The current code indexes into `after_rx` using `tx` which is an index
for the whole buffer, not the split buffer `after_rx`.
Also add more rigorous no-panic proofs.
Fixes: 75f6b1de8133 ("gpu: nova-core: gsp: Add GSP command queue bindings and
handling")
Signed-off-by: Eliot Courtney <[email protected]>
---
drivers/gpu/nova-core/gsp/cmdq.rs | 17 ++++++++++++-----
1 file changed, 12 insertions(+), 5 deletions(-)
diff --git a/drivers/gpu/nova-core/gsp/cmdq.rs
b/drivers/gpu/nova-core/gsp/cmdq.rs
index b6d6093e3ac0..5ca1d757d4a3 100644
--- a/drivers/gpu/nova-core/gsp/cmdq.rs
+++ b/drivers/gpu/nova-core/gsp/cmdq.rs
@@ -1,7 +1,6 @@
// SPDX-License-Identifier: GPL-2.0
use core::{
- cmp,
mem,
sync::atomic::{
fence,
@@ -265,10 +264,18 @@ fn new(dev: &device::Device<device::Bound>) ->
Result<Self> {
// PANIC: per the invariant of `cpu_read_ptr`, `rx` is `<
MSGQ_NUM_PAGES`.
let (before_rx, after_rx) = gsp_mem.gspq.msgq.data.split_at(rx);
- match tx.cmp(&rx) {
- cmp::Ordering::Equal => (&after_rx[0..0], &after_rx[0..0]),
- cmp::Ordering::Greater => (&after_rx[..tx], &before_rx[0..0]),
- cmp::Ordering::Less => (after_rx, &before_rx[..tx]),
+ // The area starting at `rx` and ending at `tx - 1` modulo
MSGQ_NUM_PAGES, inclusive,
+ // belongs to the driver for reading.
+ if rx <= tx {
+ // The area is contiguous.
+ // PANIC: since `rx <= tx` we have `tx - rx >= 0`
+ // PANIC: since `tx < MSGQ_NUM_PAGES && after_rx.len() ==
MSGQ_NUM_PAGES - rx`:
+ // `tx - rx <= MSGQ_NUM_PAGES - rx` -> `tx - rx <=
after_rx.len()`
+ (&after_rx[..(tx - rx)], &after_rx[0..0])
+ } else {
+ // The area is discontiguous.
+ // PANIC: since `tx < rx && before_rx.len() == rx` we have `tx <=
before_rx.len()`
+ (after_rx, &before_rx[..tx])
}
}
--
2.52.0
