Have this currently, although needs work and some decisions made about safety vs flexibility:
```rust
pub struct DmaWriteBuf<'a, T> {
     pub buf: &'a mut [T], // pub channel: DmaChannel,
}

unsafe impl<'a, T> WriteBuffer for DmaWriteBuf<'a, T> {
    type Word = T;

    unsafe fn write_buffer(&mut self) -> (*mut Self::Word, usize) {
        (self.buf.as_mut_ptr(), self.buf.len())
    }
}

impl<T> Drop for DmaWriteBuf<'_, T> {
    // todo: Hardcoded for DMA1 and Chan 3.
    // todo: Does this stop all transfers in progress?
    fn drop(&mut self) {
        unsafe {
            cfg_if! {
                if #[cfg(feature = "g4")] {
                    (*pac::DMA1::ptr()).ifcr.write(|w| w.gif2().clear_bit());
                } else if #[cfg(feature = "g0")] {
                } else if #[cfg(feature = "g0")] {
                    (*pac::DMA::ptr()).ifcr.write(|w| w.cgif2().clear_bit());
                } else {
                    (*pac::DMA1::ptr()).ifcr.write(|w| w.cgif2().clear_bit());
                }
            }
            cfg_if! {
                if #[cfg(feature = "f3")] {
                    (*pac::DMA1::ptr()).ch2.cr.modify(|_, w| w.en().clear_bit());
                } else if #[cfg(feature = "g0")] {
                    (*pac::DMA::ptr()).ch2.cr.modify(|_, w| w.en().clear_bit());
                } else {
                    (*pac::DMA1::ptr()).ccr2.modify(|_, w| w.en().clear_bit());
                }
            }
        }
    }
}