Revert copy to RAM in embedded hal spim transfer. The mut slice must already be in RAM, so no check neccessary

Author: Henrik Alsér

nrf-hal-common/,

@@ -41,24 +41,13 @@ where
     type Error = Error;
 
     fn transfer<'w>(&mut self, words: &'w mut [u8]) -> Result<&'w [u8], Error> {
-        if slice_in_ram(words) {
-            words.chunks(EASY_DMA_SIZE).try_for_each(|chunk| {
-                self.do_spi_dma_transfer(DmaSlice::from_slice(chunk), DmaSlice::from_slice(chunk))
-            })?;
-        } else {
-            words
-                .chunks_mut(FORCE_COPY_BUFFER_SIZE)
-                .try_for_each(|chunk| {
-                    let mut buf = [0u8; FORCE_COPY_BUFFER_SIZE];
-                    buf[..chunk.len()].copy_from_slice(chunk);
-                    self.do_spi_dma_transfer(
-                        DmaSlice::from_slice(&buf[..chunk.len()]),
-                        DmaSlice::from_slice(&buf[..chunk.len()]),
-                    )?;
-                    chunk.copy_from_slice(&buf[..chunk.len()]);
-                    Ok(())
-                })?;
-        }
+        // If the slice isn't in RAM, we can't write back to it at all
+        slice_in_ram_or(words, Error::DMABufferNotInDataMemory)?;
+
+        words.chunks(EASY_DMA_SIZE).try_for_each(|chunk| {
+            self.do_spi_dma_transfer(DmaSlice::from_slice(chunk), DmaSlice::from_slice(chunk))
+        })?;
+
         Ok(words)
     }
 }