RFC Add pardata bus + tinydrm driver

This is an RFC - to get some responses on the overall design. The code builds but has not yet been tested on any HW. Before investing more time into this I would like some feedback if this is the right way forward or a different design should be pursued.

The problem to solve is that I have a propriatary ARM based board with a display that is connected using a parallel bus. The display is capable of showing graphics
so it is more advanced than what is found in auxdisplay/ I know there are others using a display connected
usign a parallel data bus, so this is not a unique problem for my board alone. But I do not expect many users as any modern design likely uses SPI or similar.

The old (proprietary) approach was to implement a char driver and then let some 3rd party lib use the char driver to write to the display.
The goal is to move to a more modern world where I expect to have a simple Qt based program running that can
be used for a few simple things.
(I do not expect any high performance and do not need it).

Implementation:

A pardata bus is implemented.
It uses a platform_driver to hook into the DT. When probed the pardatabus driver creates pardata devices for all child nodes in the tree.

Within tinydrm the pardata support is used to implement a driver for the display I have (Winstar wg160160). A library module is used to implement the more basic things allowing us to have a more simple driver, and thus making it simpler to add new drivers.

The implmentation uses array support in gpiolib to try to have some performance on screen updates.

TODO:
- Test on HW
- Add locking so there can be more than one user on the bus
- Improve pardata.rst documentation
- Add support for a sparkfun parallel data display (To verify that the library is generic)
- I may add a class if I see the need
- Likewise I may add sysfs attributes if there is a need for it

Any comments appreciated!

Sam

Sam Ravnborg (5):
dt-bindings: add parallel data bus (pardata)
pardata: new bus for parallel data access
tinydrm: add support for parallel data displays
dt-bindings: add winstar,wg160160 display bindings
tinydrm: add winstar wg160160 driver

 .../bindings/display/winstar,wg160160.txt          |  53 +++
 .../bindings/pardata/parallel-data-bus.txt         |  60 +++
 Documentation/driver-api/index.rst                 |   1 +
 Documentation/driver-api/pardata.rst               |  60 +++
 MAINTAINERS                                        |  14 +
 drivers/Kconfig                                    |   2 +
 drivers/Makefile                                   |   1 +
 drivers/gpu/drm/tinydrm/Kconfig                    |  13 +
 drivers/gpu/drm/tinydrm/Makefile                   |   2 +
 drivers/gpu/drm/tinydrm/pardata-dbi.c              | 417 +++++++++++++++++++++
 drivers/gpu/drm/tinydrm/wg160160.c                 | 298 +++++++++++++++
 drivers/pardata/Kconfig                            |  17 +
 drivers/pardata/Makefile                           |   5 +
 drivers/pardata/pardata.c                          | 282 ++++++++++++++
 include/drm/tinydrm/pardata-dbi.h                  | 257 +++++++++++++
 include/linux/pardata.h                            | 138 +++++++
 16 files changed, 1620 insertions(+)