Revert "drm/bridge: ti-sn65dsi83: Fix enable error path"

[ Upstream commit ad81feb ]

This reverts commit 8a91b29.

The regulator_disable() added by the original commit solves one kind of
regulator imbalance but adds another one as it allows the regulator to be
disabled one more time than it is enabled in the following scenario:

 1. Start video pipeline -> sn65dsi83_atomic_pre_enable -> regulator_enable
 2. PLL lock fails -> regulator_disable
 3. Stop video pipeline -> sn65dsi83_atomic_disable -> regulator_disable

The reason is clear from the code flow, which looks like this (after
removing unrelated code):

  static void sn65dsi83_atomic_pre_enable()
  {
      regulator_enable(ctx->vcc);

      if (PLL failed locking) {
          regulator_disable(ctx->vcc);  <---- added by patch being reverted
          return;
      }
  }

  static void sn65dsi83_atomic_disable()
  {
      regulator_disable(ctx->vcc);
  }

The use case for introducing the additional regulator_disable() was
removing the module for debugging (see link below for the discussion). If
the module is removed after a .atomic_pre_enable, i.e. with an active
pipeline from the DRM point of view, .atomic_disable is not called and thus
the regulator would not be disabled.

According to the discussion however there is no actual use case for
removing the module with an active pipeline, except for
debugging/development.

On the other hand, the occurrence of a PLL lock failure is possible due to
any physical reason (e.g. a temporary hardware failure for electrical
reasons) so handling it gracefully should be supported. As there is no way
for .atomic[_pre]_enable to report an error to the core, the only clean way
to support it is calling regulator_disabled() only in .atomic_disable,
unconditionally, as it was before.

Link: https://lore.kernel.org/all/15244220.uLZWGnKmhe@steina-w/
Fixes: 8a91b29 ("drm/bridge: ti-sn65dsi83: Fix enable error path")
Reviewed-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Signed-off-by: Robert Foss <rfoss@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240426122259.46808-1-luca.ceresoli@bootlin.com
(cherry picked from commit 2940ee0)
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

drivers/gpu/drm/bridge/ti-sn65dsi83.c

@@ -478,7 +478,6 @@ static void sn65dsi83_atomic_pre_enable(struct drm_bridge *bridge,
 		dev_err(ctx->dev, "failed to lock PLL, ret=%i\n", ret);
 		/* On failure, disable PLL again and exit. */
 		regmap_write(ctx->regmap, REG_RC_PLL_EN, 0x00);
-		regulator_disable(ctx->vcc);
 		return;
 	}