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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9B4F1C43219 for ; Wed, 23 Feb 2022 18:20:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S243808AbiBWSVD (ORCPT ); Wed, 23 Feb 2022 13:21:03 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51446 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S243804AbiBWSVC (ORCPT ); Wed, 23 Feb 2022 13:21:02 -0500 Received: from mail-ed1-x529.google.com (mail-ed1-x529.google.com [IPv6:2a00:1450:4864:20::529]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 62F6749FBA for ; Wed, 23 Feb 2022 10:20:34 -0800 (PST) Received: by mail-ed1-x529.google.com with SMTP id s14so28183879edw.0 for ; Wed, 23 Feb 2022 10:20:34 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=kc817LydO28fR6UkAPJN+rJA2Gepj0IpXCsI544eHP0=; b=hXkbGMYnWmwgIGl12e3NPzs5q+2Lgx8L+R2+dw2D7uuQK3jF07CqtynQW9kqCY8jiz 9ax3T/B/9vUsDEPKt0lz6WV67/I1ZdJj5Dqo93BAQomcLcnjHrOsI0C8BV8ixjHWuEEt a3lHWmQ9yRRUixbMzbtt4mgK8WEH4rm0XgbxI= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=kc817LydO28fR6UkAPJN+rJA2Gepj0IpXCsI544eHP0=; b=crfpNb4bi9HdsBPmd4yclAWDgTWwycytAiiH9Xees60iYBhTf04nXPTW5o4DHISjV8 9AAMwNtmslq6z92m6CmftXMuSBdWZrnx+Ube0M3t7lUanolIkhGVkKxFIbIK5eDKuj2l 3H+7NqOhO6xOakhLNxwsGdoqfHmf077CmiMGN3tLIsU75//TOFMmyo89SxoFLESxYTuJ uS6BG5Zdy9NPxGnUbRprX0Ut5gP1vti+qIPU7ueqStOZ2cZYBQRqf0LTho8BKaoAO8Lo +25phTxUCZDByheZR6Hf2p58lkxi7/yJFbU5GpUkNVu5a2KgrTzvvBBMM+gamm9ok2y5 NxHA== X-Gm-Message-State: AOAM530dhmMOqhZsFKwd5TLCVWF2OA4U5A7cWQ/lCZHCjBWqTkNaWdp7 tvy/mWcf0NbybD42+B3BPggl1WfDj4B/WfMfHs0= X-Google-Smtp-Source: ABdhPJw6LBjR28DvRoNd7H6DYWmRBg85dEtHgwftbAIPxEiACDmvuj/4Y3fQoDfQlyZPChs/jEgrLg== X-Received: by 2002:a05:6402:2553:b0:412:8684:bd34 with SMTP id l19-20020a056402255300b004128684bd34mr691161edb.436.1645640432665; Wed, 23 Feb 2022 10:20:32 -0800 (PST) Received: from mail-wr1-f46.google.com (mail-wr1-f46.google.com. [209.85.221.46]) by smtp.gmail.com with ESMTPSA id q8sm220596edt.78.2022.02.23.10.20.31 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 23 Feb 2022 10:20:31 -0800 (PST) Received: by mail-wr1-f46.google.com with SMTP id s13so12506062wrb.6 for ; Wed, 23 Feb 2022 10:20:31 -0800 (PST) X-Received: by 2002:a5d:5112:0:b0:1ed:c1da:4ad2 with SMTP id s18-20020a5d5112000000b001edc1da4ad2mr660312wrt.342.1645640431088; Wed, 23 Feb 2022 10:20:31 -0800 (PST) MIME-Version: 1.0 References: <20210322030128.2283-1-laurent.pinchart+renesas@ideasonboard.com> <20210322030128.2283-11-laurent.pinchart+renesas@ideasonboard.com> <164563949999.4066078.2399611738908533224@Monstersaurus> In-Reply-To: <164563949999.4066078.2399611738908533224@Monstersaurus> From: Doug Anderson Date: Wed, 23 Feb 2022 10:20:18 -0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [RFC PATCH 10/11] drm/bridge: ti-sn65dsi86: Support DisplayPort (non-eDP) mode To: Kieran Bingham Cc: Laurent Pinchart , Jernej Skrabec , Jonas Karlman , Neil Armstrong , dri-devel , Stephen Boyd , Linux-Renesas , Andrzej Hajda Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-renesas-soc@vger.kernel.org Hi, On Wed, Feb 23, 2022 at 10:05 AM Kieran Bingham wrote: > > > > > + /* For DisplayPort, disable