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 9A05BC41513 for ; Thu, 3 Aug 2023 14:55:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235211AbjHCOzs (ORCPT ); Thu, 3 Aug 2023 10:55:48 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34286 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231874AbjHCOzr (ORCPT ); Thu, 3 Aug 2023 10:55:47 -0400 Received: from mail-ej1-x62c.google.com (mail-ej1-x62c.google.com [IPv6:2a00:1450:4864:20::62c]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 91019EA for ; Thu, 3 Aug 2023 07:55:45 -0700 (PDT) Received: by mail-ej1-x62c.google.com with SMTP id a640c23a62f3a-99bd67facffso29114966b.0 for ; Thu, 03 Aug 2023 07:55:45 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ffwll.ch; s=google; t=1691074544; x=1691679344; h=in-reply-to:content-disposition:mime-version:references :mail-followup-to:message-id:subject:cc:to:from:date:from:to:cc :subject:date:message-id:reply-to; bh=0Mlirwl0bkHM2riavE8GsJIkOTqsTSTy4yuuyAhKnAo=; b=dXcMVKZ263XM80AEP96Op45kPHn2B0z7632FrqP2dpNskATpF+7o/TLVLGiZ9ATXYY OSXR6ZsnU8GpH6OYseVc7B4N/q9CQbm1By39X7X5z7a7wXau02SsGlaE3PBl4GFscQK6 edH0MGrDaYySh3+zRj/OHNfHuICnMBm+1+Usc= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1691074544; x=1691679344; h=in-reply-to:content-disposition:mime-version:references :mail-followup-to:message-id:subject:cc:to:from:date :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=0Mlirwl0bkHM2riavE8GsJIkOTqsTSTy4yuuyAhKnAo=; b=UzMlM6CuGp/hi2aKg/xmBMwTbrz+TAJRMJxMHO4dBEXDiiLkc41hcmg2DdtgVr8cdU odSY9nDL5J7ju3lXd5G6Zxh5eW4JXsE0kGdzZqokKFnpILVs/Q01K7dUCSueAL2y7uez 5yY3VQLZ3mfPj3u4+ofBCvaD3l+RSpS044IIZzT1fylnCltcbICh8dMdSe0exyGeFT8b rSVeEIeGBkXuiLeAmX4IAmfuhWt509IkQpYGgORrPvGNPcvHylSpRA508l9AxO4ONLVc XOlW5FWgTbX5Ashl0T7POOq4oFtlIB4+1ffkC1FBVG0a/AytrH/rCJO40TNV+EsA++mr uW6A== X-Gm-Message-State: ABy/qLZTTrOYxG6RvT2InEhNKHrzO9anR4pWdawmv7p3gImzwumqYqjA EnX/ikq/HySmtP7SH1fAtcTlXA== X-Google-Smtp-Source: APBJJlHmkF1RcJMqyHh/L6fwZfWL4t0iAsi7uo+0RzF5aZvjdZDTsxLeQhB63n9BKAKqMFbVtvvGUw== X-Received: by 2002:a17:906:10da:b0:987:115d:ba06 with SMTP id v26-20020a17090610da00b00987115dba06mr12074936ejv.4.1691074543899; Thu, 03 Aug 2023 07:55:43 -0700 (PDT) Received: from phenom.ffwll.local ([2a02:168:57f4:0:efd0:b9e5:5ae6:c2fa]) by smtp.gmail.com with ESMTPSA id f15-20020a1709067f8f00b00985ed2f1584sm10620124ejr.187.2023.08.03.07.55.42 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 03 Aug 2023 07:55:43 -0700 (PDT) Date: Thu, 3 Aug 2023 16:55:40 +0200 From: Daniel Vetter To: Maxime Ripard Cc: Daniel Vetter , Neil Armstrong , Michael Riesch , Sam Ravnborg , Sebastian Reichel , Gerald Loacker , David Airlie , Miquel Raynal , Conor Dooley , Krzysztof Kozlowski , Rob Herring , devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org Subject: Re: [PATCH 0/4] drm/panel: sitronix-st7789v: add support for partial mode Message-ID: Mail-Followup-To: Maxime Ripard , Neil Armstrong , Michael Riesch , Sam Ravnborg , Sebastian Reichel , Gerald Loacker , David Airlie , Miquel Raynal , Conor Dooley , Krzysztof Kozlowski , Rob Herring , devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org References: <20230718-feature-lcd-panel-v1-0-e9a85d5374fd@wolfvision.net> <292c3e7d-82ea-2631-bd4b-ef747f56287c@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Operating-System: Linux phenom 6.3.0-2-amd64 Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org On Thu, Aug 03, 2023 at 01:43:08PM +0200, Maxime Ripard wrote: > On Thu, Aug 03, 2023 at 12:26:03PM +0200, Daniel Vetter wrote: > > On Thu, 3 Aug 2023 at 11:22, Maxime Ripard wrote: > > > > > > On Thu, Aug 03, 2023 at 10:51:57AM +0200, Daniel Vetter wrote: > > > > On Thu, Aug 03, 2023 at 10:48:57AM +0200, Maxime Ripard wrote: > > > > > On Thu, Aug 03, 2023 at 10:11:22AM +0200, Neil Armstrong wrote: > > > > > > Hi, > > > > > > > > > > > > On 18/07/2023 17:31, Michael Riesch wrote: > > > > > > > Hi all, > > > > > > > > > > > > > > This series adds support for the partial display mode to the Sitronix > > > > > > > ST7789V panel driver. This is useful for panels that are partially > > > > > > > occluded by design, such as the Jasonic JT240MHQS-HWT-EK-E3. Support > > > > > > > for this particular panel is added as well. > > > > > > > > > > > > > > Note: This series is already based on > > > > > > > https://lore.kernel.org/lkml/20230714013756.1546769-1-sre@kernel.org/ > > > > > > > > > > > > I understand Maxime's arguments, but by looking closely at the code, > > > > > > this doesn't