linux-kernel - Re: [PATCH v1 3/3] staging: media: ipu3: Stop streaming in inverse order of starting

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Message-ID: <594c28e3-67f6-bb80-4751-ae6dc9f34c7c@linux.intel.com>
Date: Fri, 5 Jul 2024 12:03:49 +0800
From: Bingbu Cao <bingbu.cao@...ux.intel.com>
To: Max Staudt <mstaudt@...omium.org>,
 Sakari Ailus <sakari.ailus@...ux.intel.com>,
 Bingbu Cao <bingbu.cao@...el.com>, Tianshu Qiu <tian.shu.qiu@...el.com>,
 Mauro Carvalho Chehab <mchehab@...nel.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
 Ricardo Ribalda <ribalda@...omium.org>
Subject: Re: [PATCH v1 3/3] staging: media: ipu3: Stop streaming in inverse
 order of starting

Max,

On 7/5/24 9:54 AM, Max Staudt wrote:
> Hi Bingbu,
> 
> Thanks for your review! Replies inline...
> 
> 
> On 7/4/24 4:03 PM, Bingbu Cao wrote:
>>> diff --git a/drivers/staging/media/ipu3/ipu3-v4l2.c b/drivers/staging/media/ipu3/ipu3-v4l2.c
>>> index 3ff390b04e1a..e7aee7e3db5b 100644
>>> --- a/drivers/staging/media/ipu3/ipu3-v4l2.c
>>> +++ b/drivers/staging/media/ipu3/ipu3-v4l2.c
>>> @@ -535,29 +535,51 @@ static void imgu_vb2_stop_streaming(struct vb2_queue *vq)
>>>           container_of(vq, struct imgu_video_device, vbq);
>>>       int r;
>>>       unsigned int pipe;
>>> +    bool stop_streaming = false;
>>>   +    /* Verify that the node had been setup with imgu_v4l2_node_setup() */
>>>       WARN_ON(!node->enabled);
>>>         pipe = node->pipe;
>>>       dev_dbg(dev, "Try to stream off node [%u][%u]", pipe, node->id);
>>> -    imgu_pipe = &imgu->imgu_pipe[pipe];
>>> -    r = v4l2_subdev_call(&imgu_pipe->imgu_sd.subdev, video, s_stream, 0);
>>> -    if (r)
>>> -        dev_err(&imgu->pci_dev->dev,
>>> -            "failed to stop subdev streaming\n");
>>
>> I guess the subdev streams API can help us on this, but current fix
>> looks fine for me.
> 
> I don't understand what you're referring to, since your comment is in relation to a block of existing code that I have merely shuffled around. Could you please elaborate?

I guess the real problem is the subdev s_stream cannot be called multiple
times, please correct me if I am wrong as I have not touch IPU3 for long
time. :)

You can ignore my previous comment - 's_stream' is fine here.

> 
> 
>>>   +    /*
>>> +     * When the first node of a streaming setup is stopped, the entire
>>> +     * pipeline needs to stop before individual nodes are disabled.
>>> +     * Perform the inverse of the initial setup.
>>> +     *
>>> +     * Part 1 - s_stream on the entire pipeline
>>
>> stream on or off? it is a little confusing.
> 
> I meant that s_stream(off) is called "on the entire pipeline".
> 
> Thanks, I'll rephrase this in v2 :)

:)

> 
> 
>>> +     */
>>>       mutex_lock(&imgu->streaming_lock);
>>> -    /* Was this the first node with streaming disabled? */
>>>       if (imgu->streaming) {
>>>           /* Yes, really stop streaming now */
>>>           dev_dbg(dev, "IMGU streaming is ready to stop");
>>>           r = imgu_s_stream(imgu, false);
>>>           if (!r)
>>>               imgu->streaming = false;
>>> +        stop_streaming = true;
>>>       }
>>> -
>>>       mutex_unlock(&imgu->streaming_lock);
>>>   +    /* Part 2 - s_stream on subdevs
>>> +     *
>>> +     * If we call s_stream multiple times, Linux v6.7's call_s_stream()
>>> +     * WARNs and aborts. Thus, disable all pipes at once, and only once.
>>> +     */
>>> +    if (stop_streaming) {
>>
>>> +        for_each_set_bit(pipe, imgu->css.enabled_pipes,
>>> +                 IMGU_MAX_PIPE_NUM) {
>>> +            imgu_pipe = &imgu->imgu_pipe[pipe];
>>> +
>>> +            r = v4l2_subdev_call(&imgu_pipe->imgu_sd.subdev,
>>> +                         video, s_stream, 0);
>>> +            if (r)
>>> +                dev_err(&imgu->pci_dev->dev,
>>> +                    "failed to stop subdev streaming\n");
>>> +        }
>>
>> Is it possible to move this loop into 'if (imgu->streaming)' above?
> 
> The point of separating the loop from 'if (imgu->streaming)', and why the stop_streaming variable exists, is to keep the loop out of the mutex's hot path. This follows the code in imgu_vb2_start_streaming(), as mentioned in the commit message.
> 
> Is it safe to do this work with the mutex taken?
> 
> Is there any need to do this work with the mutex taken?
> 
> Should the streamoff path really be different from the streamon path?
> 
> Does this mean that the streamon path should also have this happen with the mutex taken?

Just a nit, stop_stream and s_stream only happen after imgu_s_stream(), so I
think they can be together and no need 'stop_streaming'. I think the mutex
is mainly for imgu_s_stream, subdev stream on/off should work without it.
It depends on you. :)

It'll be better that others who is still working on IPU3 devices can review.

Besides,
Reviewed-by: Bingbu Cao <bingbu.cao@...el.com>
> 
> 
> 
> Thanks,
> 
> Max
> 
> 

-- 
Best regards,
Bingbu Cao