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Date:   Thu, 24 Mar 2022 08:26:28 -0500
From:   Rob Herring <robh@kernel.org>
To:     Sui Jingfeng <15330273260@189.cn>
Cc:     Qing Zhang <zhangqing@loongson.cn>,
        David Airlie <airlied@linux.ie>,
        Jiaxun Yang <jiaxun.yang@flygoat.com>,
        linux-kernel@vger.kernel.org, Sam Ravnborg <sam@ravnborg.org>,
        Krzysztof Kozlowski <krzk@kernel.org>,
        Dan Carpenter <dan.carpenter@oracle.com>,
        devicetree@vger.kernel.org, suijingfeng <suijingfeng@loongson.cn>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        Roland Scheidegger <sroland@vmware.com>,
        Andrey Zhizhikin <andrey.zhizhikin@leica-geosystems.com>,
        dri-devel@lists.freedesktop.org,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        linux-mips@vger.kernel.org,
        "David S . Miller" <davem@davemloft.net>
Subject: Re: [PATCH v11 5/7] dt-bindings: display: Add Loongson display
 controller
Message-ID: <YjxxhNnmqteTIEOa@robh.at.kernel.org>
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 <f7eb61bc-6784-c77a-083f-7408c0a17e05@189.cn>
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On Thu, Mar 24, 2022 at 09:48:19AM +0800, Sui Jingfeng wrote:
> 
> On 2022/3/23 21:03, Rob Herring wrote:
> > On Wed, Mar 23, 2022 at 11:38:55AM +0800, Sui Jingfeng wrote:
> > > On 2022/3/23 04:55, Rob Herring wrote:
> > > > On Tue, Mar 22, 2022 at 10:33:45AM +0800, Sui Jingfeng wrote:
> > > > > On 2022/3/22 07:20, Rob Herring wrote:
> > > > > > On Tue, Mar 22, 2022 at 12:29:14AM +0800, Sui Jingfeng wrote:
> > > > > > > From: suijingfeng <suijingfeng@loongson.cn>
> > > > > > > 
> > > > > > Needs a commit message.
> > > > > > 
> > > > > > > Signed-off-by: suijingfeng <suijingfeng@loongson.cn>
> > > > > > > Signed-off-by: Sui Jingfeng <15330273260@189.cn>
> > > > > > Same person? Don't need both emails.
> > > > > Yes,? suijingfeng@loongson.cn is my company's email. But it can not be used
> > > > > to send patches to dri-devel,
> > > > > 
> > > > > when send patches with this email, the patch will not be shown on patch
> > > > > works.
> > > > > 
> > > > > Emails? are either blocked or got? rejected? by loongson's mail server.? It
> > > > > can only receive emails
> > > > > 
> > > > > from you and other people, but not dri-devel. so have to use my personal
> > > > > email(15330273260@189.cn) to send patches.
> > > > > 
> > > > > > > ---
> > > > > > >     .../loongson/loongson,display-controller.yaml | 230 ++++++++++++++++++
> > > > > > >     1 file changed, 230 insertions(+)
> > > > > > >     create mode 100644 Documentation/devicetree/bindings/display/loongson/loongson,display-controller.yaml
> > > > > > > 
> > > > > > > diff --git a/Documentation/devicetree/bindings/display/loongson/loongson,display-controller.yaml b/Documentation/devicetree/bindings/display/loongson/loongson,display-controller.yaml
> > > > > > > new file mode 100644
> > > > > > > index 000000000000..7be63346289e
> > > > > > > --- /dev/null
> > > > > > > +++ b/Documentation/devicetree/bindings/display/loongson/loongson,display-controller.yaml
> > > > > > > @@ -0,0 +1,230 @@
> > > > > > > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > > > > > > +%YAML 1.2
> > > > > > > +---
> > > > > > > +$id: http://devicetree.org/schemas/display/loongson/loongson,display-controller.yaml#
> > > > > > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > > > > > +
> > > > > > > +title: Loongson LS7A1000/LS2K1000/LS2K0500 Display Controller Device Tree Bindings
> > > > > > > +
> > > > > > > +maintainers:
> > > > > > > +  - Sui Jingfeng <suijingfeng@loongson.cn>
> > > > > > > +
> > > > > > > +description: |+
> > > > > > > +
> > > > > > > +  Loongson display controllers are simple which require scanout buffers
> > > > > > > +  to be physically contiguous. LS2K1000/LS2K0500 is a SOC, only system
> > > > > > > +  memory is available. LS7A1000/LS7A2000 is bridge chip which is equipped
> > > > > > > +  with a dedicated video RAM which is 64MB or more, precise size can be
> > > > > > > +  read from the PCI BAR 2 of the GPU device(0x0014:0x7A15) in the bridge
> > > > > > > +  chip.
