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 A3ACA191; Sun, 26 Apr 2026 13:27:23 +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=1777210046; cv=none; b=j6YD1W6EvSn3xdoNBfrJN0UpgpUMrbA1rqSODQMs7mvncKzOc97W+sLlG3xJrSEWkY77p1a9qteL50yxnpa2C5lZykTUVfGz7wO7u15D0GFD1uoAvce5f0cfP6PujXDhk5IqYb6qYA3v2nU7nIcxjpqHBVEWXpL+n1YJqnAaVWc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777210046; c=relaxed/simple; bh=AImdYVRVxu5KDaS0wYHMilfThx6b/J7M7IYbo4FUIic=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=LSTq4Yu/T58dgJ2MajQHFkQOPvqG2gbY/iJhuhaqBvOqIyaVsA2L6Vh3lQuNFiYPXXcCzlMe8svw6DX5Jny8A+YOD2sJk9tZgS0Kfp8I9bH87/ZI2NnnKNVGBD4uWAIiBAYy/qKYXUsOr49VfAGdLHRIUtHFkOozW6RwGc1LnVM= 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=V4Lgyvz+; 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="V4Lgyvz+" Received: from killaraus.ideasonboard.com (2001-14ba-703d-e500--2a1.rev.dnainternet.fi [IPv6:2001:14ba:703d:e500::2a1]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id 36BCF6A6; Sun, 26 Apr 2026 15:25:39 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1777209939; bh=AImdYVRVxu5KDaS0wYHMilfThx6b/J7M7IYbo4FUIic=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=V4Lgyvz+LZ/B8NucZ0Tq9FVaEOSNosKAzOGtypyt0aopXlHtPJ5LgFoqccCr2/Ebk 05wMugBV4SQYdxtJ4jryIdOh5QNeSC5BhErZRAvpDAdYVz6v5ePwa04f6HAA2YihYf t2MstkfWay9RaYZcKTRJ2Jf64UeuJlD0IavR7VGU= Date: Sun, 26 Apr 2026 16:27:19 +0300 From: Laurent Pinchart To: Heiko Stuebner Cc: Dmitry Baryshkov , Dennis Gilmore , Andrzej Hajda , Neil Armstrong , Robert Foss , Rob Herring , Krzysztof Kozlowski , Conor Dooley , Jonas Karlman , Jernej Skrabec , Maxime Ripard , Alexey Charkov , devicetree@vger.kernel.org, linux-rockchip@lists.infradead.org, linux-arm-kernel@lists.infradead.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v8 3/6] drm/bridge: simple: Add the Lontium LT8711UXD DP-to-HDMI bridge Message-ID: <20260426132719.GD2964234@killaraus.ideasonboard.com> References: <20260425031011.2529364-1-dennis@ausil.us> <20260425234845.GC2964234@killaraus.ideasonboard.com> <6519122.LvFx2qVVIh@phil> 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 Content-Transfer-Encoding: 8bit In-Reply-To: <6519122.LvFx2qVVIh@phil> On Sun, Apr 26, 2026 at 11:54:57AM +0200, Heiko Stuebner wrote: > Am Sonntag, 26. April 2026, 01:48:45 Mitteleuropäische Sommerzeit schrieb Laurent Pinchart: > > On Sun, Apr 26, 2026 at 12:44:59AM +0300, Dmitry Baryshkov wrote: > > > On Sat, Apr 25, 2026 at 01:10:02PM -0500, Dennis Gilmore wrote: > > > > On Sat, Apr 25, 2026 at 9:24 AM Dmitry Baryshkov wrote: > > > > > On Sat, Apr 25, 2026 at 02:28:44PM +0300, Laurent Pinchart wrote: > > > > > > Hi Dennis, > > > > > > > > > > > > Thank you for the patch. > > > > > > > > > > > > On Fri, Apr 24, 2026 at 10:10:08PM -0500, Dennis Gilmore wrote: > > > > > > > The Lontium LT8711UXD is a high performance two lane Type-C/DP1.4 > > > > > > > to HDMI2.0 converter, designed to connect a USB Type-C source or > > > > > > > a DP1.4 source to an HDMI2.0 sink. > > > > > > > > > > > > As far as I can tell, the LT8711UXD has an I2C control interface. > > > > > > Shouldn't it be an I2C device ? > > > > > > > > > > From the datasheet: > > > > > > > > > > The device is capable of automatic operation which is > > > > > enabled by an integrated microprocessor that uses an > > > > > embedded SPI flash for firmware storage. System control > > > > > is also available through the use of a dedicated > > > > > configuration I2C slave interface. > > > > > > > > > > My guess was that it can either be an I2C device or it can function as a > > > > > simple platdev with no I2C controls. Please correct me if my > > > > > understanding was wrong. > > > > > > > > > > But now looking at the schematics, it seems to be connected to I2C6. > > > > > Which means that it should be desribed (and bound) as such. > > > > > > > > Hi Dmitry and Laurent, > > > > > > > > While the schematic shows that it can use I2C and has been wired up, > > > > it also shows that both MODE_SEL and I2C_ADDR have unpopulated 10k > > > > resistors; as a result, MODE_SEL is connected directly to GND, > > looking at the schematics linked in the board patch, I somehow see > both R9 (mode_sel -> vcc3v3_io) but also R17 (mode_sel -> gnd) marked > as 10K.nc ? > > > > > putting > > > > the bridge in autonomous mode. I confirmed this by running `i2cdetect > > > > -r -y 6`, with the only device on the bus being the HYM8563 RTC at > > > > 0x51. Without reworking the board, the device is not directly > > > > controllable and just runs autonomously. > > > > > > I think it would be nice to mention: > > > - In the commit for the bindings, that the device can be running > > > uncontrolled or it can be attached over I2C, bindings describe the > > > uncontrolled mode. > > > - In this commit message, the same. > > > - In the commit message for the board DT mention your findings about the > > > board, mention soldering R9 or R17 (which one?) and R27. > > > > Additionally, how are we going to handle boards where the device > > operates in I2C mode ? Will we use a different compatible string (maybe > > "lontium,lt8711uxd-i2c") ? If DT maintainers are fine with that, I have > > no objection to this patch. > > I would assume it'd be more the dt-maintainers objecting? Yes, probably :-) My main concern here is making sure we're not cornering ourselves. > I.e. the two different bindings for the same hardware and leaking Linux > implementation-specifics into the binding. > > I'm don't have deep insight into the i2c framework, but I guess the i2c > device probe does not need to talk to an i2c device due to resources > needing setup. Does the i2c core need to talk to the device at all? > > Because otherwise, you could just do a regular i2c device (the routing > for everything is there afterall), add a lontium,automatic-mode; flag > to the node to denote mode. That would work in this case, but if we have a board where the I2C lines are really not routed, we would have to invent a fake connection to an I2C controller. That's not very nice. There seem to be precedents for devices that can be controlled through either I2C or SPI. See for instance Documentation/devicetree/bindings/net/nfc/st,st-nci.yaml that defines two compatible strings for the same device, "st,st21nfcb-i2c" and "st,st21nfcb-spi". I don't know if that's the best practice recommended by the DT maintainers, or a hack that slipped through. > And if for whatever reason a variant appears with the lines connected > you can just modifiy the DT via an overlay? -- Regards, Laurent Pinchart