[PATCH v4] thunderbolt: fix bandwidth group reservation indexing

[PATCH v4] thunderbolt: fix bandwidth group reservation indexing

[raoxu]

From: Xu Rao <raoxu@uniontech.com>

Valid bandwidth group IDs range from 1 through MAX_GROUPS, while Group
ID 0 is reserved. tb_consumed_dp_bandwidth() uses the Group ID directly
to index its local group_reserved[] array.

The array currently has MAX_GROUPS entries, so its valid indices are 0
through MAX_GROUPS - 1. Group ID MAX_GROUPS therefore accesses one
element past the end, and the final group's reserved bandwidth is not
included when the array is summed.

Give group_reserved[] MAX_GROUPS + 1 entries so direct Group ID
indexing covers the reserved ID 0 and valid IDs 1 through MAX_GROUPS.

Fixes: 52a4490e89d7 ("thunderbolt: Reserve released DisplayPort bandwidth for a group for 10 seconds")
Cc: stable@vger.kernel.org
Signed-off-by: Xu Rao <raoxu@uniontech.com>
---
Changes in v4:
- Keep MAX_GROUPS and the existing tb_cm::groups allocation, indexing,
  and iteration unchanged.
- Expand only group_reserved[] by one entry.
- Drop the bandwidth group remapping and loop changes from v3.

Changes in v3:
- Keep tb_cm::groups[] sized with MAX_GROUPS and map its entries
  directly to Group IDs 0 through 7.
- Initialize the reserved Group ID 0 entry, but skip it when allocating
  or discovering usable bandwidth groups.
- Drop the incorrect MAX_GROUPS - 1 sizing from v2.

Changes in v2:
- Keep Group ID as the direct group_reserved[] index instead of
  converting it to a zero-based index as in v1.
- Include the reserved Group ID 0 in MAX_GROUPS.

 drivers/thunderbolt/tb.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/thunderbolt/tb.c b/drivers/thunderbolt/tb.c
index b7cc689..47753a5 100644
--- a/drivers/thunderbolt/tb.c
+++ b/drivers/thunderbolt/tb.c
@@ -609,7 +609,7 @@ static int tb_consumed_dp_bandwidth(struct tb *tb,
 				    int *consumed_up,
 				    int *consumed_down)
 {
-	int group_reserved[MAX_GROUPS] = {};
+	int group_reserved[MAX_GROUPS + 1] = {};
 	struct tb_cm *tcm = tb_priv(tb);
 	struct tb_tunnel *tunnel;
 	bool downstream;
--
2.50.1

Re: [PATCH v4] thunderbolt: fix bandwidth group reservation indexing

[Mika Westerberg]

On Wed, Jun 24, 2026 at 02:27:03PM +0800, raoxu wrote:
> From: Xu Rao <raoxu@uniontech.com>
> 
> Valid bandwidth group IDs range from 1 through MAX_GROUPS, while Group
> ID 0 is reserved. tb_consumed_dp_bandwidth() uses the Group ID directly
> to index its local group_reserved[] array.
> 
> The array currently has MAX_GROUPS entries, so its valid indices are 0
> through MAX_GROUPS - 1. Group ID MAX_GROUPS therefore accesses one
> element past the end, and the final group's reserved bandwidth is not
> included when the array is summed.
> 
> Give group_reserved[] MAX_GROUPS + 1 entries so direct Group ID
> indexing covers the reserved ID 0 and valid IDs 1 through MAX_GROUPS.
> 
> Fixes: 52a4490e89d7 ("thunderbolt: Reserve released DisplayPort bandwidth for a group for 10 seconds")
> Cc: stable@vger.kernel.org
> Signed-off-by: Xu Rao <raoxu@uniontech.com>

Applied to thunderbolt.git/fixes, thanks!