From nobody Sat Apr 11 17:23:10 2026 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 B40A8C6FD20 for ; Wed, 8 Mar 2023 13:55:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231842AbjCHNzl (ORCPT ); Wed, 8 Mar 2023 08:55:41 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54886 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231848AbjCHNyb (ORCPT ); Wed, 8 Mar 2023 08:54:31 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9F49491B48; Wed, 8 Mar 2023 05:53:24 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 94927B81CE2; Wed, 8 Mar 2023 13:53:23 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4587AC4339C; Wed, 8 Mar 2023 13:53:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1678283602; bh=zbALlWFHvbSHmi7+KHrV5xNme8KL939BcCxb4rMePOc=; h=From:To:Cc:Subject:Date:From; b=Eah7eUmAgpi2Ny1duKjelRbSeZf7gS17+heVLO4seegtn4fsxTqYAn/OPtC3kP8UQ /RVr0luwFzl7yo8dFcja41MXPsjO2oM9Dvc2onhVrkNa7hiiZQr1yjCQXBb4pb2glg ghW8sgeqIrrnrT30mFR65ggXC6UBgVLNm/LmSfUS4Jjl+m8gWaO8Ny2tuKljpkNOUX rpSjV5c9YSQ9C1dLD6EdIU+Cq1QnBwX16kToo9YmyvCMV35y/W1GIPHguKp0dfQgSW KhrFdbKJOL+YNBnAsxgvrtQwWQ1aHFbcqspDtCLuLNK/ArDV0Sn//b5B/NvVyZ0ip3 ZYBZuFEbJf1uA== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Paul Elder , Laurent Pinchart , Jacopo Mondi , Jai Luthra , Sakari Ailus , Mauro Carvalho Chehab , Sasha Levin , slongerbeam@gmail.com, linux-media@vger.kernel.org Subject: [PATCH AUTOSEL 4.19] media: ov5640: Fix analogue gain control Date: Wed, 8 Mar 2023 08:53:19 -0500 Message-Id: <20230308135319.2927539-1-sashal@kernel.org> X-Mailer: git-send-email 2.39.2 MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" From: Paul Elder [ Upstream commit afa4805799c1d332980ad23339fdb07b5e0cf7e0 ] 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]=3D0, 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]=3D1, 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 Signed-off-by: Sakari Ailus Signed-off-by: Mauro Carvalho Chehab Signed-off-by: Sasha Levin --- 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 aa9c0b7ee7a22..31b26b18e5251 100644 --- a/drivers/media/i2c/ov5640.c +++ b/drivers/media/i2c/ov5640.c @@ -2447,7 +2447,7 @@ static int ov5640_init_controls(struct ov5640_dev *se= nsor) /* Auto/manual gain */ ctrls->auto_gain =3D v4l2_ctrl_new_std(hdl, ops, V4L2_CID_AUTOGAIN, 0, 1, 1, 1); - ctrls->gain =3D v4l2_ctrl_new_std(hdl, ops, V4L2_CID_GAIN, + ctrls->gain =3D v4l2_ctrl_new_std(hdl, ops, V4L2_CID_ANALOGUE_GAIN, 0, 1023, 1, 0); =20 ctrls->saturation =3D v4l2_ctrl_new_std(hdl, ops, V4L2_CID_SATURATION, --=20 2.39.2