Re: [PATCH] drm: xlnx: zynqmp: release reset to DP controller before accessing DP registers

From: Quanyang Wang <redacted>

When insmod zynqmp-dpsub.ko after rmmod it, system will hang with the
error log as below:

root@xilinx-zynqmp:~# insmod zynqmp-dpsub.ko
[   88.391289] [drm] Initialized zynqmp-dpsub 1.0.0 20130509 for fd4a0000.display on minor 0
[   88.529906] Console: switching to colour frame buffer device 128x48
[   88.549402] zynqmp-dpsub fd4a0000.display: [drm] fb0: zynqmp-dpsubdrm frame buffer device
[   88.571624] zynqmp-dpsub fd4a0000.display: ZynqMP DisplayPort Subsystem driver probed
root@xilinx-zynqmp:~# rmmod zynqmp_dpsub
[   94.023404] Console: switching to colour dummy device 80x25
root@xilinx-zynqmp:~# insmod zynqmp-dpsub.ko
	<hang here>

This is because that in zynqmp_dp_probe it tries to access some DP
registers while the DP controller is still in the reset state. When
running "rmmod zynqmp_dpsub", zynqmp_dp_reset(dp, true) in
zynqmp_dp_phy_exit is called to force the DP controller into the reset
state. Then insmod will call zynqmp_dp_probe to write to the DP registers,
but at this moment the DP controller isn't brought out of the reset state
since the function zynqmp_dp_reset(dp, false) is called later and this
will result the system hang.

Releasing the reset to DP controller before any read/write operation to it
will fix this issue.

Signed-off-by: Quanyang Wang <redacted>
---
 drivers/gpu/drm/xlnx/zynqmp_dp.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/xlnx/zynqmp_dp.c b/drivers/gpu/drm/xlnx/zynqmp_dp.c
index 99158ee67d02..bb45b3663d6b 100644
--- a/drivers/gpu/drm/xlnx/zynqmp_dp.c
+++ b/drivers/gpu/drm/xlnx/zynqmp_dp.c

@@ -402,10 +402,6 @@ static int zynqmp_dp_phy_init(struct zynqmp_dp *dp)
 		}
 	}
 
-	ret = zynqmp_dp_reset(dp, false);
-	if (ret < 0)
-		return ret;
-
 	zynqmp_dp_clr(dp, ZYNQMP_DP_PHY_RESET, ZYNQMP_DP_PHY_RESET_ALL_RESET);
 
 	/*

@@ -1682,6 +1678,10 @@ int zynqmp_dp_probe(struct zynqmp_dpsub *dpsub, struct drm_device *drm)
 		return PTR_ERR(dp->reset);
 	}
 
+	ret = zynqmp_dp_reset(dp, false);
+	if (ret < 0)
+		return ret;
+