[PATCH] drm/tegra: Fix regulator_get_optional() misuse

[Thierry Reding]

On Tue, Nov 05, 2019 at 12:59:42PM +0000, Mark Brown wrote:
> The tegra driver requests a supply using regulator_get_optional()
> but both the name of the supply and the usage pattern suggest that it is
> being used for the main power for the device and is not at all optional
> for the device for function, there is no meaningful handling for absent
> supplies.  Such regulators should use the vanilla regulator_get()
> interface, it will ensure that even if a supply is not described in the
> system integration one will be provided in software.
> 
> Signed-off-by: Mark Brown <broonie at kernel.org>
> ---
>  drivers/gpu/drm/tegra/dpaux.c | 32 ++++++++++++--------------------
>  1 file changed, 12 insertions(+), 20 deletions(-)

It is in fact optional in this case. This code remains solely for
backwards compatibility with old DTBs because back at the time the VDD
supply was associated with the DPAUX block where it should've really
been associated with the eDP panel.

See also this commit for some background:

commit f3b0d8793c1619074d0ece2e1a7f64ea37eaf394
Author: Thierry Reding <treding at nvidia.com>
Date:   Wed Jun 5 10:48:01 2019 +0200

    drm/tegra: dpaux: Make VDD supply optional

    The VDD supply is only needed to supply power to eDP panels connected to
    DPAUX. Technically that supply should be dealt with in the panel driver,
    but for backwards-compatibility we need to keep this around anyway.

    Also as a bit of background: the reason for why this supply is attached
    to DPAUX is to make sure the panel is properly powered early on so that
    it can generate a hotplug pulse at the appropriate time. This may no
    longer be required given the support for deferred fbdev setup that was
    "recently" introduced in DRM/KMS.

    Signed-off-by: Thierry Reding <treding at nvidia.com>

Thierry
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