Resource: LCA13 Name: Common Display Framework (CDF) Date: 05-03-2013 Speaker: Tom Gall

2.  Introduction to CDF (V2)
 Limitations of Existing Display Subsystem
 CDF(v2) Internals
 CDF(v2) Architecture
 Exynos5250 MIPI DSI Driver prototyping using
CDF

3. 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.

4.  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)

5. 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.

6. 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)

7. 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

8.  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

9. 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

10. Panel Driver
FBDEV DRM
DSI DBI DPI HDMI/DVI CDF
Display I/F drivers
Video Source
registration
Display
Entity
Registration

11. 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
1
2
3
4
5
6

12. 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

13. MIPI DSI
Platform
Driver
LCD Panel
Platform
Driver
Power on LCD
panel
Return video
source and ops
LCD Panel
Ready
Common
Display
FrameworkRegisters 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
2
6
5
4
31

14.  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

15.  http://www.mail-archive.com/dri-
devel@lists.freedesktop.org/msg35053.html
 http://lwn.net/Articles/512363/
 http://lwn.net/Articles/526965/

16. THANK YOU