drm/panel: s6e63m0: Make s6e63m0_remove() return void

Up to now s6e63m0_remove() returns zero unconditionally. Make it return
void instead which makes it easier to see in the callers that there is
no error to handle.

Also the return value of spi remove callbacks is ignored anyway.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20211011132754.2479853-2-u.kleine-koenig@pengutronix.de

drm/panel: s6e63m0: Switch to DBI abstraction for SPI

The SPI access to s6e63m0 is using the DBI protocol, so switch
to using the elaborate DBI protocol implementation in the DRM
DBI helper library.

Acked-by: Noralf Trønnes <noralf@tronnes.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20210614181135.1124445-2-linus.walleij@linaro.org

drm/panel: s6e63m0: Add reading functionality

This adds code to send read commands to read a single
byte from the display, in order to perform MTP ID
look-up of the mounted panel on the s6e63m0 controller.
This is needed for proper biasing on the DSI variants.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Tested-by: Stephan Gerhold <stephan@gerhold.net>
Cc: Paweł Chmiel <pawel.mikolaj.chmiel@gmail.com>
Acked-by: Paul Cercueil <paul@crapouillou.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20200809215104.1830206-4-linus.walleij@linaro.org

drm/panel: s6e63m0: Add DSI transport

This makes it possible to use the s6e63m0 panel with a
DSI host, such as in the Samsung GT-I8190 (Golden) mobile
phone.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Tested-by: Stephan Gerhold <stephan@gerhold.net>
Cc: Stephan Gerhold <stephan@gerhold.net>
Cc: Paweł Chmiel <pawel.mikolaj.chmiel@gmail.com>
Acked-by: Paul Cercueil <paul@crapouillou.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20200809215104.1830206-3-linus.walleij@linaro.org

drm/panel: s6e63m0: Break out SPI transport

This panel can be accessed using both SPI and DSI.

To make it possible to probe and use the device also from
a DSI bus, first break out the SPI support to its own file.

Since all the panel driver does is write DCS commands to
the panel, we pass a DCS write function to probe()
from each subdriver.

We make the Kconfig entry for SPI mode default so all
current users will continue to work.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Tested-by: Stephan Gerhold <stephan@gerhold.net>
Cc: Paweł Chmiel <pawel.mikolaj.chmiel@gmail.com>
Acked-by: Paul Cercueil <paul@crapouillou.net>
Link: https://patchwork.freedesktop.org/patch/384873/