Re: [PATCH v3 8/9] drm/doc: Add initial komeda driver documentation

[Liviu Dudau]

On Fri, Dec 21, 2018 at 10:00:49AM +0000, james qian wang (Arm Technology China) wrote:
> v2: Some editing changes according to Randy Dunlap's comments
> 
> Signed-off-by: James (Qian) Wang <james.qian.wang@xxxxxxx>

Reviewed-by: Liviu Dudau <liviu.dudau@xxxxxxx>

> ---
>  Documentation/gpu/drivers.rst    |   1 +
>  Documentation/gpu/komeda-kms.rst | 488 +++++++++++++++++++++++++++++++
>  2 files changed, 489 insertions(+)
>  create mode 100644 Documentation/gpu/komeda-kms.rst
> 
> diff --git a/Documentation/gpu/drivers.rst b/Documentation/gpu/drivers.rst
> index 7c1672118a73..978e6da9bbff 100644
> --- a/Documentation/gpu/drivers.rst
> +++ b/Documentation/gpu/drivers.rst
> @@ -17,6 +17,7 @@ GPU Driver Documentation
>     vkms
>     bridge/dw-hdmi
>     xen-front
> +   komeda-kms
>  
>  .. only::  subproject and html
>  
> diff --git a/Documentation/gpu/komeda-kms.rst b/Documentation/gpu/komeda-kms.rst
> new file mode 100644
> index 000000000000..b08da1cffecc
> --- /dev/null
> +++ b/Documentation/gpu/komeda-kms.rst
> @@ -0,0 +1,488 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +==============================
> + drm/komeda Arm display driver
> +==============================
> +
> +The drm/komeda driver supports the Arm display processor D71 and later products,
> +this document gives a brief overview of driver design: how it works and why
> +design it like that.
> +
> +Overview of D71 like display IPs
> +================================
> +
> +From D71, Arm display IP begins to adopt a flexible and modularized
> +architecture. A display pipeline is made up of multiple individual and
> +functional pipeline stages called components, and every component has some
> +specific capabilities that can give the flowed pipeline pixel data a
> +particular processing.
> +
> +Typical D71 components:
> +
> +Layer
> +-----
> +Layer is the first pipeline stage, which prepares the pixel data for the next
> +stage. It fetches the pixel from memory, decodes it if it's AFBC, rotates the
> +source image, unpacks or converts YUV pixels to the device internal RGB pixels,
> +then adjusts the color_space of pixels if needed.
> +
> +Scaler
> +------
> +As its name suggests, scaler takes responsibility for scaling, and D71 also
> +supports image enhancements by scaler.
> +The usage of scaler is very flexible and can be connected to layer output
> +for layer scaling, or connected to compositor and scale the whole display
> +frame and then feed the output data into wb_layer which will then write it
> +into memory.
> +
> +Compositor (compiz)
> +-------------------
> +Compositor blends multiple layers or pixel data flows into one single display
> +frame. its output frame can be fed into post image processor for showing it on
> +the monitor or fed into wb_layer and written to memory at the same time.
> +user can also insert a scaler between compositor and wb_layer to down scale
> +the display frame first and and then write to memory.
> +
> +Writeback Layer (wb_layer)
> +--------------------------
> +Writeback layer does the opposite things of Layer, which connects to compiz
> +and writes the composition result to memory.
> +
> +Post image processor (improc)
> +-----------------------------
> +Post image processor adjusts frame data like gamma and color space to fit the
> +requirements of the monitor.
> +
> +Timing controller (timing_ctrlr)
> +--------------------------------
> +Final stage of display pipeline, Timing controller is not for the pixel
> +handling, but only for controlling the display timing.
> +
> +Merger
> +------
> +D71 scaler mostly only has the half horizontal input/output capabilities
> +compared with Layer, like if Layer supports 4K input size, the scaler only can
> +support 2K input/output in the same time. To achieve the ful frame scaling, D71
> +introduces Layer Split, which splits the whole image to two half parts and feeds
> +them to two Layers A and B, and does the scaling independently. After scaling
> +the result need to be fed to merger to merge two part images together, and then
> +output merged result to compiz.
