Hi Tomi,
Thank you for the patch.
On Tue, Mar 12, 2024 at 10:51:15AM +0200, Tomi Valkeinen wrote:
> The driver creates a bridge, but never calls drm_bridge_add() when
> non-live input is used. This leaves the bridge's hpd_mutex
> uninitialized, leading to:
>
> WARNING: CPU: 0 PID: 9 at kernel/locking/mutex.c:582 __mutex_lock+0x708/0x840
>
> Add the bridge add & remove calls so that the bridge gets managed
> correctly.
>
> Signed-off-by: Tomi Valkeinen <tomi.valkeinen@xxxxxxxxxxxxxxxx>
> Fixes: 561671612394 ("drm: xlnx: zynqmp_dpsub: Add support for live video input")
> ---
> drivers/gpu/drm/xlnx/zynqmp_dp.c | 4 ++++
> drivers/gpu/drm/xlnx/zynqmp_dpsub.c | 4 ----
> 2 files changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/xlnx/zynqmp_dp.c b/drivers/gpu/drm/xlnx/zynqmp_dp.c
> index a0606fab0e22..9f750740dfb8 100644
> --- a/drivers/gpu/drm/xlnx/zynqmp_dp.c
> +++ b/drivers/gpu/drm/xlnx/zynqmp_dp.c
> @@ -1761,6 +1761,8 @@ int zynqmp_dp_probe(struct zynqmp_dpsub *dpsub)
>
> dpsub->dp = dp;
>
> + drm_bridge_add(dpsub->bridge);
> +
This means that the bridge will be exposed to users before
zynqmp_disp_probe() is called, opening the door to a potential
use-before-init. The risk is mostly theoretical at this point I believe,
but it's still not a direction I'd like to that. Could you call
drm_bridge_add() in zynqmp_dpsub_probe(), between zynqmp_disp_probe()
and zynqmp_dpsub_drm_init() ?
> dev_dbg(dp->dev, "ZynqMP DisplayPort Tx probed with %u lanes\n",
> dp->num_lanes);
>
> @@ -1789,4 +1791,6 @@ void zynqmp_dp_remove(struct zynqmp_dpsub *dpsub)
>
> zynqmp_dp_phy_exit(dp);
> zynqmp_dp_reset(dp, true);
> +
> + drm_bridge_remove(dpsub->bridge);
> }
> diff --git a/drivers/gpu/drm/xlnx/zynqmp_dpsub.c b/drivers/gpu/drm/xlnx/zynqmp_dpsub.c
> index 88eb33acd5f0..3933c4f1a44f 100644
> --- a/drivers/gpu/drm/xlnx/zynqmp_dpsub.c
> +++ b/drivers/gpu/drm/xlnx/zynqmp_dpsub.c
> @@ -260,8 +260,6 @@ static int zynqmp_dpsub_probe(struct platform_device *pdev)
> ret = zynqmp_dpsub_drm_init(dpsub);
> if (ret)
> goto err_disp;
> - } else {
> - drm_bridge_add(dpsub->bridge);
> }
>
> dev_info(&pdev->dev, "ZynqMP DisplayPort Subsystem driver probed");
> @@ -288,8 +286,6 @@ static void zynqmp_dpsub_remove(struct platform_device *pdev)
>
> if (dpsub->drm)
> zynqmp_dpsub_drm_cleanup(dpsub);
> - else
> - drm_bridge_remove(dpsub->bridge);
>
> zynqmp_disp_remove(dpsub);
> zynqmp_dp_remove(dpsub);
>
> ---
> base-commit: e8f897f4afef0031fe618a8e94127a0934896aba
> change-id: 20240312-xilinx-dp-lock-fix-cf68f43a7bab
--
Regards,
Laurent Pinchart
