linux-kernel - Re: [PATCH] drm/msm/dp: Drop aux devices together with DP controller

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Date:   Tue, 13 Jun 2023 13:51:06 -0700
From:   Abhinav Kumar <quic_abhinavk@...cinc.com>
To:     Doug Anderson <dianders@...omium.org>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
CC:     Bjorn Andersson <quic_bjorande@...cinc.com>,
        Rob Clark <robdclark@...il.com>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        "Kuogee Hsieh" <quic_khsieh@...cinc.com>,
        Johan Hovold <johan+linaro@...nel.org>,
        "Sean Paul" <sean@...rly.run>, David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Stephen Boyd <swboyd@...omium.org>,
        Vinod Polimera <quic_vpolimer@...cinc.com>,
        <linux-arm-msm@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
        <freedreno@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>,
        Sankeerth Billakanti <quic_sbillaka@...cinc.com>
Subject: Re: [PATCH] drm/msm/dp: Drop aux devices together with DP controller

Hi Doug

On 6/13/2023 12:33 PM, Doug Anderson wrote:
> Hi,
> 
> On Mon, Jun 12, 2023 at 3:40 PM Dmitry Baryshkov
> <dmitry.baryshkov@...aro.org> wrote:
>>
>> On 13/06/2023 01:01, Bjorn Andersson wrote:
>>> Using devres to depopulate the aux bus made sure that upon a probe
>>> deferral the EDP panel device would be destroyed and recreated upon next
>>> attempt.
>>>
>>> But the struct device which the devres is tied to is the DPUs
>>> (drm_dev->dev), which may be happen after the DP controller is torn
>>> down.
>>>
>>> Indications of this can be seen in the commonly seen EDID-hexdump full
>>> of zeros in the log, or the occasional/rare KASAN fault where the
>>> panel's attempt to read the EDID information causes a use after free on
>>> DP resources.
>>>
>>> It's tempting to move the devres to the DP controller's struct device,
>>> but the resources used by the device(s) on the aux bus are explicitly
>>> torn down in the error path.
>>
>> I hoped that proper usage of of_dp_aux_populate_bus(), with the callback
>> function being non-NULL would have solved at least this part. But it
>> seems I'll never see this patch.
> 
> Agreed. This has been pending for > 1 year now with no significant
> progress. Abhinav: Is there anything that can be done about this? Not
> following up on agreed-to cleanups in a timely manner doesn't set a
> good precedent. Next time the Qualcomm display wants to land something
> and promises to land a followup people will be less likely to believe
> them...
> 

Both QC and Google know there were other factors which delayed this last 
3-4 months.

But, I do not have any concrete justification to give you for the delays 
before that apart from perhaps other higher priority chrome and upstream 
bugs which kept cropping up.

Hence, all I can offer is my apologies for the delay.

After seeing this patch on the list, we have revived this effort now and 
re-assigned this within our team to take over from where that was left 
off. It will need some time to transition but this will see the end of 
the tunnel soon.

Thanks

Abhinav