> +
> +Splitter
> +--------
> +Similar to Layer Split, but Splitter is used for writeback, which splits the
> +compiz result to two parts and then feed them to two scalers.
> +
> +Possible D71 Pipeline usage
> +===========================
> +
> +Benefitting from the modularized architecture, D71 pipelines can be easily
> +adjusted to fit different usages. And D71 has two pipelines, which support two
> +types of working mode:
> +
> +-   Dual display mode
> +    Two pipelines work independently and separately to drive two display outputs.
> +
> +-   Single display mode
> +    Two pipelines work together to drive only one display output.
> +
> +    On this mode, pipeline_B doesn't work indenpendently, but outputs its
> +    composition result into pipeline_A, and its pixel timing also derived from
> +    pipeline_A.timing_ctrlr. The pipeline_B works just like a "slave" of
> +    pipeline_A(master)
> +
> +Single pipeline data flow
> +-------------------------
> +
> +.. kernel-render:: DOT
> +   :alt: Single pipeline digraph
> +   :caption: Single pipeline data flow
> +
> +   digraph single_ppl {
> +      rankdir=LR;
> +
> +      subgraph {
> +         "Memory";
> +         "Monitor";
> +      }
> +
> +      subgraph cluster_pipeline {
> +          style=dashed
> +          node [shape=box]
> +          {
> +              node [bgcolor=grey style=dashed]
> +              "Scaler-0";
> +              "Scaler-1";
> +              "Scaler-0/1"
> +          }
> +
> +         node [bgcolor=grey style=filled]
> +         "Layer-0" -> "Scaler-0"
> +         "Layer-1" -> "Scaler-0"
> +         "Layer-2" -> "Scaler-1"
> +         "Layer-3" -> "Scaler-1"
> +
> +         "Layer-0" -> "Compiz"
> +         "Layer-1" -> "Compiz"
> +         "Layer-2" -> "Compiz"
> +         "Layer-3" -> "Compiz"
> +         "Scaler-0" -> "Compiz"
> +         "Scaler-1" -> "Compiz"
> +
> +         "Compiz" -> "Scaler-0/1" -> "Wb_layer"
> +         "Compiz" -> "Improc" -> "Timing Controller"
> +      }
> +
> +      "Wb_layer" -> "Memory"
> +      "Timing Controller" -> "Monitor"
> +   }
> +
> +Dual pipeline with Slave enabled
> +--------------------------------
> +
> +.. kernel-render:: DOT
> +   :alt: Slave pipeline digraph
> +   :caption: Slave pipeline enabled data flow
> +
> +   digraph slave_ppl {
> +      rankdir=LR;
> +
> +      subgraph {
> +         "Memory";
> +         "Monitor";
> +      }
> +      node [shape=box]
> +      subgraph cluster_pipeline_slave {
> +          style=dashed
> +          label="Slave Pipeline_B"
> +          node [shape=box]
> +          {
> +              node [bgcolor=grey style=dashed]
> +              "Slave.Scaler-0";
> +              "Slave.Scaler-1";
> +          }
> +
> +         node [bgcolor=grey style=filled]
> +         "Slave.Layer-0" -> "Slave.Scaler-0"
> +         "Slave.Layer-1" -> "Slave.Scaler-0"
> +         "Slave.Layer-2" -> "Slave.Scaler-1"
> +         "Slave.Layer-3" -> "Slave.Scaler-1"
> +
> +         "Slave.Layer-0" -> "Slave.Compiz"
> +         "Slave.Layer-1" -> "Slave.Compiz"
> +         "Slave.Layer-2" -> "Slave.Compiz"
> +         "Slave.Layer-3" -> "Slave.Compiz"