> > > > > > > +
> > > > > > > +  LSDC has two display pipes, each way has a DVO interface which provide
> > > > > > > +  RGB888 signals, vertical & horizontal synchronisations, data enable and
> > > > > > > +  the pixel clock. LSDC has two CRTC, each CRTC is able to scanout from
> > > > > > > +  1920x1080 resolution at 60Hz. Each CRTC has two FB address registers.
> > > > > > > +
> > > > > > > +  For LS7A1000, there are 4 dedicated GPIOs whose control register is
> > > > > > > +  located at the DC register space. They are used to emulate two way i2c,
> > > > > > > +  One for DVO0, another for DVO1.
> > > > > > > +
> > > > > > > +  LS2K1000 and LS2K0500 SoC grab i2c adapter from other module, either
> > > > > > > +  general purpose GPIO emulated i2c or hardware i2c in the SoC.
> > > > > > > +
> > > > > > > +  LSDC's display pipeline have several components as below description,
> > > > > > > +
> > > > > > > +  The display controller in LS7A1000:
> > > > > > > +     ___________________                                     _________
> > > > > > > +    |            -------|                                   |         |
> > > > > > > +    |  CRTC0 --> | DVO0 ----> Encoder0 ---> Connector0 ---> | Monitor |
> > > > > > > +    |  _   _     -------|        ^             ^            |_________|
> > > > > > > +    | | | | |    -------|        |             |
> > > > > > > +    | |_| |_|    | i2c0 <--------+-------------+
> > > > > > > +    |            -------|
> > > > > > > +    |   DC IN LS7A1000  |
> > > > > > > +    |  _   _     -------|
> > > > > > > +    | | | | |    | i2c1 <--------+-------------+
> > > > > > > +    | |_| |_|    -------|        |             |             _________
> > > > > > > +    |            -------|        |             |            |         |
> > > > > > > +    |  CRTC1 --> | DVO1 ----> Encoder1 ---> Connector1 ---> |  Panel  |
> > > > > > > +    |            -------|                                   |_________|
> > > > > > > +    |___________________|
> > > > > > > +
> > > > > > > +  Simple usage of LS7A1000 with LS3A4000 CPU:
> > > > > > > +
> > > > > > > +    +------+            +-----------------------------------+
> > > > > > > +    | DDR4 |            |  +-------------------+            |
> > > > > > > +    +------+            |  | PCIe Root complex |   LS7A1000 |
> > > > > > > +       || MC0           |  +--++---------++----+            |
> > > > > > > +  +----------+  HT 3.0  |     ||         ||                 |
> > > > > > > +  | LS3A4000 |<-------->| +---++---+  +--++--+    +---------+   +------+
> > > > > > > +  |   CPU    |<-------->| | GC1000 |  | LSDC |<-->| DDR3 MC |<->| VRAM |
> > > > > > > +  +----------+          | +--------+  +-+--+-+    +---------+   +------+
> > > > > > > +       || MC1           +---------------|--|----------------+
> > > > > > > +    +------+                            |  |
> > > > > > > +    | DDR4 |          +-------+   DVO0  |  |  DVO1   +------+
> > > > > > > +    +------+   VGA <--|ADV7125|<--------+  +-------->|TFP410|--> DVI/HDMI
> > > > > > > +                      +-------+                      +------+
> > > > > > > +
> > > > > > > +  The display controller in LS2K1000/LS2K0500:
> > > > > > > +     ___________________                                     _________
> > > > > > > +    |            -------|                                   |         |
