epaper_spi: Busy pin validated as output instead of input?

[schdro]

Component name

epaper_spi

Link to component documentation on our website

https://esphome.io/components/display/epaper_spi/

Describe the enhancement

Found in current ESPHome 2025.12.5 while trying to develop new epaper_spi module:
https://github.com/esphome/esphome/blob/2025.12.5/esphome/components/epaper_spi/display.py#L90

model.option(pin): pins.gpio_output_pin_schema
for pin in (CONF_RESET_PIN, CONF_CS_PIN, CONF_BUSY_PIN)

Busy pin is validated as output. Also in generated C++ code (main.cpp), it is found as output.
But for epaper SPI protocol, busy is regularly input to the MCU.

Even doc of epaper_spi YAML examples sees busy as input:
https://esphome.io/components/display/epaper_spi/

Deprecated old component waveshare_epaper seemed to validate busy pin correctly as input schema:
https://github.com/esphome/esphome/blob/2025.12.5/esphome/components/waveshare_epaper/display.py#L210

Suggestion to change e.g. to:

model.option(CONF_BUSY_PIN): pins.gpio_input_pin_schema,
model.option(CONF_CS_PIN): pins.gpio_output_pin_schema,
model.option(CONF_RESET_PIN): pins.gpio_output_pin_schema,

(unrolled to also have freedom for per pin validations)

P.S. Debatable whether "Python breaking change".
But IMHO is does not break any documented Python or C++ public API, nor documentation:
https://esphome.io/components/display/epaper_spi/
Furthermore, fixing early avoids need to change later when epaper_spi gets wider deployed.

P.S. Did not want to include into another unrelated upcoming PR for supporting new EPD (requiring BUSY), as it is more general component fix/change. Maybe even desired as is?

Use cases

Use of epaper_spi for boards requiring BUSY input pin
(Spectra E6, new upcoming Waveshare 1.54 (G) board under prep)

Anything else?

No response

[github-actions[bot]]

🏷️ I've automatically added the component: epaper_spi label to help categorize this feature request.