Since a recent fix the mtk_jpeg_release function cancels any pending
or running work present in the driver workqueue using
cancel_work_sync function.
Currently, only the multicore based variants use this workqueue and they
have the jpeg_worker platform data field initialized with a workqueue
callback function. For the others, this field value remain NULL by
default.
The cancel_work_sync function is unconditionally called in
mtk_jpeg_release function, even for the variants that do not use the
workqueue. This call generates a WARN_ON print in __flush_work because
the workqueue callback function presence check fails in __flush_work
function (used by cancel_work_sync).

So, to avoid these warnings, call cancel_work_sync only if a workqueue
callback is defined in platform data.

Fixes: 34c519feef3e ("media: mtk-jpeg: fix use-after-free in release path due to uncancelled work")
Signed-off-by: Louis-Alexis Eyraud <louisalexis.eyraud@collabora.com>
---
Patch to fix the following warning that occurs on boards such as
Mediatek Genio 510-EVK:
```
WARNING: kernel/workqueue.c:4291 at __flush_work+0x320/0x340, CPU#1:
  v4l_id/409
...
Call trace:
 __flush_work+0x320/0x340 (P)
 cancel_work_sync+0x6c/0x9c
 mtk_jpeg_release+0x2c/0x84 [mtk_jpeg]
 v4l2_release+0x8c/0xe8 [videodev]
 __fput+0xcc/0x2e0
 fput_close_sync+0x40/0x100
 __arm64_sys_close+0x38/0x7c
 invoke_syscall+0x54/0x10c
 el0_svc_common.constprop.0+0xc0/0xe0
 do_el0_svc+0x1c/0x34
 el0_svc+0x34/0x108
 el0t_64_sync_handler+0xa0/0xf0
 el0t_64_sync+0x198/0x19c
---[ end trace 0000000000000000 ]---
```

It is based on linux-next (tag next-20260331) and has been tested on
Mediatek Genio 510-EVK (mt8390) and 1200-EVK (mt8395) boards.
---
 drivers/media/platform/mediatek/jpeg/mtk_jpeg_core.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/media/platform/mediatek/jpeg/mtk_jpeg_core.c b/drivers/media/platform/mediatek/jpeg/mtk_jpeg_core.c
index 8c684756d5fc2524da3a67f67f0fdda894b676fc..d147ec48308110ae8520662e182dc0445447d8d0 100644
--- a/drivers/media/platform/mediatek/jpeg/mtk_jpeg_core.c
+++ b/drivers/media/platform/mediatek/jpeg/mtk_jpeg_core.c
@@ -1202,7 +1202,8 @@ static int mtk_jpeg_release(struct file *file)
 	struct mtk_jpeg_dev *jpeg = video_drvdata(file);
 	struct mtk_jpeg_ctx *ctx = mtk_jpeg_file_to_ctx(file);
 
-	cancel_work_sync(&ctx->jpeg_work);
+	if (jpeg->variant->jpeg_worker)
+		cancel_work_sync(&ctx->jpeg_work);
 	mutex_lock(&jpeg->lock);
 	v4l2_m2m_ctx_release(ctx->fh.m2m_ctx);
 	v4l2_ctrl_handler_free(&ctx->ctrl_hdl);

---
base-commit: e5da3eef8dadab4e98b228725ca8948edd9d601f
change-id: 20260401-mtk-jpeg-release-issue-d8921970a250

Best regards,
-- 
Louis-Alexis Eyraud <louisalexis.eyraud@collabora.com>