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thunderbolt: Clamp DMA tunnel credits to what a hop register can hold

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struct tb_regs_hop::initial_credits is 7 bits wide, but neither of the
values tb_tunnel_alloc_dma() picks from is bounded by that: the
dma_credits module parameter has no upper limit, and neither does the
host router's baMaxHI. A larger count survives until tb_path_activate()
copies it into the register and keeps the low bits, leaving the path on
a credit count nobody asked for.

Clamp it in tb_tunnel_alloc_dma(), the only entry point for DMA tunnels;
every step below it can only lower the value further. Carry the count in
an unsigned int while at it.

Assisted-by: Claude:claude-opus-5
Signed-off-by: Fan Ye <fy15309206903@gmail.com>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
This commit is contained in:
Fan Ye
2026-08-11 05:57:59 +02:00
committed by Mika Westerberg
parent e8158c8a6a
commit 86feaba911
1 changed files with 9 additions and 1 deletions
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drivers/thunderbolt/tunnel.c
+9 -1
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@@ -48,6 +48,9 @@
#define TB_DP_AUX_PRIORITY 2
#define TB_DP_AUX_WEIGHT 1
/* struct tb_regs_hop::initial_credits is 7 bits wide */
#define TB_MAX_CREDITS 127
/* Minimum number of credits needed for PCIe path */
#define TB_MIN_PCIE_CREDITS 6U
/*
@@ -1907,7 +1910,7 @@ struct tb_tunnel *tb_tunnel_alloc_dma(struct tb *tb, struct tb_port *nhi,
struct tb_tunnel *tunnel;
size_t npaths = 0, i = 0;
struct tb_path *path;
int credits;
unsigned int credits;
/* Ring 0 is reserved for control channel */
if (WARN_ON(!receive_ring || !transmit_ring))
@@ -1930,6 +1933,11 @@ struct tb_tunnel *tb_tunnel_alloc_dma(struct tb *tb, struct tb_port *nhi,
tunnel->destroy = tb_dma_destroy;
credits = min_not_zero(dma_credits, nhi->sw->max_dma_credits);
if (credits > TB_MAX_CREDITS) {
tb_tunnel_dbg(tunnel, "%u credits do not fit a hop, using %u\n",
credits, TB_MAX_CREDITS);
credits = TB_MAX_CREDITS;
}
if (receive_ring > 0) {
path = tb_path_alloc(tb, dst, receive_path, nhi, receive_ring, 0,