From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from perceval.ideasonboard.com (perceval.ideasonboard.com [213.167.242.64]) (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 68C56281503; Tue, 19 Aug 2025 14:55:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=213.167.242.64 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755615304; cv=none; b=eaKiu3mPO3vqKVtBR0clXquDNlpAnWgfVM0D9DMlXs2e6BfuEd2mmOrM1JK712B6oexu7LyyICe2BR8uYbk5mzieeOjWJgiqOrEFDW6wTQMk4y0AZ5mFYDVczOTU9pThJ+lKj0xjoIAAw498AgP6efvWzGc7quUOsZ5dEIff7Os= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755615304; c=relaxed/simple; bh=aym/MtJwNFxDBbjW3PypqoxF19bnG7z0x64ukaMHAqo=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=i1XgpXV6/sKuKmaEQtSDgVotWEIoXUntOjxfVXhTL64EW8snJIV1c3uCrN7+92Y39wljUsnWmDd+yazjGnPc8CRYk+74aPIbMMuKKYTgcM82SNNAxiB4VhkqirmD5mXgT7ytlEdRxZ6VqgJJR3/VIFGY3s0oHbh3wNu5tbVIobw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=ideasonboard.com; spf=pass smtp.mailfrom=ideasonboard.com; dkim=pass (1024-bit key) header.d=ideasonboard.com header.i=@ideasonboard.com header.b=a1/cUmhC; arc=none smtp.client-ip=213.167.242.64 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=ideasonboard.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=ideasonboard.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=ideasonboard.com header.i=@ideasonboard.com header.b="a1/cUmhC" Received: from [192.168.1.106] (mob-5-90-52-92.net.vodafone.it [5.90.52.92]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id 3045F3008; Tue, 19 Aug 2025 16:54:01 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1755615242; bh=aym/MtJwNFxDBbjW3PypqoxF19bnG7z0x64ukaMHAqo=; h=From:Date:Subject:References:In-Reply-To:To:Cc:From; b=a1/cUmhCsx2E2UpaXdOopanyybkEyD3OnjmMtqrmxHYRwGcX84rXTvMZn4HQBJidV ppQh60GslnL2sYK/jgttaTYB4l7BPgdoLQLYntGzBsVF9480KRkC1QyE+RCL/RilSu ev73XtwP1A8/nRjj4mESpcLK36QBtsrI4SP5bxIM= From: Jacopo Mondi Date: Tue, 19 Aug 2025 16:54:45 +0200 Subject: [PATCH v3 4/8] media: Documentation: uapi: Add V4L2 extensible parameters Precedence: bulk X-Mailing-List: linux-media@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20250819-extensible-parameters-validation-v3-4-9dc008348b30@ideasonboard.com> References: <20250819-extensible-parameters-validation-v3-0-9dc008348b30@ideasonboard.com> In-Reply-To: <20250819-extensible-parameters-validation-v3-0-9dc008348b30@ideasonboard.com> To: Dafna Hirschfeld , Laurent Pinchart , Keke Li , Mauro Carvalho Chehab , Heiko Stuebner , Dan Scally , Sakari Ailus Cc: linux-kernel@vger.kernel.org, linux-media@vger.kernel.org, linux-rockchip@lists.infradead.org, linux-arm-kernel@lists.infradead.org, Jacopo Mondi X-Mailer: b4 0.14.2 X-Developer-Signature: v=1; a=openpgp-sha256; l=5954; i=jacopo.mondi@ideasonboard.com; h=from:subject:message-id; bh=aym/MtJwNFxDBbjW3PypqoxF19bnG7z0x64ukaMHAqo=; b=owEBbQKS/ZANAwAKAXI0Bo8WoVY8AcsmYgBopJA75XlyPwtLgk4rj7RKxFlMq4i50NyL4UWfN uMar5i+H+OJAjMEAAEKAB0WIQS1xD1IgJogio9YOMByNAaPFqFWPAUCaKSQOwAKCRByNAaPFqFW PB65D/0Ufjf+cdMaGf2rKP0MKS9IihXbFbcpgKYGuVFjosg6pYYnmfMJq9heO7XBT2zwomLc2kq O3dsrjIXgBi9Ejy4m4rMv1zhEELBjNri/eFU1qcTGjTUXRCQ+SQyh/v3hTPDc/DAA1N+TlDtzPA 846aPpnpRH79ychydDlZxPwom6ndDDxcWjbmbuEeuUSpp2Yn0YnI1HI/fAIH/+HABS/+J+n+zlz w/9Ld/z9G3tpfZhwT/MwTrljzrFJIO1K/uZAOtNPwQgIykRaKH36Fa9ziqs8gCHHtM44eU6EHTx VsXKve5ceSRZCDcDKLBnKQVpwwaxcYdcz24cnO7m6+4WANBCWtKMl6zBESGj9XMGW08RztzRUj+ t7tpMffSODQL8EzQtYnA2hPOW/eEfdzdtS+0d9BPgh6x/LmTDxF3d2wfEa0GxV7fM3HKrOGnVJN pB+bvIoeqAS6wZBDCBnL0lIstzGLhn3RSSWF4faopw4qzJNZZrafNXstAD1cKjT5b4JTkvCpW66 ckd9EKxEl5t/eEgbDHGMOzJ0kmbXiJchdyibdko1aPPywUk1+7ZUwfwDMWqBK4zy5WQGOHFQyHP HsJQtX3goAUrPXloG/SQjX4g3PaYZfRU5da98CmrONfrZ071kYWoF0oePRDoCxC318aVtSRpF7m VJETJoZjFD7z/ig== X-Developer-Key: i=jacopo.mondi@ideasonboard.com; a=openpgp; fpr=72392EDC88144A65C701EA9BA5826A2587AD026B Add documentation for extensible parameters format to the V4L2 userspace API documentation. Reviewed-by: Daniel Scally Signed-off-by: Jacopo Mondi --- .../media/v4l/extensible-parameters.rst | 89 ++++++++++++++++++++++ .../userspace-api/media/v4l/meta-formats.rst | 1 + MAINTAINERS | 1 + 3 files changed, 91 insertions(+) diff --git a/Documentation/userspace-api/media/v4l/extensible-parameters.rst b/Documentation/userspace-api/media/v4l/extensible-parameters.rst new file mode 100644 index 0000000000000000000000000000000000000000..c4caa5c1df991d4dd91f986571db55135d15204a --- /dev/null +++ b/Documentation/userspace-api/media/v4l/extensible-parameters.rst @@ -0,0 +1,89 @@ +.