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 09359C433EF for ; Thu, 5 May 2022 20:12:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1359685AbiEEUPy (ORCPT ); Thu, 5 May 2022 16:15:54 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35974 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1385753AbiEEUPm (ORCPT ); Thu, 5 May 2022 16:15:42 -0400 Received: from mail-yb1-xb31.google.com (mail-yb1-xb31.google.com [IPv6:2607:f8b0:4864:20::b31]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5378E5FF00 for ; Thu, 5 May 2022 13:12:00 -0700 (PDT) Received: by mail-yb1-xb31.google.com with SMTP id e12so9496329ybc.11 for ; Thu, 05 May 2022 13:12:00 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=Y3/V47f9z10aY8fNVMYn8QvpcDbl57QLdHc+QoKNSM4=; b=XwLN5A6p91UcSNtBV3WitaWWZCXN+PQ1ijSepyAK/JU+qrB0Frq0QEnuNNbDVPXoW9 N+Tyfqqdmzjcsd2brB2ohjsV3pGVMZVK+lcAwija8hL4idjAWJXdMQrzaXoEmY9hixsz 3mtT+CxXdet61uAxerkNaC9g8u8rIITBPYcWZdPJojCrwT28Jn1//PH1HoyUK/96LkFH tCGVOj9XLI477hArTy5vE2JLHV439HAss42zk8IquaCn7vWYnrjzVY0d6MUIEnw9G+I/ /auDdJUncPXPmTSJgX02V6/zGvSFvam41/L7VADvMsLpRu8I01cT6egae7ejS/TCfKkE ji7w== 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=Y3/V47f9z10aY8fNVMYn8QvpcDbl57QLdHc+QoKNSM4=; b=PX9HE5x12tvhiE7ojVtDhgocwYwerEKXliq9p51NlIeEr7pmC00F0BpxgfdhO0eqpl L70q8OyT7rR335MEID1C3N2tgpCbQi5uoC0UqM4QrlhzpgfGQGO3SI970wSeN3k66tzc Zl0DkAFrxTBomUpKTFL2L1zwyXNmLMztGyam0d7jyaOy8HrCC4WSS9k6LMe+YSGiK5ZJ YHHzzmJ36dgF4Br3ubtPWTTWRY2vPYiU/YjOv6FJOBjS/PA949OXj4ylROaDb/rJG0ee e0DJxwyDj1804NHwdO32AKP+VVha4AD2Yg7onA8qKEJL6rIf//0i7ymvArCDPaWh9lBw 9k9w== X-Gm-Message-State: AOAM5321c3HBVtK+HrcgGYMAsnDxpy7cMrlFhiaHQBzvdIvYRhNuN8AA LJk/wWuL3fB4umf3SB6jbTfWzN6NmUQ8J+sl/pfjMg== X-Google-Smtp-Source: ABdhPJwlb98UW3/pGaDYgW02qFbBFTz3qjiSA/ybeqhoTQ7mgT0cFwCIUDSnzBv+M/FkeEgh+eOVojR8YTDJx7Lvpeo= X-Received: by 2002:a25:b1a5:0:b0:648:e230:aef with SMTP id h37-20020a25b1a5000000b00648e2300aefmr24299965ybj.175.1651781519563; Thu, 05 May 2022 13:11:59 -0700 (PDT) MIME-Version: 1.0 References: <20220426114627.1.I2dd93486c6952bd52f2020904de0133970d11b29@changeid> <20220426114627.2.I4ac7f55aa446699f8c200a23c10463256f6f439f@changeid> <4186ab8f-d227-f2c7-ab3f-0729bb915f17@quicinc.com> <01852b37-faf7-c4ab-b159-e525c03d6e54@quicinc.com> In-Reply-To: <01852b37-faf7-c4ab-b159-e525c03d6e54@quicinc.com> From: Dmitry Baryshkov Date: Thu, 5 May 2022 23:11:24 +0300 Message-ID: Subject: Re: [PATCH 2/2] drm/probe-helper: For DP, add 640x480 if all other modes are bad To: Kuogee Hsieh Cc: Abhinav Kumar , Doug Anderson , dri-devel , =?UTF-8?B?VmlsbGUgU3lyasOkbMOk?= , Sankeerth Billakanti , Thomas Zimmermann , David Airlie , linux-arm-msm , LKML , "Aravind Venkateswaran (QUIC)" , Stephen Boyd Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 5 May 2022 at 20:30, Kuogee Hsieh wrote: > > > On 5/5/2022 10:20 AM, Abhinav Kumar wrote: > > Hi Doug > > > > On 5/5/2022 8:44 AM, Doug Anderson wrote: > >> Ville, > >> > >> On Tue, Apr 26, 2022 at 11:47 AM Douglas Anderson > >> wrote: > >>> > >>> As per Displayport spec section 5.2.1.2 ("Video Timing Format") says > >>> that all detachable sinks shall support 640x480 @60Hz as a fail safe > >>> mode. > >>> > >>> A DP compliance test expected us to utilize the above fact when all > >>> modes it presented to the DP source were not achievable. It presented > >>> only modes