From patchwork Mon Nov 28 08:02:01 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Laurent Pinchart X-Patchwork-Id: 629126 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 620A3C4332F for ; Mon, 28 Nov 2022 08:02:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229744AbiK1ICU (ORCPT ); Mon, 28 Nov 2022 03:02:20 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56428 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229730AbiK1ICT (ORCPT ); Mon, 28 Nov 2022 03:02:19 -0500 Received: from perceval.ideasonboard.com (perceval.ideasonboard.com [213.167.242.64]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2A219B7EC for ; Mon, 28 Nov 2022 00:02:18 -0800 (PST) Received: from pendragon.ideasonboard.com (62-78-145-57.bb.dnainternet.fi [62.78.145.57]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id A788C501; Mon, 28 Nov 2022 09:02:16 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1669622536; bh=sNu2YI98bdKcNFr62WC7xOiNkkGM1N19cIqCl1s6NyU=; h=From:To:Cc:Subject:Date:From; b=GX9yLtGa61xJohUWE64JQsS5UM1o4LOVOt5bxygn5OOEZVMe31tJvkT5fOu5LwQh3 0namRYDA21cHIbMO0ODIogbjzOfxS2GXquw0/Ra6DG+8r9f0W7IENaYSLyCoUr2KUn SqhHTpZemtFZ+lI21riKx3UaaggutLF8uq2Kd5po= From: Laurent Pinchart To: linux-media@vger.kernel.org Cc: Jacopo Mondi , Sakari Ailus , Paul Elder , Steve Longerbeam , hugues.fruchet@st.com, prabhakar.mahadev-lad.rj@bp.renesas.com, aford173@gmail.com, festevam@gmail.com, eddy.khan@vergesense.com, paul.kocialkowski@bootlin.com, eugen.hristev@microchip.com Subject: [PATCH v2] media: ov5640: Fix analogue gain control Date: Mon, 28 Nov 2022 10:02:01 +0200 Message-Id: <20221128080201.15104-1-laurent.pinchart@ideasonboard.com> X-Mailer: git-send-email 2.37.4 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org From: Paul Elder Gain control is badly documented in publicly available (including leaked) documentation. There is an AGC pre-gain in register 0x3a13, expressed as a 6-bit value (plus an enable bit in bit 6). The driver hardcodes it to 0x43, which one application note states is equal to x1.047. The documentation also states that 0x40 is equel to x1.000. The pre-gain thus seems to be expressed as in 1/64 increments, and thus ranges from x1.00 to x1.984. What the pre-gain does is however unspecified. There is then an AGC gain limit, in registers 0x3a18 and 0x3a19, expressed as a 10-bit "real gain format" value. One application note sets it to 0x00f8 and states it is equal to x15.5, so it appears to be expressed in 1/16 increments, up to x63.9375. The manual gain is stored in registers 0x350a and 0x350b, also as a 10-bit "real gain format" value. It is documented in the application note as a Q6.4 values, up to x63.9375. One version of the datasheet indicates that the sensor supports a digital gain: The OV5640 supports 1/2/4 digital gain. Normally, the gain is controlled automatically by the automatic gain control (AGC) block. It isn't clear how that would be controlled manually. There appears to be no indication regarding whether the gain controlled through registers 0x350a and 0x350b is an analogue gain only or also includes digital gain. The words "real gain" don't necessarily mean "combined analogue and digital gains". Some OmniVision sensors (such as the OV8858) are documented as supoprting different formats for the gain values, selectable through a register bit, and they are called "real gain format" and "sensor gain format". For that sensor, we have (one of) the gain registers documented as 0x3503[2]=0, gain[7:0] is real gain format, where low 4 bits are fraction bits, for example, 0x10 is 1x gain, 0x28 is 2.5x gain If 0x3503[2]=1, gain[7:0] is sensor gain format, gain[7:4] is coarse gain, 00000: 1x, 00001: 2x, 00011: 4x, 00111: 8x, gain[7] is 1, gain[3:0] is fine gain. For example, 0x10 is 1x gain, 0x30 is 2x gain, 0x70 is 4x gain (The second part of the text makes little sense) "Real gain" may thus refer to the combination of the coarse and fine analogue gains as a single value. The OV5640 0x350a and 0x350b registers thus appear to control analogue gain. The driver incorrectly uses V4L2_CID_GAIN as V4L2 has a specific control for analogue gain, V4L2_CID_ANALOGUE_GAIN. Use it. If registers 0x350a and 0x350b are later found to control digital gain as well, the driver could then restrict the range of the analogue gain control value to lower than x64 and add a separate digital gain control. Signed-off-by: Paul Elder Signed-off-by: Laurent Pinchart Reviewed-by: Jacopo Mondi Reviewed-by: Jai Luthra --- drivers/media/i2c/ov5640.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/media/i2c/ov5640.c b/drivers/media/i2c/ov5640.c index 2d740397a5d4..c65c391bc1eb 100644 --- a/drivers/media/i2c/ov5640.c +++ b/drivers/media/i2c/ov5640.c @@ -3458,7 +3458,7 @@ static int ov5640_init_controls(struct ov5640_dev *sensor) /* Auto/manual gain */ ctrls->auto_gain = v4l2_ctrl_new_std(hdl, ops, V4L2_CID_AUTOGAIN, 0, 1, 1, 1); - ctrls->gain = v4l2_ctrl_new_std(hdl, ops, V4L2_CID_GAIN, + ctrls->gain = v4l2_ctrl_new_std(hdl, ops, V4L2_CID_ANALOGUE_GAIN, 0, 1023, 1, 0); ctrls->saturation = v4l2_ctrl_new_std(hdl, ops, V4L2_CID_SATURATION,