drm/radeon: Fix PCIe lane width calculation

commit 85e290d92b4b794d0c758c53007eb4248d385386 upstream.

Two years ago I tried an AMD Radeon E8860 embedded GPU with the drm driver.
The dmesg output included driver warnings about an invalid PCIe lane width.
Tracking the problem back led to si_set_pcie_lane_width_in_smc().
The calculation of the lane widths via ATOM_PPLIB_PCIE_LINK_WIDTH_MASK and
ATOM_PPLIB_PCIE_LINK_WIDTH_SHIFT macros did not increment the resulting
value, per the comment in pptable.h ("lanes - 1"), and per usage elsewhere.
Applying the increment silenced the warnings.
The code has not changed since, so either my analysis was incorrect or the
bug has gone unnoticed. Hence submitting this as an RFC.

Acked-by: Christian König <christian.koenig@amd.com>
Acked-by: Chunming Zhou <david1.zhou@amd.com>
Signed-off-by: Paul Parsons <lost.distance@yahoo.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/gpu/drm/radeon/si_dpm.c b/drivers/gpu/drm/radeon/si_dpm.c
index 2113869e86784447bdcba5c9e7753248f93fc264..c8509c9992f1a57b9894e6afb9a4d860ddc22e98 100644 (file)
--- a/drivers/gpu/drm/radeon/si_dpm.c
+++ b/drivers/gpu/drm/radeon/si_dpm.c
@@ -5894,9 +5894,9 @@ static void si_set_pcie_lane_width_in_smc(struct radeon_device *rdev,
 {
        u32 lane_width;
        u32 new_lane_width =
-               (radeon_new_state->caps & ATOM_PPLIB_PCIE_LINK_WIDTH_MASK) >> ATOM_PPLIB_PCIE_LINK_WIDTH_SHIFT;
+               ((radeon_new_state->caps & ATOM_PPLIB_PCIE_LINK_WIDTH_MASK) >> ATOM_PPLIB_PCIE_LINK_WIDTH_SHIFT) + 1;
        u32 current_lane_width =
-               (radeon_current_state->caps & ATOM_PPLIB_PCIE_LINK_WIDTH_MASK) >> ATOM_PPLIB_PCIE_LINK_WIDTH_SHIFT;
+               ((radeon_current_state->caps & ATOM_PPLIB_PCIE_LINK_WIDTH_MASK) >> ATOM_PPLIB_PCIE_LINK_WIDTH_SHIFT) + 1;
 
        if (new_lane_width != current_lane_width) {
                radeon_set_pcie_lanes(rdev, new_lane_width);