linux-kernel - Re: [PATCH] drm/msm: Initialize mode

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Date:   Fri, 13 Jan 2023 06:23:22 +0200
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Bjorn Andersson <quic_bjorande@...cinc.com>,
        Rob Clark <robdclark@...il.com>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Johan Hovold <johan@...nel.org>
Cc:     Sean Paul <sean@...rly.run>, David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>, linux-arm-msm@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, freedreno@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/msm: Initialize mode_config earlier

On 13/01/2023 06:10, Bjorn Andersson wrote:
> Invoking drm_bridge_hpd_notify() on a drm_bridge with a HPD-enabled
> bridge_connector ends up in drm_bridge_connector_hpd_cb() calling
> drm_kms_helper_hotplug_event(), which assumes that the associated
> drm_device's mode_config.funcs is a valid pointer.
> 
> But in the MSM DisplayPort driver the HPD enablement happens at bind
> time and mode_config.funcs is initialized late in msm_drm_init(). This
> means that there's a window for hot plug events to dereference a NULL
> mode_config.funcs.
> 
> Move the assignment of mode_config.funcs before the bind, to avoid this
> scenario.

Cam we make DP driver not to report HPD events until the enable_hpd() 
was called? I think this is what was fixed by your internal_hpd patchset.

> 
> Reported-by: Johan Hovold <johan@...nel.org>
> Signed-off-by: Bjorn Andersson <quic_bjorande@...cinc.com>
> ---
>   drivers/gpu/drm/msm/msm_drv.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/msm_drv.c b/drivers/gpu/drm/msm/msm_drv.c
> index ee2f60b6f09b..7ac670f3e6ab 100644
> --- a/drivers/gpu/drm/msm/msm_drv.c
> +++ b/drivers/gpu/drm/msm/msm_drv.c
> @@ -438,6 +438,9 @@ static int msm_drm_init(struct device *dev, const struct drm_driver *drv)
>   
>   	drm_mode_config_init(ddev);
>   
> +	ddev->mode_config.funcs = &mode_config_funcs;
> +	ddev->mode_config.helper_private = &mode_config_helper_funcs;
> +
>   	ret = msm_init_vram(ddev);
>   	if (ret)
>   		return ret;
> @@ -479,9 +482,6 @@ static int msm_drm_init(struct device *dev, const struct drm_driver *drv)
>   
>   	drm_helper_move_panel_connectors_to_head(ddev);
>   
> -	ddev->mode_config.funcs = &mode_config_funcs;
> -	ddev->mode_config.helper_private = &mode_config_helper_funcs;
> -
>   	for (i = 0; i < priv->num_crtcs; i++) {
>   		/* initialize event thread */
>   		priv->event_thread[i].crtc_id = priv->crtcs[i]->base.id;

-- 
With best wishes
Dmitry