[PATCH] RFC: drm/lima: fix calling drm_mm_init with an empty range

[Alban Browaeys <alban.browaeys@xxxxxxxxx>]

For the empty_vm initialization the range is empty which is not supported
by drm_mm_init.

With CONFIG_DRM_DEBUG_MM set, I get:
------------[ cut here ]------------
 kernel BUG at drivers/gpu/drm/drm_mm.c:965!
 Internal error: Oops - BUG: 0 [#1] PREEMPT SMP ARM
 Modules linked in: lima(+) drm_shmem_helper gpu_sched s5p_jpeg s5p_g2d
 videobuf2_dma_contig videobuf2_memops v4l2_mem2mem videobuf2_v4l2
 videobuf2_common s5p_cec tun fuse configfs auth_rpcgss sunrpc ip_tables
 x_tables autofs4 btrfs lzo_compress zlib_deflate raid10 raid456
 async_raid6_recov async_memcpy async_pq async_xor async_tx xor xor_neon
 raid6_pq libcrc32c raid1 raid0 linear md_mod dm_mirror dm_region_hash
 dm_log hid_logitech_hidpp hid_logitech_dj
 CPU: 0 PID: 1033 Comm: systemd-udevd Not tainted 6.4.0-rc1-debug+ #230
 Hardware name: Samsung Exynos (Flattened Device Tree)
 PC is at drm_mm_init+0x94/0x98
 LR is at 0x0
 Flags: nZCv  IRQs on  FIQs off  Mode SVC_32  ISA ARM  Segment none
  drm_mm_init from lima_vm_create+0xcc/0x108 [lima]
  lima_vm_create [lima] from lima_device_init+0xd8/0x4a0 [lima]
  lima_device_init [lima] from lima_pdev_probe.part.0+0x6c/0x158 [lima]
  lima_pdev_probe.part.0 [lima] from platform_probe+0x64/0xc0
  platform_probe from call_driver_probe+0x2c/0x110

The drm_mm.c line 965 is:
drivers/gpu/drm/drm_mm.c
void drm_mm_init(struct drm_mm *mm, u64 start, u64 size)
{
        DRM_MM_BUG_ON(start + size <= start);

lima_vm_create is called with va_start and va_end both unset
in lima_device_init line 371:
ldev->empty_vm = lima_vm_create(ldev);

Signed-off-by: Alban Browaeys <alban.browaeys@xxxxxxxxx>
---
 drivers/gpu/drm/lima/lima_device.c |  2 +-
 drivers/gpu/drm/lima/lima_drv.c    |  2 +-
 drivers/gpu/drm/lima/lima_vm.c     | 10 +++++++---
 drivers/gpu/drm/lima/lima_vm.h     |  3 ++-
 4 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/lima/lima_device.c b/drivers/gpu/drm/lima/lima_device.c
index 02cef0cea657..bd3afff0f44a 100644
--- a/drivers/gpu/drm/lima/lima_device.c
+++ b/drivers/gpu/drm/lima/lima_device.c
@@ -368,7 +368,7 @@ int lima_device_init(struct lima_device *ldev)
 	if (err)
 		goto err_out0;
 
-	ldev->empty_vm = lima_vm_create(ldev);
+	ldev->empty_vm = lima_vm_create(ldev, false);
 	if (!ldev->empty_vm) {
 		err = -ENOMEM;
 		goto err_out1;
diff --git a/drivers/gpu/drm/lima/lima_drv.c b/drivers/gpu/drm/lima/lima_drv.c
index 10fd9154cc46..ca09142e0ac1 100644
--- a/drivers/gpu/drm/lima/lima_drv.c
+++ b/drivers/gpu/drm/lima/lima_drv.c
@@ -219,7 +219,7 @@ static int lima_drm_driver_open(struct drm_device *dev, struct drm_file *file)
 	if (!priv)
 		return -ENOMEM;
 
-	priv->vm = lima_vm_create(ldev);
+	priv->vm = lima_vm_create(ldev, true);
 	if (!priv->vm) {
 		err = -ENOMEM;
 		goto err_out0;
diff --git a/drivers/gpu/drm/lima/lima_vm.c b/drivers/gpu/drm/lima/lima_vm.c
index 2b2739adc7f5..7f9775eefd78 100644
--- a/drivers/gpu/drm/lima/lima_vm.c
+++ b/drivers/gpu/drm/lima/lima_vm.c
@@ -197,7 +197,7 @@ u32 lima_vm_get_va(struct lima_vm *vm, struct lima_bo *bo)
 	return ret;
 }
 
-struct lima_vm *lima_vm_create(struct lima_device *dev)
+struct lima_vm *lima_vm_create(struct lima_device *dev, bool has_drm_mm)
 {
 	struct lima_vm *vm;
 
@@ -221,7 +221,10 @@ struct lima_vm *lima_vm_create(struct lima_device *dev)
 			goto err_out1;
 	}
 
-	drm_mm_init(&vm->mm, dev->va_start, dev->va_end - dev->va_start);
+	if (has_drm_mm) {
+		vm->has_drm_mm = true;
+		drm_mm_init(&vm->mm, dev->va_start, dev->va_end - dev->va_start);
+	}
 
 	return vm;
 
@@ -237,7 +240,8 @@ void lima_vm_release(struct kref *kref)
 	struct lima_vm *vm = container_of(kref, struct lima_vm, refcount);
 	int i;
 
-	drm_mm_takedown(&vm->mm);
+	if (vm->has_drm_mm)
+		drm_mm_takedown(&vm->mm);
 
 	for (i = 0; i < LIMA_VM_NUM_BT; i++) {
 		if (vm->bts[i].cpu)
diff --git a/drivers/gpu/drm/lima/lima_vm.h b/drivers/gpu/drm/lima/lima_vm.h
index 3a7c74822d8b..e7443f410d6d 100644
--- a/drivers/gpu/drm/lima/lima_vm.h
+++ b/drivers/gpu/drm/lima/lima_vm.h
@@ -30,6 +30,7 @@ struct lima_vm {
 	struct mutex lock;
 	struct kref refcount;
 
+	bool has_drm_mm;
 	struct drm_mm mm;
 
 	struct lima_device *dev;
@@ -43,7 +44,7 @@ void lima_vm_bo_del(struct lima_vm *vm, struct lima_bo *bo);
 
 u32 lima_vm_get_va(struct lima_vm *vm, struct lima_bo *bo);
 
-struct lima_vm *lima_vm_create(struct lima_device *dev);
+struct lima_vm *lima_vm_create(struct lima_device *dev, bool has_drm_mm);
 void lima_vm_release(struct kref *kref);
 
 static inline struct lima_vm *lima_vm_get(struct lima_vm *vm)
-- 
2.39.2