scrambling mode. */ > > > > + if (pdata->bridge.type == DRM_MODE_CONNECTOR_DisplayPort) > > > > + regmap_update_bits(pdata->regmap, SN_TRAINING_SETTING_REG, > > > > + SCRAMBLE_DISABLE, SCRAMBLE_DISABLE); > > > > > > I'm assuming that this is the important part of your patch? Would be > > > sorta nice to include the "why" in your comment. Why do you want to > > > disable scrambling mode for DP but not for eDP? Maybe you care about > > > compatibility but not EMI if you're hooking up to random DP things? > > > > I'll investigate and include proper documentation in v2 (or drop the > > change altogether if it's not required). > > And indeed, this part is important. If I drop this hunk - then I get no > display output. > > I'm afraid I don't (yet) know the reasons 'why' to extend the comment, > beyond "Scrambling is not supported for DP". > > If anyone already does, please feel free to provide the text, and I'll > include it in the next revision, or I'll try to do some more digging > into this part. I don't know _tons_ about it, but I later learned that the "alternate" scrambler is used for eDP and the normal scrambler is used for DP. I don't have any background about why they are different other than what looks to be intentionally making the two things incompatible. ...so I guess that would make it pretty clear why you can't use the alternate scrambler for DP. I haven't personally done the research to know if you can be officially DP compliant with the scrambler disabled. I also don't know why the ti-sn65dsi86 makes it so difficult to switch to the standard scrambler or if it works at all... ;-) -Doug 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 Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id D3332C4332F for ; Wed, 23 Feb 2022 18:20:36 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 09E1810E192; Wed, 23 Feb 2022 18:20:36 +0000 (UTC) Received: from mail-ed1-x529.google.com (mail-ed1-x529.google.com [IPv6:2a00:1450:4864:20::529]) by gabe.freedesktop.org (Postfix) with ESMTPS id D34A710E192 for ; Wed, 23 Feb 2022 18:20:34 +0000 (UTC) Received: by mail-ed1-x529.google.com with SMTP id q17so45813396edd.4 for ; Wed, 23 Feb 2022 10:20:34 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=kc817LydO28fR6UkAPJN+rJA2Gepj0IpXCsI544eHP0=; b=hXkbGMYnWmwgIGl12e3NPzs5q+2Lgx8L+R2+dw2D7uuQK3jF07CqtynQW9kqCY8jiz 9ax3T/B/9vUsDEPKt0lz6WV67/I1ZdJj5Dqo93BAQomcLcnjHrOsI0C8BV8ixjHWuEEt a3lHWmQ9yRRUixbMzbtt4mgK8WEH4rm0XgbxI= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=kc817LydO28fR6UkAPJN+rJA2Gepj0IpXCsI544eHP0=; b=37F5exJLwfFqU8JTWvULRR+bc1qupKkMm/aW6iH3bvyHmi3rB7B/mR35IgjbLFFYm1 cXGtX2r+udGJ3gG8JoVXN2DJ6J0gDuoB2MBFB8prSceiLVF8mvFLoNJzuwxiRuHe+pe4 2JHcaqWfZPLbufSBuGLuHZ27O8z3do9w1iBnFFeS1LIMQOK9yn8Ngu+0zZHCK7JSyPIH 4/FhmH9vkZ85FRlrLlZfq9eTEp3EEl/2zUwoaQYDYWgcoyGydu22/y8goIjG5rBRzUL4 4dqKg+/yVCRTZo/kbMD+4jQdZLHm7ZdTpoZgilN893Qj16NTcG8OsiANDFkbsCHWUH+V Q/2g== X-Gm-Message-State: AOAM531cv/7r8rj0xkZ4FFJlWYqLK0iNK1VQ5XX52YX19Y5ugUpCveUJ pCbk91u1zkcj7V9IGvzBL/DULBjlcAOXL1TAfP8= X-Google-Smtp-Source: ABdhPJy7hb1aUHPvj0gotNR/RMcr84lFhi4wJIaGjhHng/lupGxzUyPJNK8JgDe5w77WxGB0fydLMw== X-Received: by 