From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-12.4 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C5B6FC433E7 for ; Thu, 15 Oct 2020 19:52:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5F0B920708 for ; Thu, 15 Oct 2020 19:52:09 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=ideasonboard.com header.i=@ideasonboard.com header.b="XImvr/bA" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2391970AbgJOTwI (ORCPT ); Thu, 15 Oct 2020 15:52:08 -0400 Received: from perceval.ideasonboard.com ([213.167.242.64]:39764 "EHLO perceval.ideasonboard.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390610AbgJOTwH (ORCPT ); Thu, 15 Oct 2020 15:52:07 -0400 Received: from [192.168.0.20] (cpc89244-aztw30-2-0-cust3082.18-1.cable.virginm.net [86.31.172.11]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id 046C2556; Thu, 15 Oct 2020 21:52:03 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1602791524; bh=tSiZOoMQ5d809be+4Lr3m5yOAWnqK22Ya15Q63vM+lk=; h=Reply-To:Subject:To:Cc:References:From:Date:In-Reply-To:From; b=XImvr/bA/3C4KLjFdov9rgttrOSWQfBuSrV7vuG1n2hcZgxh0pu/zd3SXjGoRGnjo VBYmzfmBYdA4jVUhBCTjvQ+mLwp1NauIEpkOKTiMcDAeEusVLwHQqELJHBSlMrMO2K Dl+x9AJoz3zP8ZC7jPYJphn8TajiHPrvJfo2JmdE= Reply-To: kieran.bingham+renesas@ideasonboard.com Subject: Re: [PATCH v2 5/7] media: i2c: max9286: Configure reverse channel amplitude To: Jacopo Mondi , laurent.pinchart+renesas@ideasonboard.com, niklas.soderlund+renesas@ragnatech.se Cc: linux-media@vger.kernel.org, linux-renesas-soc@vger.kernel.org, linux-kernel@vger.kernel.org, Hyun Kwon , Manivannan Sadhasivam References: <20201015182710.54795-1-jacopo+renesas@jmondi.org> <20201015182710.54795-6-jacopo+renesas@jmondi.org> From: Kieran Bingham Organization: Ideas on Board Message-ID: Date: Thu, 15 Oct 2020 20:52:01 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20201015182710.54795-6-jacopo+renesas@jmondi.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-GB Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Jacopo, On 15/10/2020 19:27, Jacopo Mondi wrote: > Adjust reverse channel amplitude according to the presence of > the 'high-threshold" DTS property. > > If no high threshold compensation is required, start with a low > amplitude (100mV) and increase it after the remote serializers > have probed and have enabled noise immunity on their reverse > channels. > > If high threshold compensation is required, configure the reverse > channel with a 170mV amplitude before the remote serializers have > probed. > > This change is required for both rdacm20 and rdacm21 camera modules > to be correctly probed when used in combination with the max9286 > deserializer. > > Signed-off-by: Jacopo Mondi > --- > drivers/media/i2c/max9286.c | 74 +++++++++++++++++++++++-------------- > 1 file changed, 47 insertions(+), 27 deletions(-) > > diff --git a/drivers/media/i2c/max9286.c b/drivers/media/i2c/max9286.c > index 163e102199e3..4b59a9e0228a 100644 > --- a/drivers/media/i2c/max9286.c > +++ b/drivers/media/i2c/max9286.c > @@ -163,6 +163,8 @@ struct max9286_priv { > unsigned int mux_channel; > bool mux_open; > > + bool high_threshold; > + > struct v4l2_ctrl_handler ctrls; > struct v4l2_ctrl *pixelrate; > > @@ -436,6 +438,32 @@ static int max9286_check_config_link(struct max9286_priv *priv, > return 0; > } > > +static void max9286_reverse_channel_setup(struct max9286_priv *priv, > + unsigned int chan_amplitude) This looks like you're adding a new function - how about we add this function here, in the first place when you add it in 3/7 > +{ > + /* Reverse channel transmission time: default to 1. */ > + u8 chan_config = MAX9286_REV_TRF(1); > + > + /* > + * Reverse channel setup. > + * > + * - Enable custom reverse channel configuration (through register 0x3f) > + * and set the first pulse length to 35 clock cycles. > + * - Adjust reverse channel amplitude: values > 130 are programmed > + * using the additional +100mV REV_AMP_X boost flag > + */ > + max9286_write(priv, 0x3f, MAX9286_EN_REV_CFG | MAX9286_REV_FLEN(35)); > + > + if (chan_amplitude > 100) { > + /* It is not possible express values (100 < x < 130) */ > + chan_amplitude = chan_amplitude < 130 > + ? 