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

[Noralf Trønnes]

Den 18.02.2020 21.57, skrev Andy Shevchenko:
> On Sun, Feb 16, 2020 at 7:30 PM Noralf Trønnes <noralf at tronnes.org> 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
> 
> Can regmap-usb be used for drivers/mfd/dln2.c for example?
> 

No, apparently dln-2 uses custom protocol structs for each function with
a common header. regmap-usb is a register abstraction with the ability
to bulk read/write multiple registers in one transfer.

I see that dln-2 does a lot of what I'm aiming for except that it
doesn't have the display part.

Noralf.