Hey,

I was trying to do a FFT plan for a CuArray. The following works:

```
julia> using CUDA, CUDA.CUFFT
julia> x = CUDA.rand(2, 2)
2×2 CuArray{Float32, 2}:
0.318697 0.144699
0.631969 0.433798
julia> fft(x)
2×2 CuArray{ComplexF32, 2}:
1.52916+0.0im 0.37217+0.0im
-0.60237+0.0im -0.0241727+0.0im
julia> p = plan_fft(x);
julia> p * x
2×2 CuArray{ComplexF32, 2}:
1.52916+0.0im 0.37217+0.0im
-0.60237+0.0im -0.0241727+0.0im
```

Unfortunately I cannot get planning with a extra flag working:

```
help?> plan_fft
search: plan_fft plan_fft! plan_rfft plan_ifft plan_bfft plan_ifft! plan_bfft! plan_irfft plan_brfft
plan_fft(A [, dims]; flags=FFTW.ESTIMATE, timelimit=Inf)
[...]
julia> p = plan_fft(x, flags=FFTW.ESTIMATE);
ERROR: UndefVarError: FFTW not defined
Stacktrace:
[1] top-level scope
@ REPL[10]:1
```

Which makes sense since FFTW is not loaded. But the following is also clear to cause troubles since FFTW is not connected to CUDA (is it?). So the help is quite misleading.

```
julia> using FFTW
julia> p = plan_fft(x, flags=FFTW.ESTIMATE);
julia> p * x
ERROR: MethodError: *(::FFTW.cFFTWPlan{ComplexF32, -1, false, 2, UnitRange{Int64}}, ::CuArray{ComplexF32, 2}) is ambiguous. Candidates:
*(p::AbstractFFTs.Plan{T}, x::CuArray) where T in CUDA.CUFFT at /home/fxw/.julia/packages/CUDA/UC5gt/lib/cufft/fft.jl:11
*(p::FFTW.cFFTWPlan{T, K, false, N, G} where G where N, x::StridedArray{T, N}) where {T, K, N} in FFTW at /home/fxw/.julia/packages/FFTW/G3lSO/src/fft.jl:714
Possible fix, define
*(::FFTW.cFFTWPlan{T, K, false, N, G} where G where N, ::CuArray{T, N}) where {T, K, N}
Stacktrace:
[1] *(p::FFTW.cFFTWPlan{ComplexF32, -1, false, 2, UnitRange{Int64}}, x::CuArray{Float32, 2})
@ CUDA.CUFFT ~/.julia/packages/CUDA/UC5gt/lib/cufft/fft.jl:11
[2] top-level scope
@ REPL[13]:1
```

I tried to find something about the flags for CUFFT but couldn’t find something useful

So can anybody point me in the right direction?

Thanks,

Felix