Re: What should bridge drivers use instead of __v4l2_subdev_state_alloc()?
From: Tomi Valkeinen
Date: Sun Nov 08 2026 - 11:06:04 EST
Hi,
On 08/11/2026 12:25, Laurent Pinchart wrote:
On Sat, Nov 07, 2026 at 05:31:06PM -0800, DelaySystem wrote:I think converting to MC is the answer. At least for a staging driver.
Hello,
While working on drivers/staging/media/tegra-video I ran into the FIXME
above __tegra_channel_try_format() in vi.c (added by commit 40aaab9d773b
in 2022):
/* FIXME: Drop this call, drivers are not supposed to use
* __v4l2_subdev_state_alloc(). */
The driver needs a scratch TRY state to negotiate formats with the remote
sensor subdev from video-node ioctl context, where no subdev file handle
exists. I looked for the intended replacement, but:
- there is no non-dunder allocator in drivers/media or include/media;
- v4l2_subdev_call_state_try() is documented for legacy non-MC drivers
only, has no in-tree users, and allocates one state per call, while the
driver needs one state across enum_frame_size + set_fmt + get_crop;
- the active-state APIs have the wrong semantics here, since try_fmt must
not disturb ACTIVE state;
- the same FIXME is still present in mainline vsp1 and staging atomisp,
and mainline stm32-dcmi still calls the dunder directly, with (as far
as I can tell) zero conversions since the 2022 rename.
So my question: is a new core helper the intended direction for the
bridge-driver scratch-TRY-state case, and if so, is there any guidance
on the shape it should take? Or is there an existing pattern I missed?
If a new helper is the answer, I am happy to implement it and convert
the in-tree users.
No, that's not the answer.
Tomi