I can't get the VK_KHR_Display display count

Hi!

I am trying to add Vulkan support to SDL2 outside X, using the VK_KHR_Display extension.

I have this extension active, and as such I can retrieve the pointer to vkCreateDisplayPlaneSurfaceKHR(), using vkGetInstanceProcAddr() on the program’s instance.

However, when I try to get the display count using vkGetPhysicalDeviceDisplayPropertiesKHR(), I get 0 displays. Any idea on what am I doing wrong?

Here’s where I successfully retrieve the vkCreateDisplayPlaneSurfaceKHR() pointer:
https://github.com/vanfanel/SDL/blob/11e4911657edc495e196b9f262b0b523fe9ad8e0/src/video/kmsdrm/SDL_kmsdrmvulkan.c#L179

And here is where I try to retrieve the display count that results in 0 displays:
https://github.com/vanfanel/SDL/blob/11e4911657edc495e196b9f262b0b523fe9ad8e0/src/video/kmsdrm/SDL_kmsdrmvulkan.c#L276

I am trying this on AMDGPU and intel graphics with the same result.
Any idea on what am I doing wrong?