Re: [PATCH 2/2] drm/i915/vlv_dsi: Control panel and backlight enable GPIOs on BYT

[Linus Walleij <linus.walleij@linaro.org>]

Hi Hans,

thank you for your patch!

On Fri, Nov 29, 2019 at 7:58 PM Hans de Goede <hdegoede@redhat.com> wrote:

> -       /* GPIO Desc for CRC based Panel control */
> +       /* GPIO Desc for panel and backlight control */
>         struct gpio_desc *gpio_panel;
> +       struct gpio_desc *gpio_backlight;

I think what happens here is that you reimplement
drivers/video/backlight/gpio_backlight.c

The existing power control GPIO also reimplements
drivers/regulator/fixed.c in a sense but I am under the
impression that x86 in general and ACPI in particular
has a problem with the regulator subsystem so I am
uncertain about that one.

When I look at the code I get more confused because
nominally panels should have their own drivers in
drivers/gpu/drm/panel/* especially DSI panels, and the
panels control their own GPIOs or regulators for power
and backlight.

I was under the impression that Heikki's and Dmitry's
recent additions to software nodes would make it
possible to actually spawn devices like the GPIO backlight
and/or fixed regulator and put references to them so
that the drivers can pick them up from the respective
frameworks and manage them?

Maybe I misunderstood things here though, I am a bit
under the impression that elder DRM drivers are
considered "elder gods" and do not need to use separate
panel drivers, backlight abstraction etc, and in that
case just go ahead, I guess.

But I suspect some separation
would help the day the i915 driver wants to reuse some
really complex DSI panel from drivers/gpu/drm/panel/*
though.

Yours,
Linus Walleij