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 <[email protected]>
Tested-by: Jérôme de Bretagne <[email protected]>
Bugzilla: https://gitlab.freedesktop.org/drm/intel/-/issues/3416
Fixes: 3d3721ccb18a ("drm/i915/dp: Extract drm_dp_read_downstream_info()")
Cc: <[email protected]> # 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
On Fri, Apr 30, 2021 at 06:34:27PM -0400, Lyude Paul wrote:
> 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 <[email protected]>
> Tested-by: J?r?me de Bretagne <[email protected]>
> Bugzilla: https://gitlab.freedesktop.org/drm/intel/-/issues/3416
> Fixes: 3d3721ccb18a ("drm/i915/dp: Extract drm_dp_read_downstream_info()")
> Cc: <[email protected]> # 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;
> +
Seems sane enough.
Reviewed-by: Ville Syrj?l? <[email protected]>
> if (dpcd[DP_DOWNSTREAMPORT_PRESENT] & DP_DETAILED_CAP_INFO_AVAILABLE)
> len *= 4;
>
> --
> 2.30.2
>
> _______________________________________________
> dri-devel mailing list
> [email protected]
> https://lists.freedesktop.org/mailman/listinfo/dri-devel
--
Ville Syrj?l?
Intel