that would be achievable with more lanes and/or higher > >>> speeds than we had available and expected that when we couldn't do > >>> that then we'd fall back to 640x480 even though it didn't advertise > >>> this size. > >>> > >>> In order to pass the compliance test (and also support any users who > >>> might fall into a similar situation with their display), we need to > >>> add 640x480 into the list of modes. However, we don't want to add > >>> 640x480 all the time. Despite the fact that the DP spec says all sinks > >>> _shall support_ 640x480, they're not guaranteed to support it > >>> _well_. Continuing to read the spec you can see that the display is > >>> not required to really treat 640x480 equal to all the other modes. It > >>> doesn't need to scale or anything--just display the pixels somehow for > >>> failsafe purposes. It should also be noted that it's not hard to find > >>> a display hooked up via DisplayPort that _doesn't_ support 640x480 at > >>> all. The HP ZR30w screen I'm sitting in front of has a native DP port > >>> and doesn't work at 640x480. I also plugged in a tiny 800x480 HDMI > >>> display via a DP to HDMI adapter and that screen definitely doesn't > >>> support 640x480. > >>> > >>> As a compromise solution, let's only add the 640x480 mode if: > >>> * We're on DP. > >>> * All other modes have been pruned. > >>> > >>> This acknowledges that 640x480 might not be the best mode to use but, > >>> since sinks are _supposed_ to support it, we will at least fall back > >>> to it if there's nothing else. > >>> > >>> Note that we _don't_ add higher resolution modes like 1024x768 in this > >>> case. We only add those modes for a failed EDID read where we have no > >>> idea what's going on. In the case where we've pruned all modes then > >>> instead we only want 640x480 which is the only defined "Fail Safe" > >>> resolution. > >>> > >>> This patch originated in response to Kuogee Hsieh's patch [1]. > >>> > >>> [1] > >>> https://lore.kernel.org/r/1650671124-14030-1-git-send-email-quic_khsieh@quicinc.com > >>> > >>> Signed-off-by: Douglas Anderson > >>> --- > >>> > >>> drivers/gpu/drm/drm_probe_helper.c | 26 +++++++++++++++++++++----- > >>> 1 file changed, 21 insertions(+), 5 deletions(-) > >> > >> I think this patch is fairly safe / non-controversial, but someone > >> suggested you might have an opinion on it and another patch I posted > >> recently [1] so I wanted to double-check. Just to be clear: I'm hoping > >> to land _both_ this patch and [1]. If you don't have an opinion, > >> that's OK too. > >> > >> Abhinav: I think maybe you're happy with this now? Would you be > >> willing to give a Reviewed-by? > > > > Yes, I have no concerns with this approach from DP spec standpoint and > > in addition, kuogee has tested this out and this does help us to pass > > the tests. > > > > Although, I might be missing some historical context on why this is > > not already done. > > > > But apart from that, LGTM. Hence, > > > > Reviewed-by: Abhinav Kumar > > Tested-by: Kuogee Hsieh This line got wrong quotation level, so it will not be noticed by patchwork (and can be easily missed by other people too). Please resend. > >> > >> [1] > >> https://lore.kernel.org/r/20220426132121.RFC.1.I31ec454f8d4ffce51a7708a8092f8a6f9c929092@changeid > >> > >> -Doug -- With best wishes Dmitry