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 134E0175A6C; Fri, 17 Jul 2026 12:25:33 +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=1784291135; cv=none; b=g7TqRjTiWLH9akEKXqKUxeBpu6ke2Y8cYMMSyngp+c9APwpdFZG+SNMwxrFCvXcz+PrKOueV6g2SE8GiIR/mEGPI48EoRXjGmIZ9x8YQAvWa7OyiMpuOQT9NNTTJo6g8lvUtJNM8LSAojDW1Ae8MduK45z4I8iOsfYXSO1oDblY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784291135; c=relaxed/simple; bh=LIrveOCfC/Nm2xJTklxOIDfpSLD9jwkNtd1XzE9uHnI=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=cHYDL3Ga7gnIoA//0OXu/qPSiR1ylxr7HQ38DQ+ytx43QyvCQZcROpV1z4yQlEv20RprsHY7aG9YOk+WSxwzjXvRaD2aMNTJ9Al/zqhwrmYkHdtErT2H7eiXlUf23r1aVSYh/O+1sang2IE1rZaAHq4VRAfqKg9obfthTRpEGAw= 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=fUUzWve9; 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="fUUzWve9" 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 299B5192C; Fri, 17 Jul 2026 14:24:35 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1784291075; bh=LIrveOCfC/Nm2xJTklxOIDfpSLD9jwkNtd1XzE9uHnI=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=fUUzWve9M6ijhuqHco2oiiamtGr16UN66GYsD4wsoE6ZUuICZGnrrOsuY5ORgwwrn 1/LN6VAO2Z8g2+R8JNX5RgzffNCi4svhKJLQyW9nJOlG8OIM3MKFfqCxsMpvbdVbiH +XUx40XMcM8J65RHuLMDh3hZPw6AdyvsXqlvVmcE= Date: Fri, 17 Jul 2026 15:25:30 +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: <20260717122530.GA1955120@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> <20260706160243.GB106045@killaraus.ideasonboard.com> <20260707-meaty-chocolate-lemming-fa9ead@houat> <20260707080143.GA211515@killaraus.ideasonboard.com> 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: <20260707080143.GA211515@killaraus.ideasonboard.com> Hi Maxime, On Tue, Jul 07, 2026 at 11:01:43AM +0300, Laurent Pinchart wrote: > On Tue, Jul 07, 2026 at 09:46:52AM +0200, Maxime Ripard wrote: > > On Mon, Jul 06, 2026 at 07:02:43PM +0300, Laurent Pinchart wrote: > > > 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. > > > > What's the expected user-experience for someone with that board > > unplugging a display and plugging another then? Update the device tree, > > rebuild it, rebuild the firmware and / or resign it and reboot? > > The whole point is that they can't easily unplug the display. This patch > series is meant to support devices where the display is an integral part > of the device. The user experience is expected to be the same as for a > user who will take a phone, remove the display panel, and plug a > different one. It's certainly possible, and they would have to update > the DT indeed. > > > That doesn't sound very practical, and even impossible in some cases. > > > > > > 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. > > > > How is that not helping? Your problem is that you have a display you > > can't get the supported resolutions from. What I'm suggesting allows you > > to create all the possible resolutions for that display, allowing the > > user to use the display, which is what we did for multiple drivers with > > the same problem. > > How would the possible resolutions be provided to the kernel ? Isn't it > the whole point of EDID ? > > > You seem to be set on providing the EDID to the kernel, but it's a > > terrible idea to begin with, so I'd rather discuss alternatives. > > Could you elaborate on why it is a terrible idea ? I'd be happy to continue this discussion when you'll have time. -- Regards, Laurent Pinchart