Size of the buffer object.
* @bo_flags: Combination of drm_panthor_bo_flags flags.
+ * @kbo_flags: Combination of drm_panthor_kbo_flags flags.
* @vm_map_flags: Combination of drm_panthor_vm_bind_op_flags (only those
* that are related to map operations).
* @gpu_va: GPU address assigned when mapping to the VM.
@@ -72,9 +85,11 @@ void panthor_kernel_bo_destroy(struct panthor_kernel_bo *bo)
*/
struct panthor_kernel_bo *
panthor_kernel_bo_create(struct panthor_device *ptdev, struct panthor_vm *vm,
- size_t size, u32 bo_flags, u32 vm_map_flags,
+ size_t size, u32 bo_flags, u32 kbo_flags, u32 vm_map_flags,
u64 gpu_va)
{
+ struct dma_buf *dma_bo = NULL;
+ struct drm_gem_object *gem_obj = NULL;
struct drm_gem_shmem_object *obj;
struct panthor_kernel_bo *kbo;
struct panthor_gem_object *bo;
@@ -87,14 +102,38 @@ panthor_kernel_bo_create(struct panthor_device *ptdev, struct panthor_vm *vm,
if (!kbo)
return ERR_PTR(-ENOMEM);

- obj = drm_gem_shmem_create(&ptdev->base, size);
+ if (kbo_flags & DRM_PANTHOR_KBO_PROTECTED_HEAP) {
+ if (!ptdev->protm.heap) {
+ ret = -EINVAL;
+ goto err_free_bo;
+ }
+
+ dma_bo = dma_heap_buffer_alloc(ptdev->protm.heap, size,
+ DMA_HEAP_VALID_FD_FLAGS, DMA_HEAP_VALID_HEAP_FLAGS);
+ if (!dma_bo) {
+ ret = -ENOMEM;
+ goto err_free_bo;
+ }
+
+ gem_obj = drm_gem_prime_import(&ptdev->base, dma_bo);
+ if (IS_ERR(gem_obj)) {
+ ret = PTR_ERR(gem_obj);
+ goto err_free_dma_bo;
+ }
+
+ obj = to_drm_gem_shmem_obj(gem_obj);
+ } else {
+ obj = drm_gem_shmem_create(&ptdev->base, size);
+ }
+
if (IS_ERR(obj)) {
ret = PTR_ERR(obj);
- goto err_free_bo;
+ goto err_free_dma_bo;
}

bo = to_panthor_bo(&obj->base);
kbo->obj = &obj->base;
+ kbo->flags = kbo_flags;
bo->flags = bo_flags;

/* The system and GPU MMU page size might differ, which becomes a
@@ -124,6 +163,10 @@ panthor_kernel_bo_create(struct panthor_device *ptdev, struct panthor_vm *vm,
err_put_obj:
drm_gem_object_put(&obj->base);

+err_free_dma_bo:
+ if (dma_bo)
+ dma_buf_put(dma_bo);
+
err_free_bo:
kfree(kbo);
return ERR_PTR(ret);
diff --git a/drivers/gpu/drm/panthor/panthor_gem.h b/drivers/gpu/drm/panthor/panthor_gem.h
index e43021cf6d45..d4fe8ae9f0a8 100644
--- a/drivers/gpu/drm/panthor/panthor_gem.h
+++ b/drivers/gpu/drm/panthor/panthor_gem.h
@@ -13,6 +13,17 @@

struct panthor_vm;

+/**
+ * enum drm_panthor_kbo_flags - Kernel buffer object flags, passed at creation time
+ */
+enum drm_panthor_kbo_flags {
+ /**
+ * @DRM_PANTHOR_KBO_PROTECTED_HEAP: The buffer object will be allocated
+ * from a DMA-Buf protected heap.
+ */
+ DRM_PANTHOR_KBO_PROTECTED_HEAP = (1 << 0),
+};
+
/**
* struct panthor_gem_object - Driver specific GEM object.
*/
@@ -75,6 +86,9 @@ struct panthor_kernel_bo {
* @kmap: Kernel CPU mapping of @gem.
*/
void *kmap;
+
+ /** @flags: Combination of drm_panthor_kbo_flags flags. */
+ u32 flags;
};

