Hi Laurent,

On 3/21/21 4:08 AM, Laurent Pinchart wrote:

Hi Quanyang,

Thank you for the patch.

On Sat, Mar 20, 2021 at 04:37:39PM +0800, quanyang.wang@windriver.com wrote:

...

From: Quanyang Wang quanyang.wang@windriver.com

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 quanyang.wang@windriver.com

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;
  

This change looks good to me.

...

ret = zynqmp_dp_phy_probe(dp); if (ret) return ret;

But shouldn't we call zynqmp_dp_reset(dp, true) here ? Or rather, call it in the error path at the end of the function, with a goto label.

Thank you for the suggestions.

zynqmp_dp_reset(dp, true) should be added in the error path, I will add this in the V2 patch.

For symmetry, should we also move the zynqmp_dp_reset() call from zynqmp_dp_phy_exit() to zynqmp_dp_remove() ?

Yes, I will move it out of zynqmp_dp_phy_exit and to zynqmp_dp_remove() in the V2 patch.

Thanks,

Quanyang