From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from moutng.kundenserver.de ([212.227.126.171]:51495 "EHLO moutng.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932674Ab2GKO1z (ORCPT ); Wed, 11 Jul 2012 10:27:55 -0400 Date: Wed, 11 Jul 2012 16:27:52 +0200 (CEST) From: Guennadi Liakhovetski To: Linux Media Mailing List cc: Laurent Pinchart , Magnus Damm Subject: [RFC] media DT bindings Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-media-owner@vger.kernel.org List-ID: Hi all Background ========== With ARM adoption of flat Device Trees a need arises to move platform device descriptions and their data from platform files to DT. This has also to be done for media devices, e.g., video capture and output interfaces, data processing devices, camera sensors, TV decoders and encoders. This RFC is trying to spawn a discussion to define standard V4L DT bindings. The first version will concentrate on the capture path, mostly taking care of simple capture-interface - camera sensor / TV decoder configurations. Since the author is not working intensively yet with the Media Controller API, pad-level configuration, these topics might be underrepresented in this RFC. I hope others, actively working in these areas, will fill me in on them. Overview ======== As mentioned above, typical configurations, that we'll be dealing with consist of a DMA data capture engine, one or more data sources like camera sensors, possibly some data processing units. Data capture and processing engines are usually platform devices, whereas data source devices are typically I2C slaves. Apart from defining each device we'll also describe connections between them as well as properties of those connections. Capture devices ============================== These are usually platform devices, integrated into respective SoCs. There also exist external image processing devices, but they are rare. Obvious differences between them and integrated devices include a different bus attribution and a need to explicitly describe the connection to the SoC. As far as capture devices are concerned, their configuration will typically include a few device-specific bindings, as well as standard ones. Standard bindings will include the usual "reg," "interrupts," "clock-frequency" properties. It is more complex to describe external links. We need to describe configurations, used with various devices, attached to various pads. It is proposed to describe such links as child nodes. Each such link will reference a client pad, a local pad and specify the bus configuration. The media bus can be either parallel or serial, e.g., MIPI CSI-2. It is proposed to describe both the bus-width in the parallel case and the number of lanes in the serial case, using the standard "bus-width" property. On the parallel bus common properties include signal polarities, possibly data line shift (8 if lines 15:8 are used, 2 if 9:2, and 0 if lines 7:0), protocol (e.g., BT.656). Additionally device-specific properties can be defined. A MIPI CSI-2 bus common properties would include, apart from the number of lanes, routed to that client, the clock frequency, a channel number, possibly CRC and ECC flags. An sh-mobile CEU DT node could look like ceu0@0xfe910000 = { compatible = "renesas,sh-mobile-ceu"; reg = <0xfe910000 0xa0>; interrupts = <0x880>; bus-width = <16>; /* #lines routed on the board */ clock-frequency = <50000000>; /* max clock */ #address-cells = <1>; #size-cells = <0>; ... ov772x-1 = { reg = <0>; client = <&ov772x@0x21-0>; local-pad = "parallel-sink"; remote-pad = "parallel-source"; bus-width = <8>; /* used data lines */ data-shift = <0>; /* lines 7:0 are used */ hsync-active = <1>; /* active high */ vsync-active = <1>; /* active high */ pclk-sample = <1>; /* rising */ clock-frequency = <24000000>; }; }; Client devices ============== Client nodes are children on their respective busses, e.g., i2c. This placement leads to these devices being possibly probed before respective host interfaces, which will fail due to known reasons. Therefore client drivers have to be adapted to request a delayed probing, as long as the respective video host hasn't probed. Client nodes will include all the properties, usual for their busses. Additionally they will specify properties private to this device type and common for all V4L2 client devices - device global and per-link. I think, we should make it possible to define client devices, that can at run-time be connected to different sinks, even though such configurations might not be very frequent. To achieve this we also specify link information in child devices, similar to those in host nodes above. This also helps uniformity and will let us implement and use a universal link-binding parser. So, a node, that has been referenced above could look like ov772x@0x21-0 = { compatible = "omnivision,ov772x"; reg = <0x21>; vdd-supply = <®ulator>; bus-width = <10>; #address-cells = <1>; #size-cells = <0>; ... ceu0-1 = { reg = <0>; media-parent = <&ceu0@0xfe910000>; bus-width = <8>; hsync-active = <1>; vsync-active = <0>; /* who came up with an inverter here?... */ pclk-sample = <1>; }; }; Data processors =============== Data processing modules include resizers, codecs, rotators, serialisers, etc. A node for an sh-mobile CSI-2 subdevice could look like csi2@0xffc90000 = { compatible = "renesas,sh-mobile-csi2"; reg = <0xffc90000 0x1000>; interrupts = <0x17a0>; bus-width = <4>; clock-frequency = <30000000>; ... imx074-1 = { client = <&imx074@0x1a-0>; local-pad = "csi2-sink"; remote-pad = "csi2-source"; bus-width = <2>; clock-frequency = <25000000>; csi2-crc; csi2-ecc; sh-csi2,phy = <0>; }; ceu0 = { media-parent = <&ceu0@0xfe910000>; immutable; }; }; The respective child binding in the CEU node could then look like csi2-1 = { reg = <1>; client = <&csi2@0xffc90000>; immutable; }; Comments welcome. Thanks Guennadi --- Guennadi Liakhovetski, Ph.D. Freelance Open-Source Software Developer http://www.open-technology.de/