2002:a05:6402:845:b0:412:ad14:863e with SMTP id b5-20020a056402084500b00412ad14863emr695101edz.380.1645640433045; Wed, 23 Feb 2022 10:20:33 -0800 (PST) Received: from mail-wr1-f46.google.com (mail-wr1-f46.google.com. [209.85.221.46]) by smtp.gmail.com with ESMTPSA id 1sm164430ejm.173.2022.02.23.10.20.31 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 23 Feb 2022 10:20:32 -0800 (PST) Received: by mail-wr1-f46.google.com with SMTP id u1so41009432wrg.11 for ; Wed, 23 Feb 2022 10:20:31 -0800 (PST) X-Received: by 2002:a5d:5112:0:b0:1ed:c1da:4ad2 with SMTP id s18-20020a5d5112000000b001edc1da4ad2mr660312wrt.342.1645640431088; Wed, 23 Feb 2022 10:20:31 -0800 (PST) MIME-Version: 1.0 References: <20210322030128.2283-1-laurent.pinchart+renesas@ideasonboard.com> <20210322030128.2283-11-laurent.pinchart+renesas@ideasonboard.com> <164563949999.4066078.2399611738908533224@Monstersaurus> In-Reply-To: <164563949999.4066078.2399611738908533224@Monstersaurus> From: Doug Anderson Date: Wed, 23 Feb 2022 10:20:18 -0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [RFC PATCH 10/11] drm/bridge: ti-sn65dsi86: Support DisplayPort (non-eDP) mode To: Kieran Bingham Content-Type: text/plain; charset="UTF-8" X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Jernej Skrabec , Neil Armstrong , Jonas Karlman , dri-devel , Stephen Boyd , Linux-Renesas , Andrzej Hajda , Laurent Pinchart Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" Hi, On Wed, Feb 23, 2022 at 10:05 AM Kieran Bingham wrote: > > > > > + /* For DisplayPort, disable scrambling mode. */ > > > > + if (pdata->bridge.type == DRM_MODE_CONNECTOR_DisplayPort) > > > > + regmap_update_bits(pdata->regmap, SN_TRAINING_SETTING_REG, > > > > + SCRAMBLE_DISABLE, SCRAMBLE_DISABLE); > > > > > > I'm assuming that this is the important part of your patch? Would be > > > sorta nice to include the "why" in your comment. Why do you want to > > > disable scrambling mode for DP but not for eDP? Maybe you care about > > > compatibility but not EMI if you're hooking up to random DP things? > > > > I'll investigate and include proper documentation in v2 (or drop the > > change altogether if it's not required). > > And indeed, this part is important. If I drop this hunk - then I get no > display output. > > I'm afraid I don't (yet) know the reasons 'why' to extend the comment, > beyond "Scrambling is not supported for DP". > > If anyone already does, please feel free to provide the text, and I'll > include it in the next revision, or I'll try to do some more digging > into this part. I don't know _tons_ about it, but I later learned that the "alternate" scrambler is used for eDP and the normal scrambler is used for DP. I don't have any background about why they are different other than what looks to be intentionally making the two things incompatible. ...so I guess that would make it pretty clear why you can't use the alternate scrambler for DP. I haven't personally done the research to know if you can be officially DP compliant with the scrambler disabled. I also don't know why the ti-sn65dsi86 makes it so difficult to switch to the standard scrambler or if it works at all... ;-) -Doug