static inline
@@ -138,7 +152,7 @@ panthor_kernel_bo_vunmap(struct panthor_kernel_bo *bo)

struct panthor_kernel_bo *
panthor_kernel_bo_create(struct panthor_device *ptdev, struct panthor_vm *vm,
- size_t size, u32 bo_flags, u32 vm_map_flags,
+ size_t size, u32 bo_flags, u32 kbo_flags, u32 vm_map_flags,
u64 gpu_va);

void panthor_kernel_bo_destroy(struct panthor_kernel_bo *bo);
diff --git a/drivers/gpu/drm/panthor/panthor_heap.c b/drivers/gpu/drm/panthor/panthor_heap.c
index 3796a9eb22af..5395f0d90360 100644
--- a/drivers/gpu/drm/panthor/panthor_heap.c
+++ b/drivers/gpu/drm/panthor/panthor_heap.c
@@ -146,6 +146,7 @@ static int panthor_alloc_heap_chunk(struct panthor_device *ptdev,

chunk->bo = panthor_kernel_bo_create(ptdev, vm, heap->chunk_size,
DRM_PANTHOR_BO_NO_MMAP,
+ 0,
DRM_PANTHOR_VM_BIND_OP_MAP_NOEXEC,
PANTHOR_VM_KERNEL_AUTO_VA);
if (IS_ERR(chunk->bo)) {
@@ -549,6 +550,7 @@ panthor_heap_pool_create(struct panthor_device *ptdev, struct panthor_vm *vm)

pool->gpu_contexts = panthor_kernel_bo_create(ptdev, vm, bosize,
DRM_PANTHOR_BO_NO_MMAP,
+ 0,
DRM_PANTHOR_VM_BIND_OP_MAP_NOEXEC,
PANTHOR_VM_KERNEL_AUTO_VA);
if (IS_ERR(pool->gpu_contexts)) {
diff --git a/drivers/gpu/drm/panthor/panthor_sched.c b/drivers/gpu/drm/panthor/panthor_sched.c
index ef4bec7ff9c7..e260ed8aef5b 100644
--- a/drivers/gpu/drm/panthor/panthor_sched.c
+++ b/drivers/gpu/drm/panthor/panthor_sched.c
@@ -3298,6 +3298,7 @@ group_create_queue(struct panthor_group *group,
queue->ringbuf = panthor_kernel_bo_create(group->ptdev, group->vm,
args->ringbuf_size,
DRM_PANTHOR_BO_NO_MMAP,
+ 0,
DRM_PANTHOR_VM_BIND_OP_MAP_NOEXEC |
DRM_PANTHOR_VM_BIND_OP_MAP_UNCACHED,
PANTHOR_VM_KERNEL_AUTO_VA);
@@ -3328,6 +3329,7 @@ group_create_queue(struct panthor_group *group,
queue->profiling.slot_count *
sizeof(struct panthor_job_profiling_data),
DRM_PANTHOR_BO_NO_MMAP,
+ 0,
DRM_PANTHOR_VM_BIND_OP_MAP_NOEXEC |
DRM_PANTHOR_VM_BIND_OP_MAP_UNCACHED,
PANTHOR_VM_KERNEL_AUTO_VA);
@@ -3435,7 +3437,7 @@ int panthor_group_create(struct panthor_file *pfile,
}

suspend_size = csg_iface->control->protm_suspend_size;
- group->protm_suspend_buf = panthor_fw_alloc_suspend_buf_mem(ptdev, suspend_size);
+ group->protm_suspend_buf = panthor_fw_alloc_protm_suspend_buf_mem(ptdev, suspend_size);
if (IS_ERR(group->protm_suspend_buf)) {
ret = PTR_ERR(group->protm_suspend_buf);
group->protm_suspend_buf = NULL;
@@ -3446,6 +3448,7 @@ int panthor_group_create(struct panthor_file *pfile,
group_args->queues.count *
sizeof(struct panthor_syncobj_64b),
DRM_PANTHOR_BO_NO_MMAP,
+ 0,
DRM_PANTHOR_VM_BIND_OP_MAP_NOEXEC |
DRM_PANTHOR_VM_BIND_OP_MAP_UNCACHED,
PANTHOR_VM_KERNEL_AUTO_VA);
--
2.34.1