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(+)