From patchwork Mon Jul 10 13:22:40 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jacopo Mondi X-Patchwork-Id: 13307131 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D7BCFEB64D9 for ; Mon, 10 Jul 2023 13:23:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231637AbjGJNXL (ORCPT ); Mon, 10 Jul 2023 09:23:11 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36958 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231320AbjGJNXJ (ORCPT ); Mon, 10 Jul 2023 09:23:09 -0400 Received: from perceval.ideasonboard.com (perceval.ideasonboard.com [IPv6:2001:4b98:dc2:55:216:3eff:fef7:d647]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D937BE2 for ; Mon, 10 Jul 2023 06:23:04 -0700 (PDT) Received: from uno.LocalDomain (93-61-96-190.ip145.fastwebnet.it [93.61.96.190]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id 179FDDA7; Mon, 10 Jul 2023 15:22:07 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1688995327; bh=QKpNeSKW5e8AbrpNtPSuMYB/au8vcmPe2kyEIMgFs1U=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=nLLOmg5Y8lJU0JjR+G9pqAFHvIOuSrvaH/bPECJbbI0bD0GHD/UdYhUDUGJg+h3on DumMjCSY1K+H4hgXVbs96N+fRN0z0jewcYPIjhKt1riYfLuHE5IjBFmyKMAnD7pplW /y8hpi93pO1UHq8o5FUYGk1OwBTSgNODJ2kall20= From: Jacopo Mondi To: linux-media@vger.kernel.org Cc: Jacopo Mondi , Hans Verkuil , Sakari Ailus , Laurent Pinchart , Dave Stevenson Subject: [PATCH v3 2/2] Documentation: v4l: Exposure/gain for camera sensor Date: Mon, 10 Jul 2023 15:22:40 +0200 Message-Id: <20230710132240.7864-3-jacopo.mondi@ideasonboard.com> X-Mailer: git-send-email 2.40.1 In-Reply-To: <20230710132240.7864-1-jacopo.mondi@ideasonboard.com> References: <20230710132240.7864-1-jacopo.mondi@ideasonboard.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org Document the suggested way to exposure controls for exposure and gain for camera sensor drivers. Signed-off-by: Jacopo Mondi Reviewed-by: Dave Stevenson --- .../driver-api/media/camera-sensor.rst | 27 +++++++++++++++++++ 1 file changed, 27 insertions(+) diff --git a/Documentation/driver-api/media/camera-sensor.rst b/Documentation/driver-api/media/camera-sensor.rst index cd915ca119ea..67fe77b1edb9 100644 --- a/Documentation/driver-api/media/camera-sensor.rst +++ b/Documentation/driver-api/media/camera-sensor.rst @@ -189,3 +189,30 @@ the ``V4L2_CID_VFLIP`` and ``V4L2_CID_HFLIP`` controls with the a flip can potentially change the output buffer content layout. Flips should also be taken into account when enumerating and handling media bus formats on the camera sensor source pads. + +Exposure and Gain Control +------------------------- + +Camera sensor drivers that allow applications to control the image exposure +and gain should do so by exposing dedicated controls to applications. + +Exposure time is controlled by registering the ``V4L2_CID_EXPOSURE`` control. +The control definition does not specify a unit to allow maximum flexibility +for multiple device types, but when used for camera sensor drivers it should be +expressed in unit of lines whenever possible. + +To convert lines into units of time, the total line length (visible and +not visible pixels) has to be divided by the pixel rate:: + + line duration = total line length / pixel rate + = (image width + horizontal blanking) / pixel rate + +Camera sensor driver should try whenever possible to distinguish between the +analogue and digital gain control functions. Analogue gain is a multiplication +factor applied to all color channels on the pixel array before they get +converted into the digital domain. It should be made controllable by +registering the ``V4L2_CID_ANALOGUE_GAIN`` control, expressed as a device +specific gain code. Digital gain control is optional and should be exposed to +applications by registering ``V4L2_CID_DIGITAL_GAIN``. Camera sensor drivers are +discouraged from using ``V4L2_CID_GAIN`` as it doesn't allow differentiation of +analogue vs digital gain.