> > > > > > > +    |  CRTC0 --> | DVO0 ----> Encoder0 ---> Connector0 ---> | Monitor |
> > > > > > > +    |  _   _     -------|        ^              ^           |_________|
> > > > > > > +    | | | | |           |        |              |
> > > > > > > +    | |_| |_|           |     +------+          |
> > > > > > > +    |                   <---->| i2c0 |<---------+
> > > > > > > +    |   DC IN LS2K1000  |     +------+
> > > > > > > +    |  _   _            |     +------+
> > > > > > > +    | | | | |           <---->| i2c1 |----------+
> > > > > > > +    | |_| |_|           |     +------+          |            _________
> > > > > > > +    |            -------|        |              |           |         |
> > > > > > > +    |  CRTC1 --> | DVO1 ----> Encoder1 ---> Connector1 ---> |  Panel  |
> > > > > > > +    |            -------|                                   |_________|
> > > > > > > +    |___________________|
> > > > > > > +
> > > > > > > +properties:
> > > > > > > +  $nodename:
> > > > > > > +    pattern: "^display-controller@[0-9a-f],[0-9a-f]$"
> > > > > > > +
> > > > > > > +  compatible:
> > > > > > > +    oneOf:
> > > > > > > +      - items:
> > > > > > > +          - enum:
> > > > > > > +              - loongson,ls7a1000-dc
> > > > > > > +              - loongson,ls2k1000-dc
> > > > > > > +              - loongson,ls2k0500-dc
> > > > > > > +
> > > > > > > +  reg:
> > > > > > > +    maxItems: 1
> > > > > > > +
> > > > > > > +  interrupts:
> > > > > > > +    maxItems: 1
> > > > > > > +
> > > > > > > +  '#address-cells':
> > > > > > > +    const: 1
> > > > > > > +
> > > > > > > +  '#size-cells':
> > > > > > > +    const: 0
> > > > > > > +
> > > > > > > +  i2c-gpio@0:
> > > > > > > +    description: |
> > > > > > > +      Built-in GPIO emulate i2c exported for external display bridge
> > > > > > If you have i2c-gpio, that belongs at the DT top-level, not here.
> > > > > > 
> > > > > > > +      configuration, onitor detection and edid read back etc, for ls7a1000
> > > > > > > +      only. Its compatible must be lsdc,i2c-gpio-0. The reg property can be
> > > > > > No, there's a defined i2c-gpio compatible already.
> > > > > This is different from the i2c-gpio already defined under drivers/i2c/busses/i2c-gpio.c,
> > > > > By design, my i2c-gpio is vendor specific properties, lsdc device driver create the i2c
> > > > > adapter at runtime. These are 4 dedicated GPIOs whose control register is located at the
> > > > > LSDC register space, not general purpose GPIOs with separate control register resource.
> > > > > So i think it is the child node of?display-controller@6,1,?it belongs to LSDC.
> > > > > It seems that put it at the DT top-level break the hierarchy and relationship.
> > > > Okay, I see. Then just 'i2c' for the node names. You need a reference to
> > > > i2c-controller.yaml for these nodes too.
> > > > 
> > > > The compatible should not have an index in it.
> > > OK, i will fix this at the next version. thanks.
> > > > > > > +      used to specify a I2c adapter bus number, if you don't specify one
> > > > > > > +      i2c driver core will dynamically assign a bus number. Please specify
> > > > > > Bus numbers are a linux detail not relevant to DT binding.
> > > > > > 
> > > > > > > +      it only when its bus number matters. Bus number greater than 6 is safe
> > > > > > > +      because ls7a1000 bridge have 6 hardware I2C controller integrated.
