linux-kernel - Re: [PATCH] drm/msm/dpu: protect ctl ops calls with validity checks

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Date: Thu, 20 Jun 2024 09:54:12 -0700
From: Abhinav Kumar <quic_abhinavk@...cinc.com>
To: Rob Clark <robdclark@...il.com>,
        Dmitry Baryshkov
	<dmitry.baryshkov@...aro.org>
CC: <freedreno@...ts.freedesktop.org>, Sean Paul <sean@...rly.run>,
        "Marijn
 Suijten" <marijn.suijten@...ainline.org>,
        David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>,
        <dri-devel@...ts.freedesktop.org>, <quic_jesszhan@...cinc.com>,
        <dan.carpenter@...aro.org>, <linux-arm-msm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/msm/dpu: protect ctl ops calls with validity checks



On 6/20/2024 9:41 AM, Rob Clark wrote:
> On Thu, Jun 20, 2024 at 6:08 AM Dmitry Baryshkov
> <dmitry.baryshkov@...aro.org> wrote:
>>
>> On Thu, 20 Jun 2024 at 00:27, Abhinav Kumar <quic_abhinavk@...cinc.com> wrote:
>>>
>>> dpu_encoder_helper_phys_cleanup() calls the ctl ops without checking if
>>> the ops are assigned causing discrepancy between its callers where the
>>> checks are performed and the API itself which does not.
>>>
>>> Two approaches can be taken: either drop the checks even in the caller
>>> OR add the checks even in dpu_encoder_helper_phys_cleanup().
>>>
>>> Adopt the latter approach as ctl ops are assigned revision based so may not
>>> be always assigned.
>>
>> NAK, these calls are always assigned. Please make sure that they are
>> documented as required and drop offending checks.
> 
> agreed, I'd rather see the obvious crash if somehow a required
> callback didn't get set up, than a subtle/silent problem.  It is
> easier to debug that way.
> 
> BR,
> -R

Thank you both for the review.

Yes, as I wrote in the commit text, there were two ways to go about it.
And looks like the consensus is to go with the other way (drop the checks).

I will update the v2 that way and I also update the documentation of the 
ctl op of interest to this patch that it is always expected to be assigned.

> 
>>>
>>> Fixes: d7d0e73f7de3 ("drm/msm/dpu: introduce the dpu_encoder_phys_* for writeback")
>>> Reported-by: Dan Carpenter <dan.carpenter@...aro.org>
>>> Closes: https://lore.kernel.org/all/464fbd84-0d1c-43c3-a40b-31656ac06456@moroto.mountain/T/
>>> Signed-off-by: Abhinav Kumar <quic_abhinavk@...cinc.com>
>>> ---
>>>   drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c | 9 ++++++---
>>>   1 file changed, 6 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
>>> index 708657598cce..7f7e6d4e974b 100644
>>> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
>>> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
>>> @@ -2180,9 +2180,12 @@ void dpu_encoder_helper_phys_cleanup(struct dpu_encoder_phys *phys_enc)
>>>          if (ctl->ops.reset_intf_cfg)
>>>                  ctl->ops.reset_intf_cfg(ctl, &intf_cfg);
>>>
>>> -       ctl->ops.trigger_flush(ctl);
>>> -       ctl->ops.trigger_start(ctl);
>>> -       ctl->ops.clear_pending_flush(ctl);
>>> +       if (ctl->ops.trigger_flush)
>>> +               ctl->ops.trigger_flush(ctl);
>>> +       if (ctl->ops.trigger_start)
>>> +               ctl->ops.trigger_start(ctl);
>>> +       if (ctl->ops.clear_pending_flush)
>>> +               ctl->ops.clear_pending_flush(ctl);
>>>   }
>>>
>>>   void dpu_encoder_helper_phys_setup_cdm(struct dpu_encoder_phys *phys_enc,
>>> --
>>> 2.44.0
>>>
>>
>>
>> --
>> With best wishes
>> Dmitry