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later + +.. _extensible-parameters: + +********************************** + V4L2 extensible parameters format +********************************** + +ISP configuration +================= + +ISP configuration parameters are computed by userspace and programmed into a +*parameters buffer* which is queued to the ISP driver on a per-frame basis. The +layout of the *parameters buffer* generally reflects the ISP peripheral +registers layout and is, for this reason, platform specific. + +The ISP configuration parameters are passed to the ISP driver through a metadata +output video node, using the :c:type:`v4l2_meta_format` interface. Each ISP +driver defines a metadata format that implements the configuration parameters +layout. + +Metadata output formats that describe ISP configuration parameters are most of +the time realized by implementing C structures that reflect the registers layout +and gets populated by userspace before queueing the buffer to the ISP. Each +C structure usually corresponds to one ISP *processing block*, with each block +implementing one of the ISP supported features. + +The uAPI/ABI problem +-------------------- + +By upstreaming data types that describe the configuration parameters layout, +driver developers make them part of the Linux kernel ABI. As it sometimes +happens for most peripherals in Linux, ISP drivers development is often an +iterative process, where sometimes not all the hardware features are supported +in the first version that lands in the kernel, and some parts of the interface +have to later be modified for bug-fixes or improvements. + +If any later bug-fix/improvement requires changes to the metadata output format, +this is considered an ABI-breakage that is strictly forbidden by the Linux +kernel policies. For this reason, each new iteration of an ISP driver support +would require defining a new metadata output format, implying that drivers have +to be made ready to handle several different configuration formats. + +A new set of metadata output formats has then to be defined, with the design +goals of being: + +- Extensible: new features can be added later on without breaking the existing + interface +- Versioned: different versions of the format can be defined without + breaking the existing interface + +The extensible parameters format +================================ + +Extensible configuration formats are realized by a defining a single C structure +that contains a few control parameters and a binary buffer where userspace +programs a variable number of *ISP configuration blocks* data. + +The generic :c:type:`v4l2_params_buffer` defines a base type that each driver +can use by properly sizing the data buffer array. + +Each *ISP configuration block* is identified by an header and contains the +parameters for that specific block. + +The generic :c:type:`v4l2_params_block_header` defines a base type that each +driver can re-use as it is or extend appropriately. + +Userspace applications program in the control buffer only the parameters of the +ISP whose configuration has changed for the next frame. The ISP driver parses +the configuration parameters and apply them to the hardware register. + +Any further development that happens after the ISP driver has been merged in +Linux and which requires supporting new ISP features can be implemented by +adding new blocks definition without invalidating the existing ones. Similarly, +any change to the existing ISP configuration blocks can be handled by versioning +them, again without invalidating the existing ones. + +Implementations +--------------- + +ISP drivers that define an extensible parameters metadata output format: + +- :ref:`RkISP1 ` +- :ref:`Amlogic C3 ISP ` + +V4L2 extensible parameters uAPI data types +========================================== + +.. kernel-doc:: include/uapi/linux/media/v4l2-extensible-params.h diff --git a/Documentation/userspace-api/media/v4l/meta-formats.rst b/Documentation/userspace-api/media/v4l/meta-formats.rst index 0de80328c36bf148051a19abe9e5241234ddfe5c..b900ed6af7bd9ad49baf7b5a9eef9423f8abfbcb 100644 --- a/Documentation/userspace-api/media/v4l/meta-formats.rst +++ b/Documentation/userspace-api/media/v4l/meta-formats.rst @@ -12,6 +12,7 @@ These formats are used for the :ref:`metadata` interface only. .. toctree:: :maxdepth: 1 + extensible-parameters metafmt-c3-isp metafmt-d4xx metafmt-generic diff --git a/MAINTAINERS b/MAINTAINERS index 67216d1e92d7ac81617bb3c4329e4096aa205706..91df04e5d9022ccf2aea4445247369a8b86a4264 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -26384,6 +26384,7 @@ V4L2 EXTENSIBLE PARAMETERS FORMAT M: Jacopo Mondi L: linux-media@vger.kernel.org S: Maintained +F: Documentation/userspace-api/media/v4l/extensible-parameters.rst F: include/uapi/linux/media/v4l2-extensible-params.h VF610 NAND DRIVER -- 2.50.1