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Message-ID: <YFZWW8IPhVff/VkS@pendragon.ideasonboard.com>
Date: Sat, 20 Mar 2021 22:08:59 +0200
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: quanyang.wang@...driver.com
Cc: Hyun Kwon <hyun.kwon@...inx.com>, David Airlie <airlied@...ux.ie>,
Daniel Vetter <daniel@...ll.ch>,
Michal Simek <michal.simek@...inx.com>,
dri-devel@...ts.freedesktop.org,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm: xlnx: zynqmp: release reset to DP controller before
accessing DP registers
Hi Quanyang,
Thank you for the patch.
On Sat, Mar 20, 2021 at 04:37:39PM +0800, quanyang.wang@...driver.com wrote:
> From: Quanyang Wang <quanyang.wang@...driver.com>
>
> When insmod zynqmp-dpsub.ko after rmmod it, system will hang with the
> error log as below:
>
> root@...inx-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@...inx-zynqmp:~# rmmod zynqmp_dpsub
> [ 94.023404] Console: switching to colour dummy device 80x25
> root@...inx-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@...driver.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.
For symmetry, should we also move the zynqmp_dp_reset() call from
zynqmp_dp_phy_exit() to zynqmp_dp_remove() ?
--
Regards,
Laurent Pinchart
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