> +         "Slave.Scaler-0" -> "Slave.Compiz"
> +         "Slave.Scaler-1" -> "Slave.Compiz"
> +      }
> +
> +      subgraph cluster_pipeline_master {
> +          style=dashed
> +          label="Master Pipeline_A"
> +          node [shape=box]
> +          {
> +              node [bgcolor=grey style=dashed]
> +              "Scaler-0";
> +              "Scaler-1";
> +              "Scaler-0/1"
> +          }
> +
> +         node [bgcolor=grey style=filled]
> +         "Layer-0" -> "Scaler-0"
> +         "Layer-1" -> "Scaler-0"
> +         "Layer-2" -> "Scaler-1"
> +         "Layer-3" -> "Scaler-1"
> +
> +         "Slave.Compiz" -> "Compiz"
> +         "Layer-0" -> "Compiz"
> +         "Layer-1" -> "Compiz"
> +         "Layer-2" -> "Compiz"
> +         "Layer-3" -> "Compiz"
> +         "Scaler-0" -> "Compiz"
> +         "Scaler-1" -> "Compiz"
> +
> +         "Compiz" -> "Scaler-0/1" -> "Wb_layer"
> +         "Compiz" -> "Improc" -> "Timing Controller"
> +      }
> +
> +      "Wb_layer" -> "Memory"
> +      "Timing Controller" -> "Monitor"
> +   }
> +
> +Sub-pipelines for input and output
> +----------------------------------
> +
> +A complete display pipeline can be easily divided into three sub-pipelines
> +according to the in/out usage.
> +
> +Layer(input) pipeline
> +~~~~~~~~~~~~~~~~~~~~~
> +
> +.. kernel-render:: DOT
> +   :alt: Layer data digraph
> +   :caption: Layer (input) data flow
> +
> +   digraph layer_data_flow {
> +      rankdir=LR;
> +      node [shape=box]
> +
> +      {
> +         node [bgcolor=grey style=dashed]
> +           "Scaler-n";
> +      }
> +
> +      "Layer-n" -> "Scaler-n" -> "Compiz"
> +   }
> +
> +.. kernel-render:: DOT
> +   :alt: Layer Split digraph
> +   :caption: Layer Split pipeline
> +
> +   digraph layer_data_flow {
> +      rankdir=LR;
> +      node [shape=box]
> +
> +      "Layer-0/1" -> "Scaler-0" -> "Merger"
> +      "Layer-2/3" -> "Scaler-1" -> "Merger"
> +      "Merger" -> "Compiz"
> +   }
> +
> +Writeback(output) pipeline
> +~~~~~~~~~~~~~~~~~~~~~~~~~~
> +.. kernel-render:: DOT
> +   :alt: writeback digraph
> +   :caption: Writeback(output) data flow
> +
> +   digraph writeback_data_flow {
> +      rankdir=LR;
> +      node [shape=box]
> +
> +      {
> +         node [bgcolor=grey style=dashed]
> +           "Scaler-n";
> +      }
> +
> +      "Compiz" -> "Scaler-n" -> "Wb_layer"
> +   }
> +
> +.. kernel-render:: DOT
> +   :alt: split writeback digraph
> +   :caption: Writeback(output) Split data flow
> +
> +   digraph writeback_data_flow {
> +      rankdir=LR;
> +      node [shape=box]
> +
> +      "Compiz" -> "Splitter"
> +      "Splitter" -> "Scaler-0" -> "Merger"
> +      "Splitter" -> "Scaler-1" -> "Merger"
> +      "Merger" -> "Wb_layer"
> +   }
> +
> +Display output pipeline
> +~~~~~~~~~~~~~~~~~~~~~~~
> +.. kernel-render:: DOT
> +   :alt: display digraph
> +   :caption: display output data flow
> +
> +   digraph single_ppl {
> +      rankdir=LR;
> +      node [shape=box]
> +
> +      "Compiz" -> "Improc" -> "Timing Controller"
> +   }
> +
> +In the following section we'll see these three sub-pipelines will be handled
> +by KMS-plane/wb_conn/crtc respectively.
