From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E9AD32BE7A7; Tue, 30 Sep 2025 07:30:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759217460; cv=none; b=hvM3SS+Yj6LEVY8KlXY179fBgv2kSoa2E8YhPJVfZdbyiudKrMzkb4tWQQzNvcW844lD/3znJ/jdbsMAhltFFISazm+Ulya8cqlP4dAQCAVkgyx3gN7xY4fgAZmJdI0YFr+9DLlxij5z9lz57fvjCv4F+mEVDQpKq5iEc0dVa/k= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759217460; c=relaxed/simple; bh=ViYV65AZcIp1SdYamrftx+FDdb1Xx0jipTI6UYaCuf0=; h=Message-ID:Date:MIME-Version:From:Subject:To:Cc:References: In-Reply-To:Content-Type; b=G4peUf3f4tfzzeMjIgStqWkOvP8tEVaxJrMFFfNPRJ4+fdicklL2LIg900XLI/lMwoLxKYIn5Ez+80RvD6jg4m8VjhQ5CcBWS/lfLLi3zg1AAIHMfljU15/3HROx9N/2KXra/i0k5NDgqo0QjGlIN0JZvwOD2RdCeYwPzeS6U34= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Hs/u04B5; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Hs/u04B5" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4492EC4CEF0; Tue, 30 Sep 2025 07:30:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1759217459; bh=ViYV65AZcIp1SdYamrftx+FDdb1Xx0jipTI6UYaCuf0=; h=Date:From:Subject:To:Cc:References:In-Reply-To:From; b=Hs/u04B5gasxxeQWSu/TKDI0cn1EA6jKRL4QCmDEMNEC/jCupmRQ5DFOzlXLsP5N3 Si2MDPZ8UdbEQ0e8RTrDEN7wONVTPnzOIpITiZec3ghZtJbeUqUdMm4X07AyrwpymF Y50C4EKH5VQykf6DDpfzsAubW4mL5O3xgnFr4VKRbtg30MhDMr0ausLTAeqKVskiqv lxE/rpY/XDvmyq0FfWYnUqjv8vhRNaQdmLaLo9TIrPTYAPvtGCesO2DBUIvQvc1NHV UbU4ankKxlHwUGhxjLZhVqnFQXFTJ3rNHBRUK/F1TSHFqrSC79FYIQ9lsJIkAfhSK2 JY++8moJFSbyQ== Message-ID: <006000c4-7ecd-474f-ac0c-90c7b0606506@kernel.org> Date: Tue, 30 Sep 2025 09:30:55 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird From: Hans Verkuil Subject: Re: [PATCH v2 02/10] media: v4l2-dev: Add support for try state To: Jai Luthra , Hans Verkuil , Jacopo Mondi , Laurent Pinchart , Mauro Carvalho Chehab , Sakari Ailus , Tomi Valkeinen , linux-media@vger.kernel.org Cc: Ricardo Ribalda , Laurent Pinchart , Ma Ke , Bartosz Golaszewski , linux-kernel@vger.kernel.org References: <20250919-vdev-state-v2-0-b2c42426965c@ideasonboard.com> <20250919-vdev-state-v2-2-b2c42426965c@ideasonboard.com> <3eef0f98-c34a-4b67-97f4-d60cd1eab8ad@kernel.org> <16f45860-923b-4b5d-995e-0729d0479752@kernel.org> <175916253442.2234821.5624749898039510125@freya> Content-Language: en-US, nl In-Reply-To: <175916253442.2234821.5624749898039510125@freya> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 29/09/2025 18:15, Jai Luthra wrote: > Hi Hans, > > Quoting Hans Verkuil (2025-09-22 13:28:26) >> On 22/09/2025 09:52, Hans Verkuil wrote: >>> On 19/09/2025 11:55, Jai Luthra wrote: >>>> Format negotiation performed via the TRY_FMT ioctl should only affect >>>> the temporary context of a specific filehandle, not the active state >>>> stored in the video device structure. To support this distinction, we >>>> need separate storage for try and active states. >>>> >>>> Introduce an enum to distinguish between these two state types and store >>>> the try state in struct v4l2_fh instead of the video device structure. >>>> The try state is allocated during file handle initialization in >>>> v4l2_fh_init() and released in v4l2_fh_exit(). >>> >>> There is a major difference between TRY in video devices and TRY in subdev >>> devices: TRY for video devices is not persistent, i.e. it doesn't need to >>> be stored anywhere since nobody will be using that information. >>> > > Yes, the v4l2 format sent with VIDIOC_TRY_FMT is currently not stored by > the drivers, but simply modified and returned back to userspace. From the > userspace point of view, that should still work the same way with this > series. > > The drivers will get access to the correct state (active) for internal use > through framework helpers (that will be introduced in next revision), so > the try state doesn't have any real "use" today. > >>> If the plan is to change that in later patch series, then that should be >>> very clearly stated. And I think I would need to know the details of those >>> future plans before I can OK this. >>> >>> So how is this try state intended to be used in the future? >> >> Follow-up: if there are no plans to change/enhance the VIDIOC_TRY_FMT semantics, >> then I don't really see the point of this since there is no need to store this >> information. > > There are no plans to change the userspace side of this. The main > motivation to allocate and keep a try state in the framework is to simplify > the driver implementation. A single function can serve as both s_fmt and > try_fmt ioctl handler, and operate on the passed state argument without > caring if it will be applied on the device or just for negotiation. > > In future, drivers may subclass the state with their device specific data, > so that nothing tied to the hardware state is stored in the driver > structures directly, but I don't see why drivers will need to inspect TRY > formats. I think having an unused try state is a bad idea and really confusing. Especially because for subdevices the try state is actually used, so for normal devices you would automatically expect the same thing when you see a try state. You should reconsider this approach. Regards, Hans