linux-kernel - Re: [PATCH v8 07/11] drm/panel: panel-simple: Stash DP AUX bus; allow using it for DDC

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Date:   Fri, 04 Jun 2021 21:40:28 +0530
From:   rajeevny@...eaurora.org
To:     Douglas Anderson <dianders@...omium.org>
Cc:     Andrzej Hajda <a.hajda@...sung.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Sam Ravnborg <sam@...nborg.org>, linux-arm-msm@...r.kernel.org,
        Linus W <linus.walleij@...aro.org>,
        Lyude Paul <lyude@...hat.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Steev Klimaszewski <steev@...i.org>, robdclark@...omium.org,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Thierry Reding <treding@...dia.com>,
        dri-devel@...ts.freedesktop.org,
        Stanislav Lisovskiy <stanislav.lisovskiy@...el.com>,
        Stephen Boyd <swboyd@...omium.org>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Thierry Reding <thierry.reding@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 07/11] drm/panel: panel-simple: Stash DP AUX bus; allow
 using it for DDC

Hi Doug,

>  	panel->no_hpd = of_property_read_bool(dev->of_node, "no-hpd");
>  	if (!panel->no_hpd) {
> @@ -708,6 +712,8 @@ static int panel_simple_probe(struct device *dev,
> const struct panel_desc *desc)
> 
>  		if (!panel->ddc)
>  			return -EPROBE_DEFER;
> +	} else if (aux) {
> +		panel->ddc = &aux->ddc;
>  	}

In panel_simple_probe(), the put_device(&panel->ddc->dev) call is 
causing issue when the aux->ddc is used to assign panel->ddc
It works well when "ddc-i2c-bus" is used to assign panel->ddc

static int panel_simple_probe(...)
{
...

free_ddc:
         if (panel->ddc)
                 put_device(&panel->ddc->dev);

         return err;
}

== Log start ==

[    2.393970] ------------[ cut here ]------------
[    2.398747] kobject: '(null)' ((____ptrval____)): is not initialized, 
yet kobject_put() is being called.
[    2.408554] WARNING: CPU: 7 PID: 7 at lib/kobject.c:752 
kobject_put+0x38/0xe0
...
...
[    2.528574] Call trace:
[    2.531092]  kobject_put+0x38/0xe0
[    2.534594]  put_device+0x20/0x2c
[    2.538002]  panel_simple_probe+0x4bc/0x550
[    2.542300]  panel_simple_dp_aux_ep_probe+0x44/0x5c
[    2.547305]  dp_aux_ep_probe+0x58/0x80

== Log end ==


Sincerely,
Rajeev