> +
> +Komeda Resource abstraction
> +===========================
> +
> +struct komeda_pipeline/component
> +--------------------------------
> +
> +To fully utilize and easily access/configure the HW, the driver side also uses
> +a similar architecture: Pipeline/Component to describe the HW features and
> +capabilities, and a specific component includes two parts:
> +
> +-  Data flow controlling.
> +-  Specific component capabilities and features.
> +
> +So the driver defines a common header struct komeda_component to describe the
> +data flow control and all specific components are a subclass of this base
> +structure.
> +
> +.. kernel-doc:: drivers/gpu/drm/arm/display/komeda/komeda_pipeline.h
> +   :internal:
> +
> +Resource discovery and initialization
> +=====================================
> +
> +Pipeline and component are used to describe how to handle the pixel data. We
> +still need a @struct komeda_dev to describe the whole view of the device, and
> +the control-abilites of device.
> +
> +We have &komeda_dev, &komeda_pipeline, &komeda_component. Now fill devices with
> +pipelines. Since komeda is not for D71 only but also intended for later products,
> +of course weâd better share as much as possible between different products. To
> +achieve this, split the komeda device into two layers: CORE and CHIP.
> +
> +-   CORE: for common features and capabilities handling.
> +-   CHIP: for register programing and HW specific feature (limitation) handling.
> +
> +CORE can access CHIP by three chip function structures:
> +
> +-   struct komeda_dev_funcs
> +-   struct komeda_pipeline_funcs
> +-   struct komeda_component_funcs
> +
> +.. kernel-doc:: drivers/gpu/drm/arm/display/komeda/komeda_dev.h
> +   :internal:
> +
> +Format handling
> +===============
> +
> +.. kernel-doc:: drivers/gpu/drm/arm/display/komeda/komeda_format_caps.h
> +   :internal:
> +.. kernel-doc:: drivers/gpu/drm/arm/display/komeda/komeda_framebuffer.h
> +   :internal:
> +
> +Attach komeda_dev to DRM-KMS
> +============================
> +
> +Komeda abstracts resources by pipeline/component, but DRM-KMS uses
> +crtc/plane/connector. One KMS-obj cannot represent only one single component,
> +since the requirements of a single KMS object cannot simply be achieved by a
> +single component, usually that needs multiple components to fit the requirement.
> +Like set mode, gamma, ctm for KMS all target on CRTC-obj, but komeda needs
> +compiz, improc and timing_ctrlr to work together to fit these requirements.
> +And a KMS-Plane may require multiple komeda resources: layer/scaler/compiz.
> +
> +So, one KMS-Obj represents a sub-pipeline of komeda resources.
> +
> +-   Plane: `Layer(input) pipeline`_
> +-   Wb_connector: `Writeback(output) pipeline`_
> +-   Crtc: `Display output pipeline`_
> +
> +So, for komeda, we treat KMS crtc/plane/connector as users of pipeline and
> +component, and at any one time a pipeline/component only can be used by one
> +user. And pipeline/component will be treated as private object of DRM-KMS; the
> +state will be managed by drm_atomic_state as well.
> +
> +How to map plane to Layer(input) pipeline
> +-----------------------------------------
> +
> +Komeda has multiple Layer input pipelines, see:
> +-   `Single pipeline data flow`_
> +-   `Dual pipeline with Slave enabled`_
> +
> +The easiest way is binding a plane to a fixed Layer pipeline, but consider the
> +komeda capabilities:
> +
> +-   Layer Split, See `Layer(input) pipeline`_
> +
> +    Layer_Split is quite complicated feature, which splits a big image into two
> +    parts and handles it by two layers and two scalers individually. But it
> +    imports an edge problem or effect in the middle of the image after the split.
> +    To avoid such a problem, it needs a complicated Split calculation and some
> +    special configurations to the layer and scaler. We'd better hide such HW
> +    related complexity to user mode.
