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Wed, 14 Oct 2026 15:36:37 +0000 Date: Wed, 14 Oct 2026 10:36:25 -0500 From: Frank Li To: Leonardo Costa Cc: Laurent Pinchart , Francesco Dolcini , Andrzej Hajda , Neil Armstrong , Robert Foss , Jonas Karlman , Jernej Skrabec , Luca Ceresoli , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , Rob Herring , Krzysztof Kozlowski , Conor Dooley , Frank Li , Sascha Hauer , Pengutronix Kernel Team , Fabio Estevam , dri-devel@lists.freedesktop.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, imx@lists.linux.dev, linux-arm-kernel@lists.infradead.org, Leonardo Costa Subject: Re: [PATCH 0/3] Add VGA support for Apalis iMX6 Message-ID: References: <20261012-v1-apalis-imx6-enable-vga-v1-0-8905d8746504@toradex.com> <20261012164054.GA56180@killaraus.ideasonboard.com> <20261013090631.GA33628@francesco-nb> <20261013111158.GG56180@killaraus.ideasonboard.com> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-ClientProxiedBy: DM6PR07CA0091.namprd07.prod.outlook.com (2603:10b6:5:337::24) To GV2PR04MB11799.eurprd04.prod.outlook.com (2603:10a6:150:2cf::9) Precedence: bulk X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: GV2PR04MB11799:EE_|AM0PR04MB6932:EE_ X-MS-Office365-Filtering-Correlation-Id: 99fcc377-c82d-411e-20b1-08df2a08ef2e X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|23010399003|366016|376014|7416014|19092799006|56012099006|11063799006|4143699003|261009223027099003|22082099003|10067099003|18002099003|6133799003|3023799007; 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For the bridge to work properly, this series also > > > > > changes the following in the dt-bindings and simple-bridge driver: > > > > > > > > > > - dt-bindings: Add a new compatible for the bridge in the simple-bridge > > > > > binding. This is necessary because the existing dumb-vga-dac compatible > > > > > doesn't describe a data-enable signal polarity. > > > > > > > > > > - simple-bridge: Add the VGA bridge match-table entry and timings > > > > > struct, setting the DRM_BUS_FLAG_DE_LOW flag for the bridge. > > > > > > > > Is there schematics available anywhere ? That would help reviewing the > > > > series ? > > > > > > This circuit is on the SoM, and the SoM schematics are > > > confidential and not generally available. > > > > > > I tried to extract as ascii art the relevant circuit, hope it helps > > > > Thank you, it makes things clearer. > > > > The circuit seems fairly generic. Wouldn't it be better to add an > > optional property ot the dumb-vga-dac instead of a new compatible string > > specific to Apalis ? > > See the diff below, this was the initial idea we had when working on > this. On one hand, at least to me it seems like something that other > bridges could use, and a new property seems reasonable. On the other, > since we don't know exactly how much configuration is expected from a > bridge in the simple-bridge driver, we weren't sure if this would be > accepted, and went with the simpler solution of creating a new binding > for our bridge, which also seemed less intrusive. Look like add data-enable-active make sense at this case. You can try it. Frank > > What are your thoughts about a change like this? > > diff --git a/drivers/gpu/drm/bridge/simple-bridge.c b/drivers/gpu/drm/bridge/simple-bridge.c > index 3fba7002322e..41b00a44983a 100644 > --- a/drivers/gpu/drm/bridge/simple-bridge.c > +++ b/drivers/gpu/drm/bridge/simple-bridge.c > @@ -171,6 +171,7 @@ static int simple_bridge_probe(struct platform_device *pdev) > { > struct simple_bridge *sbridge; > struct device_node *remote; > + u32 de; > > sbridge = devm_drm_bridge_alloc(&pdev->dev, struct simple_bridge, > bridge, &simple_bridge_bridge_funcs); > @@ -212,6 +213,19 @@ static int simple_bridge_probe(struct platform_device *pdev) > sbridge->bridge.of_node = pdev->dev.of_node; > sbridge->bridge.timings = sbridge->info->timings; > > + if (!sbridge->bridge.timings && > + !of_property_read_u32(pdev->dev.of_node, "data-enable-active", &de)) { > + struct drm_bridge_timings *timings; > + > + timings = devm_kzalloc(&pdev->dev, sizeof(*timings), GFP_KERNEL); > + if (!timings) > + return -ENOMEM; > + > + timings->input_bus_flags = de ? DRM_BUS_FLAG_DE_HIGH : > + DRM_BUS_FLAG_DE_LOW; > + sbridge->bridge.timings = timings; > + } > + > return devm_drm_bridge_add(&pdev->dev, &sbridge->bridge); > } >