> > > > > > > +
> > > > > > > +  i2c-gpio@1:
> > > > > > > +    description: |
> > > > > > > +      Built-in GPIO emulate i2c exported for external display bridge
> > > > > > > +      configuration, onitor detection and edid read back etc, for ls7a1000
> > > > > > > +      only. Its compatible must be lsdc,i2c-gpio-1.
> > > > > > > +
> > > > > > > +  ports:
> > > > > > > +    $ref: /schemas/graph.yaml#/properties/ports
> > > > > > > +
> > > > > > > +    properties:
> > > > > > > +      port@0:
> > > > > > > +        $ref: /schemas/graph.yaml#/properties/port
> > > > > > > +        description: output port node connected with DPI panels or external encoders, with only one endpoint.
> > > > > > > +
> > > > > > > +      port@1:
> > > > > > > +        $ref: /schemas/graph.yaml#/properties/port
> > > > > > > +        description: output port node connected with DPI panels or external encoders, with only one endpoint.
> > > > > > > +
> > > > > > > +    required:
> > > > > > > +      - port@0
> > > > > > > +      - port@1
> > > > > > > +
> > > > > > > +required:
> > > > > > > +  - compatible
> > > > > > > +  - reg
> > > > > > > +  - interrupts
> > > > > > > +  - ports
> > > > > > > +
> > > > > > > +additionalProperties: false
> > > > > > > +
> > > > > > > +examples:
> > > > > > > +  - |
> > > > > > > +    #include <dt-bindings/interrupt-controller/irq.h>
> > > > > > > +    bus {
> > > > > > > +
> > > > > > > +        #address-cells = <3>;
> > > > > > > +        #size-cells = <2>;
> > > > > > > +        #interrupt-cells = <2>;
> > > > > > > +
> > > > > > > +        display-controller@6,1 {
> > > > > > > +            compatible = "loongson,ls7a1000-dc";
> > > > > > > +            reg = <0x3100 0x0 0x0 0x0 0x0>;
> > > > > > > +            interrupts = <28 IRQ_TYPE_LEVEL_HIGH>;
> > > > > > > +
> > > > > > > +            #address-cells = <1>;
> > > > > > > +            #size-cells = <0>;
> > > > > > > +
> > > > > > > +            i2c-gpio@0 {
> > > > > > > +                compatible = "lsdc,i2c-gpio-0";
> > > > > > > +                reg = <6>;
> > > > 'reg' needs to be documented with some description of what 6 and 7
> > > > represent. If they are the control register offset, then make the
> > > > address translatable (use 'ranges' and define the size).
> > > By design, the reg property is used to specify a I2c adapter bus number,
> > > if we don't specify one, i2c driver core will dynamically assign a bus number.
> > > then the nr of the i2c adapter will started from 0. I want is start from 6
> > > to avoid potential conflict feature hardware I2C driver.
> > > 
> > > Because LS7A1000 bridge chip have 6 hardware I2C controller integrated,
> > > but its driver is not up-streamed yet. By default these hardware I2C controller's
> > > nr is started from 0.
> > Linux's numbering doesn't belong in DT. So no, you can't use 'reg' in
> > that way.
> Then,? can i use something like lsdc,nr = <6> ?
> > > Even through i2c driver core can dynamically generate a number, i still want it
> > > to be fixed and keep consistent and explicit. That is, i2c6 is for display pipe 0,
> > > i2c7 is for display pipe 1. This follow the convention and flexible enough.
> > You may want that, but that is not how the kernel works. Specific
> > numbers are not guaranteed. I'm sure you've seen this for disks, network
> > interfaces, etc.
> > 
> > Rob
> 
> 2c_bit_add_numbered_bus() will guarantee it for you as long as If no devices
> have pre-been declared for this bus.
> 
> you can read the comment of 2c_bit_add_numbered_bus() at
> drivers/i2c/i2c-core-base.c

I didn't say it wasn't possible. It is not best practice. Grep 
i2c_bit_add_numbered_bus and see how many users there are. Even if the 
kernel allows specifying bus numbers, your Linux bus numbers don't 
belong in DT.

Rob