> +
> +-   Slave pipeline, See `Dual pipeline with Slave enabled`_
> +
> +    Since the compiz component doesn't output alpha value, the slave pipeline
> +    only can be used for bottom layers composition. The komeda driver wants to
> +    hide this limitation to the user. The way to do this is to pick a suitable
> +    Layer according to plane_state->zpos.
> +
> +So for komeda, the KMS-plane doesn't represent a fixed komeda layer pipeline,
> +but multiple Layers with same capabilities. Komeda will select one or more
> +Layers to fit the requirement of one KMS-plane.
> +
> +Make component/pipeline to be drm_private_obj
> +---------------------------------------------
> +
> +Add :c:type:`drm_private_obj` to :c:type:`komeda_component`, :c:type:`komeda_pipeline`
> +
> +.. code-block:: c
> +
> +    struct komeda_component {
> +        struct drm_private_obj obj;
> +        ...
> +    }
> +
> +    struct komeda_pipeline {
> +        struct drm_private_obj obj;
> +        ...
> +    }
> +
> +Tracking component_state/pipeline_state by drm_atomic_state
> +-----------------------------------------------------------
> +
> +Add :c:type:`drm_private_state` and user to :c:type:`komeda_component_state`,
> +:c:type:`komeda_pipeline_state`
> +
> +.. code-block:: c
> +
> +    struct komeda_component_state {
> +        struct drm_private_state obj;
> +        void *binding_user;
> +        ...
> +    }
> +
> +    struct komeda_pipeline_state {
> +        struct drm_private_state obj;
> +        struct drm_crtc *crtc;
> +        ...
> +    }
> +
> +komeda component validation
> +---------------------------
> +
> +Komeda has multiple types of components, but the process of validation are
> +similar, usually including the following steps:
> +
> +.. code-block:: c
> +
> +    int komeda_xxxx_validate(struct komeda_component_xxx xxx_comp,
> +                struct komeda_component_output *input_dflow,
> +                struct drm_plane/crtc/connector *user,
> +                struct drm_plane/crtc/connector_state, *user_state)
> +    {
> +         setup 1: check if component is needed, like the scaler is optional depending
> +                  on the user_state; if unneeded, just return, and the caller will
> +                  put the data flow into next stage.
> +         Setup 2: check user_state with component features and capabilities to see
> +                  if requirements can be met; if not, return fail.
> +         Setup 3: get component_state from drm_atomic_state, and try set to set
> +                  user to component; fail if component has been assigned to another
> +                  user already.
> +         Setup 3: configure the component_state, like set its input component,
> +                  convert user_state to component specific state.
> +         Setup 4: adjust the input_dflow and prepare it for the next stage.
> +    }
> +
> +komeda_kms Abstraction
> +----------------------
> +
> +.. kernel-doc:: drivers/gpu/drm/arm/display/komeda/komeda_kms.h
> +   :internal:
> +
> +komde_kms Functions
> +-------------------
> +.. kernel-doc:: drivers/gpu/drm/arm/display/komeda/komeda_crtc.c
> +   :internal:
> +.. kernel-doc:: drivers/gpu/drm/arm/display/komeda/komeda_plane.c
> +   :internal:
> +
> +Build komeda to be a Linux module driver
> +========================================
> +
> +Now we have two level devices:
> +
> +-   komeda_dev: describes the real display hardware.
> +-   komeda_kms_dev: attachs or connects komeda_dev to DRM-KMS.
> +
> +All komeda operations are supplied or operated by komeda_dev or komeda_kms_dev,
> +the module driver is only a simple wrapper to pass the Linux command
> +(probe/remove/pm) into komeda_dev or komeda_kms_dev.
> -- 
> 2.17.1
> 

-- 
====================
| I would like to |
| fix the world,  |
| but they're not |
| giving me the   |
 \ source code!  /
  ---------------
    Â\_(ã)_/Â