drm/panthor: Don't use virt_to_pfn()

virt_to_pfn() isn't available on x86 (except to xen) so breaks
COMPILE_TEST builds. Avoid its use completely by instead storing the
struct page pointer allocated in panthor_device_init() and using
page_to_pfn() instead.
Signed-off-by: Steven Price <steven.price@arm.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240318145119.368582-1-steven.price@arm.com

drivers/gpu/drm/panthor/panthor_device.c

@@ -151,11 +151,12 @@ static bool panthor_device_is_initialized(struct panthor_device *ptdev)
 
 static void panthor_device_free_page(struct drm_device *ddev, void *data)
 {
-	free_page((unsigned long)data);
+	__free_page(data);
 }
 
 int panthor_device_init(struct panthor_device *ptdev)
 {
+	u32 *dummy_page_virt;
 	struct resource *res;
 	struct page *p;
 	int ret;
@@ -176,7 +177,8 @@ int panthor_device_init(struct panthor_device *ptdev)
 	if (!p)
 		return -ENOMEM;
 
-	ptdev->pm.dummy_latest_flush = page_address(p);
+	ptdev->pm.dummy_latest_flush = p;
+	dummy_page_virt = page_address(p);
 	ret = drmm_add_action_or_reset(&ptdev->base, panthor_device_free_page,
 				       ptdev->pm.dummy_latest_flush);
 	if (ret)
@@ -188,7 +190,7 @@ int panthor_device_init(struct panthor_device *ptdev)
 	 * happens while the dummy page is mapped. Zero cannot be used because
 	 * that means 'always flush'.
 	 */
-	*ptdev->pm.dummy_latest_flush = 1;
+	*dummy_page_virt = 1;
 
 	INIT_WORK(&ptdev->reset.work, panthor_device_reset_work);
 	ptdev->reset.wq = alloc_ordered_workqueue("panthor-reset-wq", 0);
@@ -364,7 +366,7 @@ static vm_fault_t panthor_mmio_vm_fault(struct vm_fault *vmf)
 		if (active)
 			pfn = __phys_to_pfn(ptdev->phys_addr + CSF_GPU_LATEST_FLUSH_ID);
 		else
-			pfn = virt_to_pfn(ptdev->pm.dummy_latest_flush);
+			pfn = page_to_pfn(ptdev->pm.dummy_latest_flush);
 		break;
 
 	default:

drivers/gpu/drm/panthor/panthor_device.h

@@ -160,7 +160,7 @@ struct panthor_device {
 		 * Used to replace the real LATEST_FLUSH page when the GPU
 		 * is suspended.
 		 */
-		u32 *dummy_latest_flush;
+		struct page *dummy_latest_flush;
 	} pm;
 };