[RFC 0/9] Regmap over USB for Multifunction USB Device (gpio, display, ...)

[Daniel Vetter]

On Sun, Feb 16, 2020 at 06:21:08PM +0100, Noralf Trønnes wrote:
> Hi,
> 
> A while back I had the idea to turn a Raspberry Pi Zero into a $5
> USB to HDMI/SDTV/DSI/DPI display adapter.
> 
> Thinking about how to represent the display to the driver I realised
> that hardware use registers as API. And Linux does have a generic
> register abstraction: regmap. Furthermore this means that if I can do a
> regmap over USB implementation, it will be easy to do other functions
> like gpio, adc and others. After a few iterations trying to understand
> the USB subsystem and satisfying driver requirements, I now have
> something that looks promising.
> 
> I'm sending out an early version hoping to get feedback especially on
> the core parts that handles regmap and interrupts.
> 
> Overview:
> 
>           USB Host          :         USB Device
>                             :
>             --------------  :  ------------------
> ----------  | mfd: mud   |  :  | f_mud          |  ----------
> | Driver |  --------------  :  |                |  | Driver |
> ----------  | regmap-usb |  :  | (mud_regmap)   |  ----------
>             --------------  :  ------------------
> 
> 
> I've attached 2 drivers:
> - gpio/pinctrl: is more or less finished
> - display: needs a lot more work
> 
> 
> USB3 device
> I've only tested this with usb2 devices (Pi, BBB) so I should get myself
> a usb3 gadget capable board. My searching didn't turn up much, so this
> seems to be quite rare. ROCK960 has USB 3.0 type C OTG but the price is
> $139 which is a bit expensive for this hobby project. Does anyone know
> of a cheap board?
> 
> Noralf.

Pretty cool idea, and the drm side looks really tiny (after all your
drm_client work that is). I think the important feedback here is for the
usb and regmap stuff, that's totally out of my area. I've commented on the
drm_client patch, but that's just minor stuff, imo looks good.

Cheers, Daniel

> 
> 
> Noralf Trønnes (9):
>   regmap: Add USB support
>   mfd: Add driver for Multifunction USB Device
>   usb: gadget: function: Add Multifunction USB Device support
>   pinctrl: Add Multifunction USB Device pinctrl driver
>   usb: gadget: function: mud: Add gpio support
>   regmap: Speed up _regmap_raw_write_impl() for large buffers
>   drm: Add Multifunction USB Device display driver
>   drm/client: Add drm_client_init_from_id() and drm_client_modeset_set()
>   usb: gadget: function: mud: Add display support
> 
>  drivers/base/regmap/Kconfig              |    8 +-
>  drivers/base/regmap/Makefile             |    1 +
>  drivers/base/regmap/regmap-usb.c         | 1026 ++++++++++++++++++
>  drivers/base/regmap/regmap.c             |   10 +-
>  drivers/gpu/drm/Kconfig                  |    2 +
>  drivers/gpu/drm/Makefile                 |    1 +
>  drivers/gpu/drm/drm_client.c             |   37 +
>  drivers/gpu/drm/drm_client_modeset.c     |   52 +
>  drivers/gpu/drm/mud/Kconfig              |   18 +
>  drivers/gpu/drm/mud/Makefile             |    4 +
>  drivers/gpu/drm/mud/mud_drm.c            | 1198 ++++++++++++++++++++++
>  drivers/gpu/drm/mud/mud_drm.h            |  137 +++
>  drivers/gpu/drm/mud/mud_drm_gadget.c     |  889 ++++++++++++++++
>  drivers/mfd/Kconfig                      |    8 +
>  drivers/mfd/Makefile                     |    1 +
>  drivers/mfd/mud.c                        |  580 +++++++++++
>  drivers/pinctrl/Kconfig                  |    9 +
>  drivers/pinctrl/Makefile                 |    1 +
>  drivers/pinctrl/pinctrl-mud.c            |  657 ++++++++++++
>  drivers/pinctrl/pinctrl-mud.h            |   89 ++
>  drivers/usb/gadget/Kconfig               |   36 +
>  drivers/usb/gadget/function/Makefile     |    6 +
>  drivers/usb/gadget/function/f_mud.c      |  913 +++++++++++++++++
>  drivers/usb/gadget/function/f_mud.h      |  210 ++++
>  drivers/usb/gadget/function/f_mud_drm.c  |  181 ++++
>  drivers/usb/gadget/function/f_mud_pins.c |  962 +++++++++++++++++
>  drivers/usb/gadget/function/mud_regmap.c |  936 +++++++++++++++++
>  include/drm/drm_client.h                 |    4 +
>  include/linux/mfd/mud.h                  |   16 +
>  include/linux/regmap.h                   |   23 +
>  include/linux/regmap_usb.h               |   97 ++
>  31 files changed, 8107 insertions(+), 5 deletions(-)
>  create mode 100644 drivers/base/regmap/regmap-usb.c
>  create mode 100644 drivers/gpu/drm/mud/Kconfig
>  create mode 100644 drivers/gpu/drm/mud/Makefile
>  create mode 100644 drivers/gpu/drm/mud/mud_drm.c
>  create mode 100644 drivers/gpu/drm/mud/mud_drm.h
>  create mode 100644 drivers/gpu/drm/mud/mud_drm_gadget.c
>  create mode 100644 drivers/mfd/mud.c
>  create mode 100644 drivers/pinctrl/pinctrl-mud.c
>  create mode 100644 drivers/pinctrl/pinctrl-mud.h
>  create mode 100644 drivers/usb/gadget/function/f_mud.c
>  create mode 100644 drivers/usb/gadget/function/f_mud.h
>  create mode 100644 drivers/usb/gadget/function/f_mud_drm.c
>  create mode 100644 drivers/usb/gadget/function/f_mud_pins.c
>  create mode 100644 drivers/usb/gadget/function/mud_regmap.c
>  create mode 100644 include/linux/mfd/mud.h
>  create mode 100644 include/linux/regmap_usb.h
> 
> -- 
> 2.23.0
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch