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([2a01:e0a:982:cbb0:8656:583:d034:d966]) by smtp.gmail.com with ESMTPSA id p16-20020a5d68d0000000b003140f47224csm21286033wrw.15.2023.08.03.02.30.53 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 03 Aug 2023 02:30:53 -0700 (PDT) Message-ID: <9f0670a7-6ef6-7823-19c2-de10683f303f@linaro.org> Date: Thu, 3 Aug 2023 11:30:52 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 From: Neil Armstrong Reply-To: neil.armstrong@linaro.org Subject: Re: [PATCH 0/4] drm/panel: sitronix-st7789v: add support for partial mode Content-Language: en-US To: Maxime Ripard , 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> Organization: Linaro Developer Services In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org On 03/08/2023 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. HDMI spec is hidden behind a paywall, HDMI testing is a mess, HDMI real implementation on TVs and Displays is mostly broken, and HDMI certification devices are too expensive... this is mainly why only i915 handles it correctly. > >>> 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? Yep, this is why we would need a better atomic based panel API that would permit us handling dynamic timings for panel and get out of the single-mode for modern panels. Neil > > Maxime