add the support for displays without a RST pin

[pyaillet]

The choice was made here to rely on an internal NoPin implementation to hide the details
and expose it as an Alias type.

Proposal fix for #3

It would be used like this :

let display = DisplayNoRST::st7789_without_rst(di);

And it would be defined as:

  pub struct Twatch<'a> {
      pmu: Pmu<'a>,
      display: DisplayNoRST<EspSpi2InterfaceNoCS, mipidsi::models::ST7789>,
      [...]
  }

[almindor]

Do we need another type tho? I'm thinking making rst: Option<RST> with the additional no_rst contstructor variants will be less confusing.

[almindor]

It'll also force model implementors to account for this, which atm. the ST7789 doesn't for example (if it works it works by accident. I think I should do a soft reset in that case).

[pyaillet]

Do you mean the NoPin type or the DisplayNoRST type ?

1. I am using a custom NoPin type to avoid users to choose a random Pin when they mean to pass a None value for the RST Pin.
2. I am defining a DisplayNoRST type to avoid leaking the NoPin type externally

I don't know how it would be possible to use Option without needing to provide a specific Pin as a driver user, but any suggestion is welcome.

[almindor]

I mean 2.

Leaking NoPin is inevitable in this case, but at least the user won't really care, they just do Display::st7789_no_rst(di) or such and that's it from their perspective.

[pyaillet]

I tried to rewrite according to your remarks.

However you will see in the commit 48ed7ca that I took the init sequence from your old driver, as it solved the problem with the inverted colors for my TTGO T-Watch-2020.

[almindor]

Great job! thanks. Just a few nits + let's keep the init code change into a separate PR so we don't mix things too much.

[almindor]

could you add a basic documentation point here? just explain it's a dummy for the no-cs case.

[almindor]

let's keep this to a separate PR so we don't mix logical changes together.

[pyaillet]

Many thanks for the review :)

I removed the init seq from this PR and most of the comments shoulds be resolved now.

[almindor]

Thanks, this is great! I'll make a release after we get the init code in and tested out.