[PATCH v2] drm/panthor: Fix couple of NULL vs IS_ERR() bugs

[Harshit Mogalapalli <harshit.m.mogalapalli@xxxxxxxxxx>]

1. The devm_drm_dev_alloc() function returns error pointers.
   Update the error handling to check for error pointers instead of NULL.
2. Currently panthor_vm_get_heap_pool() returns both ERR_PTR() and
   NULL(when create is false and if there is no poool attached to the
   VM)
	- Change the function to return error pointers, when pool is
	  NULL return -ENOENT
	- Also handle the callers to check for IS_ERR() on failure.

Fixes: 4bdca1150792 ("drm/panthor: Add the driver frontend block")
Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@xxxxxxxxxx>
---
This is spotted by smatch and the patch is only compile tested

v1->v2: Fix the function panthor_vm_get_heap_pool() to only return error
pointers and handle the caller sites [Suggested by Boris Brezillon]
	- Also merge these IS_ERR() vs NULL bugs into same patch
---
 drivers/gpu/drm/panthor/panthor_drv.c   | 6 +++---
 drivers/gpu/drm/panthor/panthor_mmu.c   | 2 ++
 drivers/gpu/drm/panthor/panthor_sched.c | 2 +-
 3 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/panthor/panthor_drv.c b/drivers/gpu/drm/panthor/panthor_drv.c
index 11b3ccd58f85..c8374cd4a30d 100644
--- a/drivers/gpu/drm/panthor/panthor_drv.c
+++ b/drivers/gpu/drm/panthor/panthor_drv.c
@@ -1090,8 +1090,8 @@ static int panthor_ioctl_tiler_heap_destroy(struct drm_device *ddev, void *data,
 		return -EINVAL;
 
 	pool = panthor_vm_get_heap_pool(vm, false);
-	if (!pool) {
-		ret = -EINVAL;
+	if (IS_ERR(pool)) {
+		ret = PTR_ERR(pool);
 		goto out_put_vm;
 	}
 
@@ -1385,7 +1385,7 @@ static int panthor_probe(struct platform_device *pdev)
 
 	ptdev = devm_drm_dev_alloc(&pdev->dev, &panthor_drm_driver,
 				   struct panthor_device, base);
-	if (!ptdev)
+	if (IS_ERR(ptdev))
 		return -ENOMEM;
 
 	platform_set_drvdata(pdev, ptdev);
diff --git a/drivers/gpu/drm/panthor/panthor_mmu.c b/drivers/gpu/drm/panthor/panthor_mmu.c
index fdd35249169f..e1285cdb09ff 100644
--- a/drivers/gpu/drm/panthor/panthor_mmu.c
+++ b/drivers/gpu/drm/panthor/panthor_mmu.c
@@ -1893,6 +1893,8 @@ struct panthor_heap_pool *panthor_vm_get_heap_pool(struct panthor_vm *vm, bool c
 			vm->heaps.pool = panthor_heap_pool_get(pool);
 	} else {
 		pool = panthor_heap_pool_get(vm->heaps.pool);
+		if (!pool)
+			pool = ERR_PTR(-ENOENT);
 	}
 	mutex_unlock(&vm->heaps.lock);
 
diff --git a/drivers/gpu/drm/panthor/panthor_sched.c b/drivers/gpu/drm/panthor/panthor_sched.c
index 5f7803b6fc48..617df2b980d0 100644
--- a/drivers/gpu/drm/panthor/panthor_sched.c
+++ b/drivers/gpu/drm/panthor/panthor_sched.c
@@ -1343,7 +1343,7 @@ static int group_process_tiler_oom(struct panthor_group *group, u32 cs_id)
 	if (unlikely(csg_id < 0))
 		return 0;
 
-	if (!heaps || frag_end > vt_end || vt_end >= vt_start) {
+	if (IS_ERR(heaps) || frag_end > vt_end || vt_end >= vt_start) {
 		ret = -EINVAL;
 	} else {
 		/* We do the allocation without holding the scheduler lock to avoid
-- 
2.39.3