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drm/amd/display: fix division by zero in get_estimated_bw()

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get_estimated_bw() divides by link->dpia_bw_alloc_config.bw_granularity,
which is zeroed by reset_bw_alloc_struct() and only populated once
DP_TUNNELING_BW_ALLOC_CAP_CHANGED has been handled.

link_dp_dpia_handle_bw_alloc_status(), the DPCD interrupt handler,
calls get_estimated_bw() whenever DP_TUNNELING_ESTIMATED_BW_CHANGED
is set, independently of whether DP_TUNNELING_BW_ALLOC_CAP_CHANGED
has ever fired for that link. A connected USB4/DPIA tunneling device
that reports an estimated-bandwidth change before ever reporting a
capability change drives a division by zero in this IRQ path.

link_dpia_send_bw_alloc_request() already guards the same
bw_granularity division; add the identical guard here rather than
introducing a new pattern.

Fixes: 8e5cfe547b ("drm/amd/display: upstream link_dp_dpia_bw.c")
Reviewed-by: Alex Hung <alex.hung@amd.com>
Assisted-by: gkh_clanker_t1000
Signed-off-by: Hari Mishal <harimishal1@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit f2a961457c33dc34223aad5c9e8971de34a4eed3)
Cc: stable@vger.kernel.org
This commit is contained in:
Hari Mishal 2026-08-22 16:57:51 +02:00 committed by Alex Deucher
parent 4278d65a41
commit f63de9054d
1 changed files with 5 additions and 0 deletions
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5
drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_dpia_bw.c
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@ -103,6 +103,11 @@ static int get_estimated_bw(struct dc_link *link)
{
uint8_t bw_estimated_bw = 0;
if (link->dpia_bw_alloc_config.bw_granularity == 0) {
DC_LOG_ERROR("%s: BW granularity is zero!\n", __func__);
return 0;
}
core_link_read_dpcd(
link,
ESTIMATED_BW,