[PATCH v2 2/3] thunderbolt: Fix DMA credit limit to use host router value

[Gil Fine <gil.fine@linux.intel.com>]

Currently, when allocating credits for a DMA tunnel, we reserve credits
based on the baMaxHI parameter taken from the router that owns the
ingress adapter of the current hop.
In a host-to-host topology with a hub in the middle:

  [Host1] <-> [Hub] <-> [Host2]

this incorrectly uses the hub's value instead of the host router's.
The DMA engine limit is defined by the host router baMaxHI.

Fix this by alway use the baMaxHI of the host router instead.

Fixes: 6ed541c53edc ("thunderbolt: Allocate credits according to router preferences")
Cc: stable@vger.kernel.org
Signed-off-by: Gil Fine <gil.fine@linux.intel.com>
Assisted-by: LLM
---
 drivers/thunderbolt/tunnel.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/thunderbolt/tunnel.c b/drivers/thunderbolt/tunnel.c
index 7a033df7f916..0625b1ff3820 100644
--- a/drivers/thunderbolt/tunnel.c
+++ b/drivers/thunderbolt/tunnel.c
@@ -175,7 +175,8 @@ static unsigned int tb_available_credits(const struct tb_port *port,
 	pcie = tb_acpi_may_tunnel_pcie() ? sw->max_pcie_credits : 0;
 
 	if (tb_acpi_is_xdomain_allowed()) {
-		spare = min_not_zero(sw->max_dma_credits, dma_credits);
+		spare = min_not_zero(sw->tb->root_switch->max_dma_credits,
+				     dma_credits);
 		/* Add some credits for potential second DMA tunnel */
 		spare += TB_MIN_DMA_CREDITS;
 	} else {
-- 
2.43.0