[iMXRT] dma: fix transfer count computation

count should be defined as the integer div_round_up of buffer length
and word size, otherwise transferring small buffers will cause a panic
due to underflow:

if we let from = [0u32; 1];

then calling dma::write() will result in:

let count = ((1 / 4 as usize) - 1)
          = 0 - 1 // underflow

Rounding up results in 1 - 1 as expected.

1 files changed, 3 insertions, 3 deletions

diff --git a/embassy-imxrt/src/dma.rs b/embassy-imxrt/src/dma.rs
index 76c9953c1..eaa09870d 100644
--- a/embassy-imxrt/src/dma.rs
+++ b/embassy-imxrt/src/dma.rs
@@ -71,7 +71,7 @@ pub(crate) unsafe fn init() {
 ///
 /// SAFETY: Slice must point to a valid location reachable by DMA.
 pub unsafe fn read<'a, C: Channel, W: Word>(ch: Peri<'a, C>, from: *const W, to: *mut [W]) -> Transfer<'a, C> {
-    let count = ((to.len() / W::size() as usize) - 1) as isize;
+    let count = (to.len().div_ceil(W::size() as usize) - 1) as isize;
 
     copy_inner(
         ch,
@@ -89,7 +89,7 @@ pub unsafe fn read<'a, C: Channel, W: Word>(ch: Peri<'a, C>, from: *const W, to:
 ///
 /// SAFETY: Slice must point to a valid location reachable by DMA.
 pub unsafe fn write<'a, C: Channel, W: Word>(ch: Peri<'a, C>, from: *const [W], to: *mut W) -> Transfer<'a, C> {
-    let count = ((from.len() / W::size() as usize) - 1) as isize;
+    let count = (from.len().div_ceil(W::size() as usize) - 1) as isize;
 
     copy_inner(
         ch,
@@ -111,7 +111,7 @@ pub unsafe fn copy<'a, C: Channel, W: Word>(ch: Peri<'a, C>, from: &[W], to: &mu
     let to_len = to.len();
     assert_eq!(from_len, to_len);
 
-    let count = ((from_len / W::size() as usize) - 1) as isize;
+    let count = (from_len.div_ceil(W::size() as usize) - 1) as isize;
 
     copy_inner(
         ch,