From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from perceval.ideasonboard.com (perceval.ideasonboard.com [213.167.242.64]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5EB7F31F9BA; Mon, 6 Jul 2026 16:02:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=213.167.242.64 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783353772; cv=none; b=JCX3vafj9z0jPqyInZE1d+beextMdpPV+a2tnmzV5KIsYtzyZTGFQSCd4eZ5ldOaKzZYIeqs7x4xOiOicpIftDLrXjrpuluW3oD+8xz9OPYBxDoJEKEGEnhecjFy922wnRCO4afMxbijeeO5PawfhpVxCfZRnQeMY5m77ZqzSQE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783353772; c=relaxed/simple; bh=i8nf4O2WsIEE/n0S6fpBF1M5knrAG/jCBg9Deoxto/g=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=mphzjaYMq0QzhsIJnyWTyV8E9QT1+gqUZPU5bwRHWCIRAZBp3GtAbczOA5hPlcuJJNIE1/jA+Ye5DnZXPeS2hhNcB1FhmS5ea4HWLN4/5L+cUoSDt0vFN2yCSvX4Kn3mrssmwxCZOyw0QhCvIbJcwIZNjJKUFkFvukYaN0T6Exs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=ideasonboard.com; spf=pass smtp.mailfrom=ideasonboard.com; dkim=pass (1024-bit key) header.d=ideasonboard.com header.i=@ideasonboard.com header.b=gqvl818r; arc=none smtp.client-ip=213.167.242.64 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=ideasonboard.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=ideasonboard.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=ideasonboard.com header.i=@ideasonboard.com header.b="gqvl818r" Received: from killaraus.ideasonboard.com (2001-14ba-70f3-e800--a06.rev.dnainternet.fi [IPv6:2001:14ba:70f3:e800::a06]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id 87983838; Mon, 6 Jul 2026 18:01:56 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1783353716; bh=i8nf4O2WsIEE/n0S6fpBF1M5knrAG/jCBg9Deoxto/g=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=gqvl818rEpx0lnDUiRHq56bBrBsKS5t0JACNhhFJMKIaFgOPv9L7D8f2hhAD5DqgO pO3LPdjvI5DXRHsXH3yigetnhZPdZQprn8TzXrLhLwLouugdFVDbJeX3d//aAUAEiq Enwsb7eaJcpspMTh6pMmWMJHFYlF7WKmJMqHRh28= Date: Mon, 6 Jul 2026 19:02:43 +0300 From: Laurent Pinchart To: Maxime Ripard Cc: dri-devel@lists.freedesktop.org, devicetree@vger.kernel.org, Thuan Nguyen , Maarten Lankhorst , Thomas Zimmermann , Rob Herring , Krzysztof Kozlowski , Conor Dooley , Geert Uytterhoeven , Magnus Damm , Andrzej Hajda , Neil Armstrong , Robert Foss , Jonas Karlman , Jernej Skrabec , Luca Ceresoli , linux-renesas-soc@vger.kernel.org Subject: Re: [PATCH 1/4] dt-bindings: display: vga-connector: Allow hardcoding EDID Message-ID: <20260706160243.GB106045@killaraus.ideasonboard.com> References: <20260705213542.28987-1-laurent.pinchart+renesas@ideasonboard.com> <20260705213542.28987-2-laurent.pinchart+renesas@ideasonboard.com> <20260706-capable-beaver-of-excellence-a3cf10@houat> <20260706094522.GA42740@killaraus.ideasonboard.com> <20260706-fancy-perch-of-satiation-0c220e@houat> Precedence: bulk X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20260706-fancy-perch-of-satiation-0c220e@houat> On Mon, Jul 06, 2026 at 05:40:30PM +0200, Maxime Ripard wrote: > On Mon, Jul 06, 2026 at 12:45:22PM +0300, Laurent Pinchart wrote: > > On Mon, Jul 06, 2026 at 10:52:32AM +0200, Maxime Ripard wrote: > > > On Mon, Jul 06, 2026 at 12:35:39AM +0300, Laurent Pinchart wrote: > > > > Since DDC version 2, introduced in 1996, VGA monitors have exposed EDID > > > > data over an I2C bus. The bus is also used to detect the presence of a > > > > connected monitor by trying to read the EDID data. > > > > > > > > Some devices where the VGA display is integrated in the device and > > > > always connected do not connect the DDC pins. Some development boards, > > > > such as the Renesas M3N Salvator-XS, also do not connect the DDC pins. > > > > > > > > To support those, add the ability to provide hardcoded EDID data in the > > > > device tree. This is mutually exclusive with specifying a DDC bus, and > > > > can only be done when the VGA display is guaranteed to be always > > > > connected. > > > > > > > > Signed-off-by: Laurent Pinchart > > > > > > This feels redundant with the EDID firmware loading mechanism we have in > > > KMS already. It should at least be mentioned why we would need to set it > > > in the device tree at all. > > > > Very good question. > > > > I assume you're talking about CONFIG_DRM_LOAD_EDID_FIRMWARE, as the > > debugfs override_edid feature isn't meant for production. If there are > > other relevant mechanisms I'm not aware of, please let me know. > > No, that's indeed what I meant. > > > In the use case at hand, the VGA display is an integral part of the > > device, the same way an LVDS or DSI panel would be. Using > > CONFIG_DRM_LOAD_EDID_FIRMWARE, the manufacturer would need to set the > > drm.edid_firmware command line parameter, and provide EDID as a file in > > /lib/firmware/ (possibly in an initramfs). Beside the complexity, and > > the fact it won't be very friendly to people who run a different > > userspace on the device, I think EDID counts in this case as system > > description, the same way we support specifying panel timings in device > > tree. > > It's *some* hardware description, but you have no idea whether it's > actually the hardware you're running from. What would be in that EDID > anyway? It would be the EDID corresponding to the connected display :-) I see it as identical to how a user of the simple panel driver is responsible for listing the timings corresponding to the hardware in the device tree. > There's another alternative we've used several times already, in > simple-bridge for example: just register any VESA mode up to a given > resolution: > https://elixir.bootlin.com/linux/v7.1.2/source/drivers/gpu/drm/bridge/simple-bridge.c#L66 I don't see how that would help. The goal is to provide the kernel with the data corresponding to the display integrated in the device. > I guess it's what you would do with that EDID anyway? -- Regards, Laurent Pinchart