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Sun, 04 Oct 2026 08:51:47 -0700 (PDT) Message-ID: <8cf6ec52-fb36-44e7-831c-2bb24214f591@linaro.org> Date: Sun, 4 Oct 2026 17:51:44 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird From: Neil Armstrong Reply-To: Neil Armstrong Subject: Re: [PATCH v5 5/6] dt-bindings: display: Add Synaptics panel support To: Dmitry Baryshkov Cc: Linus Walleij , Krzysztof Kozlowski , Jun Nie , Rob Clark , Dmitry Baryshkov , Abhinav Kumar , Jessica Zhang , Sean Paul , Marijn Suijten , David Airlie , Simona Vetter , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , Rob Herring , Krzysztof Kozlowski , Conor Dooley , linux-arm-msm@vger.kernel.org, dri-devel@lists.freedesktop.org, freedreno@lists.freedesktop.org, linux-kernel@vger.kernel.org, devicetree@vger.kernel.org References: <20260727-sm8650-7-1-bonded-dsi-v5-0-c042266b9eeb@linaro.org> <20260727-sm8650-7-1-bonded-dsi-v5-5-c042266b9eeb@linaro.org> <20260727-spotted-winged-mantis-7aa1ce@quoll> <668e83d0-a017-4f59-bc76-bf6c9a80b5ba@kernel.org> <2lcpzwh7fxecpffnakpnp5lecrm3e6u64ztat7cd75nuxofxa2@clj27bzgjy3r> <4d053234-06d8-4268-b60a-2fccc78da654@linaro.org> Content-Language: en-US, fr Autocrypt: addr=neil.armstrong@linaro.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 10/1/26 02:43, Dmitry Baryshkov wrote: > On Wed, Sep 30, 2026 at 09:18:55PM +0200, Neil Armstrong wrote: >> On 9/30/26 21:04, Dmitry Baryshkov wrote: >>> On Wed, Sep 30, 2026 at 06:43:47PM +0200, Neil Armstrong wrote: >>>> On 9/30/26 09:44, Linus Walleij wrote: >>>>> On Tue, Sep 29, 2026 at 3:35 PM Krzysztof Kozlowski wrote: >>>>> >>>>>> This entire binding seems like stitching two devices together, which >>>>>> might be fine (I don't even remember this stuff... two months old) or >>>>>> might be artificial grouping of separate devices. >>>>> >>>>> I think that's a good point and fair pushback. >>>>> >>>>> Neil and Jun talk about it yesterday at XDC (1:15 into the stream): >>>>> https://www.youtube.com/watch?v=6tNGW8PoSzw >>>>> >>>>> The current binding does not reflect the physical topology of the >>>>> actual device, and the bindings need improvements. I have a feeling >>>>> there is one display controller with two physical panels. >>>> >>>> No there's really 2 controller and 2 separate panels, but they are not >>>> classic panel, they are a pair of panels+lens which are in front of >>>> the eyes which forms a single "image" for the brain, so they are >>>> technically a single display and requires to be hard synchronized. >>> >>> Yes. However this approach makes it impossible to share the code between >>> the double-panel drivers and single-panel drivers. I think, that the >>> panel driver should still reference a single glass+DDIC, while letting >>> the DSI host driver to handle the bifurcation. >> >> Yes, and no, it must really be considered as a "single panel driven by 2 identical controllers", >> and even this is really purely software implementation issue. > > [...] > > >>>> Describing both panels into separate nodes would only be possible >>>> if we described a "VR display complex" nodes linked to both panels >>>> but this would probably be solved by actually describing the "display" >>>> linked to a DDIC controller and is out of subject for this serie, >>>> and can be added later when we properly define things. >>> >>> I like the VR complex idea. In the end, you have two modes which you >>> most likely might want to support: >>> - L+R, having double-width CRTC scanning over a double-width framebuffer >>> - Mx2, having a single-width CRTC and a single-width framebuffer >>> displaying the same picture to both eyes. I can imaging that knowing >>> about L+R might be an explicit opt-in feature of the DRM interface. >>> >> >> This makes no sense to support both modes, and this will never be used, >> and anyway this is purely software implementation. >> >> We're defining bindings here, describing the real reality, not hypothetical >> situation that will never happen. > > Let's ignore software issues. On the hardware side, you have two > distinct DSI panels, each having its own set of controls, own DSI link > and own backlight control. > OK so let's see the problem in another angle, if we had 2 DS links 2 physical controllers, 2 physically distinct panels but forms an unique display. Describing it in separate distincts nodes is wrong since it doesn't reflect that it's an unified display, so either we define : - a "combined-display" bridge defined as: - a separate top node in / like connectors with a graph from the DSI links to each panel - a DSI subnode with 2 panels as subnode, port graph from both dsi to both sub-panels - a "R63455" panel bindings with 2 subpanels as Linus shared in https://lore.kernel.org/all/CAD++jLkyEPY5cFg_pHb71yG52iLwS9tQDpcHu=TTBknQMeFctw@mail.gmail.com/ I think it would be interesting to have the "combined-display", with a connector-like node, which will do all the split-dsi dual-panel logic for us and leave use implementing simple panel drivers. The outline would be: =====><======================================= / { xr-display { compatible = "combined-display"; ports { port@0 { combined_dsi0: endpoint { remote-endpoint = <&dsi0_out>; }; }; port@1 { combined_dsi1: endpoint { remote-endpoint = <&dsi1_out>; }; }; port@2 { combined_panel0: endpoint { remote-endpoint = <&r63455_right_in>; }; }; port@3 { combined_panel1: endpoint { remote-endpoint = <&r63455_left_in>; }; }; }; }; }; &mdss_dsi0 { vdda-supply = <&vreg_l3i_1p2>; status = "okay"; qcom,dual-dsi-mode; qcom,master-dsi; panel_right: panel@0 { compatible = "sharp,ls026b3sa06", "synaptic reset-gpios = <&pm8550_gpios 3 GPIO_ACTIVE_HIGH>>; pos-supply = <&vpos_right>; neg-supply = <&vneg_right>; backlight-supply = <&backlight_right>; vdda-supply = <&vreg_l12b_1p8>; port { r63455_right_in: endpoint { remote-endpoint = <&combined_panel0>; }; }; }; }; &mdss_dsi0_out { remote-endpoint = <&combined_dsi0>; data-lanes = <0 1 2 3>; }; &mdss_dsi1 { vdda-supply = <&vreg_l3i_1p2>; status = "okay"; qcom,dual-dsi-mode; panel_left: panel@0 { compatible = "sharp,ls026b3sa06", "synaptic reset-gpios = <&pm8550_gpios 19 GPIO_ACTIVE_HIGH>>; pos-supply = <&vpos_left>; neg-supply = <&vneg_left>; backlight-supply = <&backlight_left>; vdda-supply = <&vreg_l12b_1p8>; port { r63455_left_in: endpoint { remote-endpoint = <&combined_panel1>; }; }; }; }; &mdss_dsi1_out { remote-endpoint = <&combined_dsi1>; data-lanes = <0 1 2 3>; }; =====><======================================= So this would solve all the similar use-cases. We can even add the "xr-display" compatible with "combined-fallback" plus some properties to define how the panels are physically placed. Neil