Introduction to CDF (V2)

Limitations of Existing Display Subsystem

CDF(v2) Internals

CDF(v2) Architecture

Exynos5250 MIPI DSI Driver prototyping using

CDF

LAURENT PINCHART proposed that display panel implementation based

on platform code based callbacks would need to be replaced by a driver-based

panel framework.

Several driver-based panel support solution already exist in the kernel.

- The LCD device class is implemented in drivers/video/backlight/lcd.c and

exposes a kernel API in include/linux/lcd.h. That API is tied to the FBDEV

API for historical reason, uses platform code callback for reset and power

management, and doesn't include support for standard features available

in today's "smart panels".

- OMAP2+ based systems use custom panel drivers available in

drivers/video/omap2/displays. Those drivers are based on OMAP DSS

(display controller) specific APIs.

- Similarly, Exynos based systems use custom panel drivers available in

drivers/video/exynos. single driver (s6e8ax0) is currently available. That

driver is based on Exynos display controller specific APIs and on the

LCD device class API.

There is no provision of supporting panels which support multiple

resolutions

Tied up with FBDEV framework

No generic methods for HOT Plug/Unplug.

No generic methods exposed to other driver (like

DRM/FBDEV/V4L2)

Display entity represents any hardware block that processes or sinks display-

related video streams.

Display entities are abstract object that must be implemented by a real device.

When a display entity driver probes a device it must create an

Instance of the display_entity structure,

Initialize it and

Register it with the CDF core.

The display entity exposes abstract operations through

function pointers, and the entity driver must implement those operations.

They are divided in 2 groups

Control operations

Video operations.

Control operations are called by upper-level drivers, usually in response to a

request originating from userspace.

They control the Display Entity State and Operation.

Currently defined control operations are

set_state(), to control the state of the entity (off, standby or on)

get_modes(), to retrieve the video modes supported by the entity

get_params(), to retrive the data bus parameters at the entity input (sink)

get_size(), to retrive the entity physical size (applicable to panels only)

Video operations are called by downstream entities on upstream entities

(from a video data bus point of view) to control the video operation.

The only currently defined video operation is

set_stream(), to start (in continuous or single-shot mode) the video stream

Video source entity pumps video data to the

display entities.

It has display interface specific operation like

Enabling the video source

Disabling

Read/Write cmds to Display Entity

Panel Driver

FBDEV DRM

DSI

DBI DPI HDMI/DVI

Panel driver Registration with I/F driver

• Power on

• Reset

• Backlight on/off

Display I/F drivers

Panel Driver

FBDEV DRM

DSI

DBI DPI HDMI/DVI CDF

Display I/F drivers

Video Source

registration

Display

Entity

Registration

MIPI DSI

Framework

LCD Panel

Driver

Registers driver with Exynos MIPI framework

In machine init LCD Panel

Device is registered with

Exynos MIPI Framework

MIPI DSI

Driver -

probe

Find matching driver for

LCD panel registered

during machine init,

attach the control ops to

the panel data structure

Call the probe of the LCD

panel driver Power on LCD panel

Call the init sequence of

the LCD panel using the

control ops

LCD Panel

Ready

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6

LCD driver registers with MIPI DSI framework, MIPI driver probe gets called and

it will in turn

Binds the LCD device with MIPI DSI Device

Calls the probe of the LCD driver

Puts the LCD on

And sets the initial sequence

MIPI DSI

Platform

Driver

LCD Panel

Platform

Driver

Power on LCD

panel

Return video

source and ops

LCD Panel

Ready

Common

Display

Framework Registers the “Video Source along

with control ops” with CDF

Find “video source”

by name.

Call the init

sequence of the

LCD panel using

video source ops

Registers the “Display

Entity” with CDF

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6

5

4

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MIPI DSI registers a “video source” with control ops with Common

Display Framework

Display Panel registers a “Display Entity” with control ops with

Common Display Framework

So during the probe of the PANEL driver, it finds its video source by

name, and uses the video source’s control ops to initialise the LCD

panel

http://www.mail-archive.com/dri-

devel@lists.freedesktop.org/msg35053.html

http://lwn.net/Articles/512363/

http://lwn.net/Articles/526965/

THANK YOU