30 : chan_amplitude - 100; > + chan_config |= MAX9286_REV_AMP_X; > + } > + max9286_write(priv, 0x3b, chan_config | MAX9286_REV_AMP(chan_amplitude)); > + usleep_range(2000, 2500); > +} > + > /* ----------------------------------------------------------------------------- > * V4L2 Subdev > */ > @@ -531,10 +559,14 @@ static int max9286_notify_bound(struct v4l2_async_notifier *notifier, > * All enabled sources have probed and enabled their reverse control > * channels: > * > + * - Increase the reverse channel amplitude to compensate for the > + * remote ends high threshold, if not done already > * - Verify all configuration links are properly detected > * - Disable auto-ack as communication on the control channel are now > * stable. > */ > + if (!priv->high_threshold) > + max9286_reverse_channel_setup(priv, 170); is it troublesome to re-set it if it's already set? I guess it's just unnecessary. so that's fine. > max9286_check_config_link(priv, priv->source_mask); > > /* > @@ -906,32 +938,6 @@ static void max9286_v4l2_unregister(struct max9286_priv *priv) > * Probe/Remove > */ > > -static void max9286_reverse_channel_setup(struct max9286_priv *priv, > - unsigned int chan_amplitude) > -{ > - /* Reverse channel transmission time: default to 1. */ > - u8 chan_config = MAX9286_REV_TRF(1); > - > - /* > - * Reverse channel setup. > - * > - * - Enable custom reverse channel configuration (through register 0x3f) > - * and set the first pulse length to 35 clock cycles. > - * - Adjust reverse channel amplitude: values > 130 are programmed > - * using the additional +100mV REV_AMP_X boost flag > - */ > - max9286_write(priv, 0x3f, MAX9286_EN_REV_CFG | MAX9286_REV_FLEN(35)); > - > - if (chan_amplitude > 100) { > - /* It is not possible express values (100 < x < 130) */ > - chan_amplitude = chan_amplitude < 130 > - ? 30 : chan_amplitude - 100; > - chan_config |= MAX9286_REV_AMP_X; > - } > - max9286_write(priv, 0x3b, chan_config | MAX9286_REV_AMP(chan_amplitude)); > - usleep_range(2000, 2500); > -} > - > static int max9286_setup(struct max9286_priv *priv) > { > /* > @@ -967,7 +973,15 @@ static int max9286_setup(struct max9286_priv *priv) > * only. This should be disabled after the mux is initialised. > */ > max9286_configure_i2c(priv, true); > - max9286_reverse_channel_setup(priv, 170); > + > + /* > + * Compensate the remote end high threshold with a larger channel > + * amplitude if necessary. > + */ > + if (priv->high_threshold) > + max9286_reverse_channel_setup(priv, 170); > + else > + max9286_reverse_channel_setup(priv, 100); Hrm... ternery is more concise here, but is it helpful? max9286_reverse_channel_setup(priv, priv->high_threshold ? 170 : 100); The high-threshold could also be parsed in max9286_reverse_channel_setup(), but I like it being passed in. > > /* > * Enable GMSL links, mask unused ones and autodetect link > @@ -1235,6 +1249,12 @@ static int max9286_parse_dt(struct max9286_priv *priv) > } > of_node_put(node); > > + /* > + * Parse 'high_threshold' property to configure the reverse channel > + * amplitude. > + */ > + priv->high_threshold = device_property_present(dev, "high_threshold"); > + Oh, I think I like this, it's a neat way to express what it needs to do from the DT depending on the attached cameras. It's sort of dependant upon the cameras though, I guess making this something that we query from the remote endpoint isn't so easy ...? > priv->route_mask = priv->source_mask; > > return 0; >