[PATCH 2/2 v4] drm/panel: ws2401: Add driver for WideChips WS2401

[Doug Anderson]

Hi,

On Wed, Jul 14, 2021 at 3:52 PM Linus Walleij <linus.walleij at linaro.org> wrote:
>
> This adds a driver for panels based on the WideChips WS2401 display
> controller. This display controller is used in the Samsung LMS380KF01
> display found in the Samsung GT-I8160 (Codina) mobile phone and
> possibly others.
>
> As is common with Samsung displays manufacturer commands are necessary
> to configure the display to a working state.
>
> The display optionally supports internal backlight control, but can
> also use an external backlight.
>
> This driver re-uses the DBI infrastructure to communicate with the
> display.
>
> Cc: phone-devel at vger.kernel.org
> Cc: Douglas Anderson <dianders at chromium.org>
> Reviewed-by: Noralf Trønnes <noralf at tronnes.org>
> Reviewed-by: Douglas Anderson <dianders at chromium.org>
> Signed-off-by: Linus Walleij <linus.walleij at linaro.org>
> ---
> ChangeLog v3->v4:
> - Add more talkative Kconfig telling which mobile phone has this.
> - Make sure to turn off the internal backlight totally if requested.
> - Alter the logic so that we assign the backlight handle to
>   panel->backlight directly and save some code.

Officially this is disallowed according to comments. ...and I quote:

/**
 * @backlight:
 *
 * Backlight device, used to turn on backlight after the call
 * to enable(), and to turn off backlight before the call to
 * disable().
 * backlight is set by drm_panel_of_backlight() or
 * drm_panel_dp_aux_backlight() and drivers shall not assign it.
 */

I do not personally know the motivation of not letting drivers assign
it, but with the words "shall not". Yikes!

-Doug