linux-kernel - Re: [Freedreno] [PATCH] drm/msm/disp/dpu1: avoid clearing hw interrupts if hw

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Date:   Mon, 2 May 2022 09:10:01 -0700
From:   Abhinav Kumar <quic_abhinavk@...cinc.com>
To:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
CC:     Stephen Boyd <swboyd@...omium.org>,
        Vinod Polimera <quic_vpolimer@...cinc.com>,
        <devicetree@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
        <freedreno@...ts.freedesktop.org>, <linux-arm-msm@...r.kernel.org>,
        <quic_kalyant@...cinc.com>, <robdclark@...il.com>,
        <linux-kernel@...r.kernel.org>, <dianders@...omium.org>
Subject: Re: [Freedreno] [PATCH] drm/msm/disp/dpu1: avoid clearing hw
 interrupts if hw_intr is null during drm uninit



On 5/2/2022 1:05 AM, Dmitry Baryshkov wrote:
> On Mon, 2 May 2022 at 04:38, Abhinav Kumar <quic_abhinavk@...cinc.com> wrote:
>>
>> Looks like our new CI has given all the answers we need :) which is a
>> great win for the CI in my opinion.
>>
>> Take a look at this report :
>> https://gitlab.freedesktop.org/drm/msm/-/jobs/22015361
>>
>> This issue seems to be because this change
>> https://github.com/torvalds/linux/commit/169466d4e59ca204683998b7f45673ebf0eb2de6
>> is missing in our tree.
>>
>> Without this change, what happens is that we are not hitting the return
>> 0 because we check for ENODEV.
>>
>>
>>     /*
>>        * External bridges are mandatory for eDP interfaces: one has to
>>        * provide at least an eDP panel (which gets wrapped into
>> panel-bridge).
>>        *
>>        * For DisplayPort interfaces external bridges are optional, so
>>        * silently ignore an error if one is not present (-ENODEV).
>>        */
>>       rc = dp_parser_find_next_bridge(dp_priv->parser);
>>       if (!dp->is_edp && rc == -ENODEV)
>>           return 0;
>>
>> So, I think we should do both:
>>
>> 1) Since we are running CI on the tree, backport this change so that
>> this error path doesnt hit?
>>
>> 2) Add this protection as well because this shows that we can indeed hit
>> this path in EDEFER cases causing this crash.
> 
> I have been waiting for v2 for the last week or so. It should include
> a fixed Fixes tag and an updated description (which should note that
> this happens in the error path, etc) as requested by Stephen.
> 

Prior to the above CI report, we did not know what is the error path in 
which this happens and why.

Till then we were just speculating.

Now that we do, we can certainly add it and post a v2.

>>
>> Thanks
>>
>> Abhinav
>>
>> On 4/27/2022 3:53 AM, Dmitry Baryshkov wrote:
>>> On 27/04/2022 00:50, Stephen Boyd wrote:
>>>> Quoting Vinod Polimera (2022-04-25 23:02:11)
>>>>> Avoid clearing irqs and derefernce hw_intr when hw_intr is null.
>>>>
>>>> Presumably this is only the case when the display driver doesn't fully
>>>> probe and something probe defers? Can you clarify how this situation
>>>> happens?
>>>>
>>>>>
>>>>> BUG: Unable to handle kernel NULL pointer dereference at virtual
>>>>> address 0000000000000000
>>>>>
>>>>> Call trace:
>>>>>    dpu_core_irq_uninstall+0x50/0xb0
>>>>>    dpu_irq_uninstall+0x18/0x24
>>>>>    msm_drm_uninit+0xd8/0x16c
>>>>>    msm_drm_bind+0x580/0x5fc
>>>>>    try_to_bring_up_master+0x168/0x1c0
>>>>>    __component_add+0xb4/0x178
>>>>>    component_add+0x1c/0x28
>>>>>    dp_display_probe+0x38c/0x400
>>>>>    platform_probe+0xb0/0xd0
>>>>>    really_probe+0xcc/0x2c8
>>>>>    __driver_probe_device+0xbc/0xe8
>>>>>    driver_probe_device+0x48/0xf0
>>>>>    __device_attach_driver+0xa0/0xc8
>>>>>    bus_for_each_drv+0x8c/0xd8
>>>>>    __device_attach+0xc4/0x150
>>>>>    device_initial_probe+0x1c/0x28
>>>>>
>>>>> Fixes: a73033619ea ("drm/msm/dpu: squash dpu_core_irq into
>>>>> dpu_hw_interrupts")
>>>>
>>>> The fixes tag looks odd. In dpu_core_irq_uninstall() at that commit it
>>>> is dealing with 'irq_obj' which isn't a pointer. After commit
>>>> f25f656608e3 ("drm/msm/dpu: merge struct dpu_irq into struct
>>>> dpu_hw_intr") dpu_core_irq_uninstall() starts using 'hw_intr' which is
>>>> allocated on the heap. If we backported this patch to a place that had
>>>> a73033619ea without f25f656608e3 it wouldn't make any sense.
>>>
>>> I'd agree here. The following tag would be correct:
>>>
>>> Fixes: f25f656608e3 ("drm/msm/dpu: merge struct dpu_irq into struct
>>> dpu_hw_intr")
>>>
>>>
>>>>
>>>>> Signed-off-by: Vinod Polimera <quic_vpolimer@...cinc.com>
>>>>> ---
>>>>>    drivers/gpu/drm/msm/disp/dpu1/dpu_hw_interrupts.c | 3 +++
>>>>>    1 file changed, 3 insertions(+)
>>>>>
>>>>> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_interrupts.c
>>>>> b/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_interrupts.c
>>>>> index c515b7c..ab28577 100644
>>>>> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_interrupts.c
>>>>> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_interrupts.c
>>>>> @@ -599,6 +599,9 @@ void dpu_core_irq_uninstall(struct dpu_kms *dpu_kms)
>>>>>    {
>>>>>           int i;
>>>>>
>>>>> +       if (!dpu_kms->hw_intr)
>>>>> +               return;
>>>>> +
>>>>>           pm_runtime_get_sync(&dpu_kms->pdev->dev);
>>>>>           for (i = 0; i < dpu_kms->hw_intr->total_irqs; i++)
>>>
>>>
> 
> 
>