linux-kernel - Re: [Patch v6 1/7] slimbus: Device management on SLIMbus

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Message-ID: <20171013192643.lw6w2qs2bcs66hyx@rob-hp-laptop>
Date:   Fri, 13 Oct 2017 14:26:43 -0500
From:   Rob Herring <robh@...nel.org>
To:     srinivas.kandagatla@...aro.org
Cc:     gregkh@...uxfoundation.org, broonie@...nel.org,
        alsa-devel@...a-project.org, sdharia@...eaurora.org, bp@...e.de,
        poeschel@...onage.de, treding@...dia.com,
        gong.chen@...ux.intel.com, andreas.noever@...il.com,
        alan@...ux.intel.com, mathieu.poirier@...aro.org, daniel@...ll.ch,
        jkosina@...e.cz, sharon.dvir1@...l.huji.ac.il, joe@...ches.com,
        davem@...emloft.net, james.hogan@...tec.com,
        michael.opdenacker@...e-electrons.com, pawel.moll@....com,
        mark.rutland@....com, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, kheitke@...ience.com,
        linux-arm-msm@...r.kernel.org, arnd@...db.de
Subject: Re: [Patch v6 1/7] slimbus: Device management on SLIMbus

On Fri, Oct 06, 2017 at 05:51:30PM +0200, srinivas.kandagatla@...aro.org wrote:
> From: Sagar Dharia <sdharia@...eaurora.org>
> 
> SLIMbus (Serial Low Power Interchip Media Bus) is a specification
> developed by MIPI (Mobile Industry Processor Interface) alliance.
> SLIMbus is a 2-wire implementation, which is used to communicate with
> peripheral components like audio-codec.
> SLIMbus uses Time-Division-Multiplexing to accommodate multiple data
> channels, and control channel. Control channel has messages to do
> device-enumeration, messages to send/receive control-data to/from
> slimbus devices, messages for port/channel management, and messages to
> do bandwidth allocation.
> The framework supports multiple instances of the bus (1 controller per
> bus), and multiple slave devices per controller.
> 
> This patch does device enumeration, logical address assignment,
> informing device when the device reports present/absent etc.
> Reporting present may need the driver to do the needful (e.g. turning
> on voltage regulators powering the device). Additionally device is
> probed when it reports present if that device doesn't need any such
> steps mentioned above.
> 
> Signed-off-by: Sagar Dharia <sdharia@...eaurora.org>
> Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
> ---
>  Documentation/devicetree/bindings/slimbus/bus.txt |  57 ++

Split to separate patch.

>  Documentation/slimbus/summary                     | 109 ++++
>  drivers/Kconfig                                   |   2 +
>  drivers/Makefile                                  |   1 +
>  drivers/slimbus/Kconfig                           |  11 +
>  drivers/slimbus/Makefile                          |   5 +
>  drivers/slimbus/slim-core.c                       | 695 ++++++++++++++++++++++
>  include/linux/mod_devicetable.h                   |  13 +
>  include/linux/slimbus.h                           | 299 ++++++++++
>  9 files changed, 1192 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/slimbus/bus.txt
>  create mode 100644 Documentation/slimbus/summary
>  create mode 100644 drivers/slimbus/Kconfig
>  create mode 100644 drivers/slimbus/Makefile
>  create mode 100644 drivers/slimbus/slim-core.c
>  create mode 100644 include/linux/slimbus.h
> 
> diff --git a/Documentation/devicetree/bindings/slimbus/bus.txt b/Documentation/devicetree/bindings/slimbus/bus.txt
> new file mode 100644
> index 0000000..cb658bb
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/slimbus/bus.txt
> @@ -0,0 +1,57 @@
> +SLIM(Serial Low Power Interchip Media Bus) bus
> +
> +SLIMbus is a 2-wire bus, and is used to communicate with peripheral
> +components like audio-codec.
> +
> +Controller is a normal device using binding for whatever bus it is
> +on (e.g. platform bus).

I can't have a PCI based slimbus controller? "platform bus" is a 
Linuxism.

> +Required property for SLIMbus controller node:
> +- compatible	- name of SLIMbus controller following generic names
> +		recommended practice.

generic names aren't recommended. Allowed with some conditons, yes.

> +- #address-cells - should be 2

You used 4 for your controller.

> +- #size-cells	- should be 0
> +
> +No other properties are required in the SLIMbus controller bus node.

That's not a useful statement. Almost every controller probably has 
other required properties.

> +
> +Child nodes:
> +Every SLIMbus controller node can contain zero or more child nodes
> +representing slave devices on the bus. Every SLIMbus slave device is
> +uniquely determined by the enumeration address containing 4 fields:
> +Manufacturer ID, Product code, Device index, and Instance value for
> +the device.
> +If child node is not present and it is instantiated after device
> +discovery (slave device reporting itself present).
> +
> +In some cases it may be necessary to describe non-probeable device
> +details such as non-standard ways of powering up a device. In
> +such cases, child nodes for those devices will be present as
> +slaves of the slimbus-controller, as detailed below.
> +
> +Required property for SLIMbus child node if it is present:
> +- reg		- Is Duplex (Device index, Instance ID) from Enumeration
> +		  Address.
> +		  Device Index Uniquely identifies multiple Devices within
> +		  a single Component.
> +		  Instance ID Is for the cases where multiple Devices of the
> +		  same type or Class are attached to the bus.
> +
> +- compatible	-"slimMID,PID". The textual representation of Manufacturer ID,
> +	 	  Product Code, shall be in lower case hexadecimal with leading
> +		  zeroes suppressed
> +
> +SLIMbus example for Qualcomm's slimbus manager component:
> +
> +	slim@...80000 {
> +		compatible = "qcom,slim-msm";
> +		reg = <0x28080000 0x2000>,
> +		interrupts = <0 33 0>;
> +		clocks = <&lcc SLIMBUS_SRC>, <&lcc AUDIO_SLIMBUS_CLK>;
> +		clock-names = "iface_clk", "core_clk";
> +		#address-cells = <2>;
> +		#size-cells = <0>;
> +
> +		codec: wcd9310@1{

Is '1' by itself unique enough because you have 2 address cells. The 
unit-address is typically split up into fields with commas unless it's 
just a memory address. Anyway, you need to define the unit address 
format in this doc.

> +			compatible = "slim217,60"";
> +			reg = <1 0>;
> +		};
> +	};