While the DP specification isn't entirely clear on if this should be
allowed or not, some branch devices report having downstream ports present
while also reporting a downstream port count of 0. So to avoid breaking
those devices, we need to handle this in drm_dp_read_downstream_info().
So, to do this we assume there's no downstream port info when the
downstream port count is 0.
Signed-off-by: Lyude Paul <lyude(a)redhat.com>
Tested-by: Jérôme de Bretagne <jerome.debretagne(a)gmail.com>
Bugzilla: https://gitlab.freedesktop.org/drm/intel/-/issues/3416
Fixes: 3d3721ccb18a ("drm/i915/dp: Extract drm_dp_read_downstream_info()")
Cc: <stable(a)vger.kernel.org> # v5.10+
---
drivers/gpu/drm/drm_dp_helper.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
index cb56d74e9d38..27c8c5bdf7d9 100644
--- a/drivers/gpu/drm/drm_dp_helper.c
+++ b/drivers/gpu/drm/drm_dp_helper.c
@@ -682,7 +682,14 @@ int drm_dp_read_downstream_info(struct drm_dp_aux *aux,
!(dpcd[DP_DOWNSTREAMPORT_PRESENT] & DP_DWN_STRM_PORT_PRESENT))
return 0;
+ /* Some branches advertise having 0 downstream ports, despite also advertising they have a
+ * downstream port present. The DP spec isn't clear on if this is allowed or not, but since
+ * some branches do it we need to handle it regardless.
+ */
len = drm_dp_downstream_port_count(dpcd);
+ if (!len)
+ return 0;
+
if (dpcd[DP_DOWNSTREAMPORT_PRESENT] & DP_DETAILED_CAP_INFO_AVAILABLE)
len *= 4;
--
2.30.2
Hi Greg,
Attached is the backport of 1d7ba0165d82 ("mips: Do not include hi and lo
in clobber list for R6") for 4.14-stable.
It will also need two more commits (attached).
1690905240fd ("MIPS: Introduce isa-rev.h to define MIPS_ISA_REV")
18ba210a29d0 ("MIPS: cpu-features.h: Replace __mips_isa_rev with MIPS_ISA_REV")
--
Regards
Sudip