look like an hack at all and uses capabilities of the > > > > > > panel controller to expose a smaller area without depending on any > > > > > > changes or hacks on the display controller side which is coherent. > > > > > > > > > > > > Following's Daniel's summary we cannot compare it to TV overscan > > > > > > because overscan is only on *some* displays, we can still get 100% > > > > > > of the picture from the signal. > > > > > > > > > > Still disagree on the fact that it only affects some display. But it's > > > > > not really relevant for that series. > > > > > > > > See my 2nd point, from a quick grep aside from i915 hdmi support, no one > > > > else sets all the required hdmi infoframes correctly. Which means on a > > > > compliant hdmi tv, you _should_ get overscan. That's how that stuff is > > > > speced. > > > > > > > > Iirc you need to at least set both the VIC and the content type, maybe > > > > even more stuff. > > > > > > > > Unless all that stuff is set I'd say it's a kms driver bug if you get > > > > overscan on a hdmi TV. > > > > > > I have no doubt that i915 works there. The source of my disagreement is > > > that if all drivers but one don't do that, then userspace will have to > > > care. You kind of said it yourself, i915 is kind of the exception there. > > > > > > The exception can be (and I'm sure it is) right, but still, it deviates > > > from the norm. > > > > The right fix for these is sending the right infoframes, _not_ trying > > to fiddle with overscan margins. Only the kernel can make sure the > > right infoframes are sent out. If you try to paper over this in > > userspace, you'll make the situation worse, not better (because > > fiddling with overscan means you get scaling, and so rescaling > > artifacts, and for hard contrasts along pixel lines that'll look like > > crap). > > > > So yeah this is a case of "most upstream hdmi drivers are broken". > > Please don't try to fix kernel bugs in userspace. > > ACK. > > > > > > I think I'll still like to have something clarified before we merge it: > > > > > if userspace forces a mode, does it contain the margins or not? I don't > > > > > have an opinion there, I just think it should be documented. > > > > > > > > The mode comes with the margins, so if userspace does something really > > > > funny then either it gets garbage (as in, part of it's crtc area isn't > > > > visible, or maybe black bars on the screen), or the driver rejects it > > > > (which I think is the case for panels, they only take their mode and > > > > nothing else). > > > > > > Panels can usually be quite flexible when it comes to the timings they > > > accept, and we could actually use that to our advantage, but even if we > > > assume that they have a single mode, I don't think we have anything that > > > enforces that, either at the framework or documentation levels? > > > > Maybe more bugs? We've been slowly filling out all kinds of atomic kms > > validation bugs in core/helper code because as a rule of thumb, > > drivers get it wrong. Developers test until things work, then call it > > good enough, and very few driver teams make a serious effort in trying > > to really validate all invalid input. Because doing that is an > > enormous amount of work. > > > > I think for clear-cut cases like drm_panel the fix is to just put more > > stricter validation into shared code (and then if we break something, > > figure out how we can be sufficiently lenient again). > > Panels are kind of weird, since they essentially don't exist at all in > the framework so it's difficult to make it handle them or their state. > > It's typically handled by encoders directly, so each and every driver > would need to make that check, and from a quick grep, none of them are > (for the reasons you said). I think the panel bridge driver infra is the right spot to put this, and then push drivers a bit more towards using that. Because yeah if they hand-roll the panel integration, they'll probably miss a lot of these details :-/ -Sima > > Just like for HDMI, even though we can commit to changing those facts, > it won't happen overnight, so to circle back to that series, I'd like a > comment in the driver when the partial mode is enabled that if userspace > ever pushes a mode different from the expected one, we'll add the margins. > > That way, if and when we come back to it, we'll know what the original > intent and semantics were. > > Maxime -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch