linux-kernel - [PATCH 2/3] drm: zynqmp_dp: Use smp

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Message-Id: <20251024191707.2310589-3-sean.anderson@linux.dev>
Date: Fri, 24 Oct 2025 15:17:06 -0400
From: Sean Anderson <sean.anderson@...ux.dev>
To: Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Tomi Valkeinen <tomi.valkeinen@...asonboard.com>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	dri-devel@...ts.freedesktop.org
Cc: linux-kernel@...r.kernel.org,
	David Airlie <airlied@...il.com>,
	Hyun Kwon <hyun.kwon@...inx.com>,
	Simona Vetter <simona@...ll.ch>,
	Michal Simek <michal.simek@....com>,
	linux-arm-kernel@...ts.infradead.org,
	Sean Anderson <sean.anderson@...ux.dev>
Subject: [PATCH 2/3] drm: zynqmp_dp: Use smp_load/store for status

dp->status is read asynchronously by the AUX bus. Therefore, all reads
outside of dp->lock must be atomic. Similarly, writes must be atomic as
well. Reads with dp->lock held do not need to be atomic.

Fixes: a7d5eeaa57d7 ("drm: zynqmp_dp: Add locking")
Signed-off-by: Sean Anderson <sean.anderson@...ux.dev>
---

 drivers/gpu/drm/xlnx/zynqmp_dp.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/xlnx/zynqmp_dp.c b/drivers/gpu/drm/xlnx/zynqmp_dp.c
index f39c78b08e6a..caf2e0ce3644 100644
--- a/drivers/gpu/drm/xlnx/zynqmp_dp.c
+++ b/drivers/gpu/drm/xlnx/zynqmp_dp.c
@@ -1111,7 +1111,7 @@ zynqmp_dp_aux_transfer(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg)
 			return msg->size;
 		}
 
-		if (dp->status == connector_status_disconnected) {
+		if (READ_ONCE(dp->status) == connector_status_disconnected) {
 			dev_dbg(dp->dev, "no connected aux device\n");
 			if (dp->ignore_aux_errors)
 				goto fake_response;
@@ -1697,7 +1697,7 @@ static enum drm_connector_status __zynqmp_dp_bridge_detect(struct zynqmp_dp *dp)
 	}
 
 	if (state & ZYNQMP_DP_INTERRUPT_SIGNAL_STATE_HPD) {
-		dp->status = connector_status_connected;
+		WRITE_ONCE(dp->status, connector_status_connected);
 		ret = drm_dp_dpcd_read(&dp->aux, 0x0, dp->dpcd,
 				       sizeof(dp->dpcd));
 		if (ret < 0) {
@@ -1716,7 +1716,7 @@ static enum drm_connector_status __zynqmp_dp_bridge_detect(struct zynqmp_dp *dp)
 	}
 
 disconnected:
-	dp->status = connector_status_disconnected;
+	WRITE_ONCE(dp->status, connector_status_disconnected);
 	return connector_status_disconnected;
 }
 
-- 
2.35.1.1320.gc452695387.dirty