linux-kernel - [PATCH 5.12 076/677] drm/dp_mst: Revise broadcast msg lct & lcr

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Date:   Wed, 12 May 2021 16:42:02 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Wayne Lin <Wayne.Lin@....com>,
        Lyude Paul <lyude@...hat.com>
Subject: [PATCH 5.12 076/677] drm/dp_mst: Revise broadcast msg lct & lcr

From: Wayne Lin <Wayne.Lin@....com>

commit 419e91ea3143bf26991442465ac64d9461e98d96 upstream.

[Why & How]
According to DP spec, broadcast message LCT equals to 1 and LCR equals
to 6. Current implementation is incorrect. Fix it.
In addition, revise a bit the hdr->rad handling to include broadcast
case.

Signed-off-by: Wayne Lin <Wayne.Lin@....com>
Cc: stable@...r.kernel.org
Reviewed-by: Lyude Paul <lyude@...hat.com>
Signed-off-by: Lyude Paul <lyude@...hat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210224101521.6713-2-Wayne.Lin@amd.com
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/gpu/drm/drm_dp_mst_topology.c |   13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -2829,10 +2829,15 @@ static int set_hdr_from_dst_qlock(struct
 	else
 		hdr->broadcast = 0;
 	hdr->path_msg = txmsg->path_msg;
-	hdr->lct = mstb->lct;
-	hdr->lcr = mstb->lct - 1;
-	if (mstb->lct > 1)
-		memcpy(hdr->rad, mstb->rad, mstb->lct / 2);
+	if (hdr->broadcast) {
+		hdr->lct = 1;
+		hdr->lcr = 6;
+	} else {
+		hdr->lct = mstb->lct;
+		hdr->lcr = mstb->lct - 1;
+	}
+
+	memcpy(hdr->rad, mstb->rad, hdr->lct / 2);
 
 	return 0;
 }