[AMD Official Use Only - Internal Distribution Only]
I took a closer look at this and there seems to be an issue in the function.
Crtc being null is a valid case here. The sequence that leads to this is,
unplug -> disable crtc/release vcpi slots then hotplug. The issue is that
pos->port is not guaranteed to be released in
drm_dp_atomic_release_vcpi_slots() so list_for_each_entry(pos,
&mst_state->vcpis, next) {} might still iterate thought it.
So, when a hotplug is done we still loop through the old port which has port! =
null, crtc = null, and vpci = 0. I didn't find anything that I can use to
remove the port from the list. So, a potential solution to this would be to add
a check for vpci = 0 and skip that port.
Thoughts/Suggestions?
Bhawan
________________________________
From: amd-gfx <[email protected]> on behalf of Lakha,
Bhawanpreet <[email protected]>
Sent: August 14, 2020 2:52 PM
To: Ruhl, Michael J <[email protected]>; Lipski, Mikita
<[email protected]>; Kazlauskas, Nicholas <[email protected]>;
Deucher, Alexander <[email protected]>
Cc: [email protected] <[email protected]>;
[email protected] <[email protected]>
Subject: Re: [PATCH] drm/dp_mst: Don't return error code when crtc is null
pos->port->connector?
This is checking the crtc not the connector. The crtc can be null if its
disabled.
Since it is happening after a unplug->hotplug, I guess we are missing something
in the disable sequence and the old connector is still in the list.
Bhawan
>>-----Original Message-----
>>From: dri-devel <[email protected]> On Behalf Of
>>Bhawanpreet Lakha
>>Sent: Friday, August 14, 2020 1:02 PM
>>To: [email protected]; [email protected];
>>[email protected]
>>Cc: Bhawanpreet Lakha <[email protected]>; dri-
>>[email protected]; [email protected]
>>Subject: [PATCH] drm/dp_mst: Don't return error code when crtc is null
>>
>>[Why]
>>In certain cases the crtc can be NULL and returning -EINVAL causes
>>atomic check to fail when it shouln't. This leads to valid
>>configurations failing because atomic check fails.
>
>So is this a bug fix or an exception case, or an expected possibility?
>
>From my reading of the function comments, it is not clear that
>pos->port->connector
>might be NULL for some reason.
>A better explanation of why this would occur would make this a much more
>useful commit message.
>
>My reading is that you ran into this issue an are masking it with this fix.
>
>Rather than this is a real possibility and this is the correct fix.
>
>Mike
>
>>[How]
>>Don't early return if crtc is null
>>
>>Signed-off-by: Bhawanpreet Lakha <[email protected]>
>>---
>> drivers/gpu/drm/drm_dp_mst_topology.c | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>
>>diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
>>b/drivers/gpu/drm/drm_dp_mst_topology.c
>>index 70c4b7afed12..bc90a1485699 100644
>>--- a/drivers/gpu/drm/drm_dp_mst_topology.c
>>+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
>>@@ -5037,8 +5037,8 @@ int drm_dp_mst_add_affected_dsc_crtcs(struct
>>drm_atomic_state *state, struct drm
>>
>> crtc = conn_state->crtc;
>>
>>- if (WARN_ON(!crtc))
>>- return -EINVAL;
>>+ if (!crtc)
>>+ continue;
>>
>> if (!drm_dp_mst_dsc_aux_for_port(pos->port))
>> continue;
>>--
>>2.17.1
>>
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