Photoshop: Using level layers to adjust a mask

Question

I need to use leveling layers to adjust the gradients of my layer mask. However, Photoshop doesn't support that. I tried using a clipping mask, but a clipping mask uses the alpha channel, not the brightness of the pixels to mask. So this doesn't help me either, because leveling layers cannot be applied to the alpha channel. How do I do this?

Edit: A quick example

In the upper half I have an image (here the Dragon Ball logo) and a layer mask (here just a simple gradient).
However, in my actual use case, I need the result to blend into the rest of the image perfectly. That means I need to fine tune the layer mask.
So in the lower half, I created a group with the gradient and a leveling layer to tune it. Now, I could collapse the group to a single layer and use it as a mask for the (logo). But then I would lose the ability to fine-tune. The environment it needs to blend in might change and I will be unable to readjust. I also don't really get a preview of how my (logo) will look like with these settings.

Answer 1

Sorry I'm late to the party but we can do this while maintaining control.

1. Create a Black to White Gradient.
2. Layer → Layer Style → Blending Options
3. Hold Alt and separate the black slider and pull the right side of it all the way to the right:

4. Now create a Levels Adjustment on top of this.
5. Now group these two together
6. Put your image on the top of the group and clip it to the entire group
7. Adjust the level, and presto -- you're adjusting the mask.

Granted I have no idea why you wouldn't just use the blending options to begin with, but here's a work-around for you anyways to do what you'd like.

Answer 2

Edit: For a working method follow Ryan's answer.
The following illustrates how this can/can't be done with actual layer masks.

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You can't use adjustment layers to directly effect a mask, but you can use regular adjustments.

Take this example with a simple gradient mask:

Alt+Click on the mask thumbnail to edit the mask. This will make only the mask channel visible. You can then use a normal adjustment (i.e Image → Adjustments → Levels or Curves or whatever else) to refine your mask:

Click on the layer thumbnail (not the mask thumbnail) to finish editing the mask:

A better option is to simply select the mask in the Channels panel. That will allow you to edit the mask with or without the other channels visible: