Re: [PATCH v3 04/12] media: staging: rkisp1: params: avoid using buffer if params is not streaming

[Tomasz Figa <tfiga@chromium.org>]

Hi Dafna,

On Tue, Sep 22, 2020 at 01:33:54PM +0200, Dafna Hirschfeld wrote:
> Currently, the first buffer queued in the params node is returned
> immediately to userspace and a copy of it is saved in the field
> 'cur_params'. The copy is later used for the first configuration
> when the stream is initiated by one of selfpath/mainpath capture nodes.

Thank you for the patch. Please see my comments inline.

> 
> There are 3 problems with this implementation:
> - The first params buffer is applied and returned to userspace even if
> userspace never calls to streamon on the params node.

How is this possible? VB2 doesn't call the .buf_queue callback until streaming is started.

> - If the first params buffer is queued after the stream started on the
> params node then it will return to userspace but will never be used.

Why?

> - The frame_sequence of the first buffer is set to -1 if the main/selfpath
> did not start streaming.

Indeed, this is invalid. The sequence number should correspond to the
sequence number of the frame that the parameters were applied to, i.e. the
parameter buffer A and the video buffer B dequeued from the CAPTURE node
which contains the first frame processed with the parameters from buffer A
should have the same sequence number.

> 
> A correct implementation is to apply the first params buffer when stream
> is started from mainpath/selfpath and only if params is also streaming.
> 
> The patch adds a new function 'rkisp1_params_apply_params_cfg' which takes
> a buffer from the buffers queue, apply it and returns it to userspace.
> The function is called from the irq handler and when main/selfpath stream
> starts - in the function 'rkisp1_params_config_parameter'
> 
> Also remove the fields 'cur_params', 'is_first_params' which are no
> more needed.
> 
> Signed-off-by: Dafna Hirschfeld <dafna.hirschfeld@collabora.com>
> Reported-by: kernel test robot <lkp@intel.com>
> Acked-by: Helen Koike <helen.koike@collabora.com>
> ---
> changes since v2:
> declare function 'rkisp1_params_apply_params_cfg' as static
> to fix a warning reported by 'kernel test robot <lkp@intel.com>'
> ---
>  drivers/staging/media/rkisp1/rkisp1-common.h |  4 --
>  drivers/staging/media/rkisp1/rkisp1-params.c | 50 ++++++++------------
>  2 files changed, 20 insertions(+), 34 deletions(-)
> 
> diff --git a/drivers/staging/media/rkisp1/rkisp1-common.h b/drivers/staging/media/rkisp1/rkisp1-common.h
> index 992d8ec4c448..232bee92d0eb 100644
> --- a/drivers/staging/media/rkisp1/rkisp1-common.h
> +++ b/drivers/staging/media/rkisp1/rkisp1-common.h
> @@ -262,10 +262,8 @@ struct rkisp1_stats {
>   * @rkisp1:		pointer to the rkisp1 device
>   * @config_lock:	locks the buffer list 'params' and 'is_streaming'
>   * @params:		queue of rkisp1_buffer
> - * @cur_params:		the first params values from userspace
>   * @vdev_fmt:		v4l2_format of the metadata format
>   * @is_streaming:	device is streaming
> - * @is_first_params:	the first params should take effect immediately
>   * @quantization:	the quantization configured on the isp's src pad
>   * @raw_type:		the bayer pattern on the isp video sink pad
>   */
> @@ -275,10 +273,8 @@ struct rkisp1_params {
>  
>  	spinlock_t config_lock; /* locks the buffers list 'params' and 'is_streaming' */
>  	struct list_head params;
> -	struct rkisp1_params_cfg cur_params;
>  	struct v4l2_format vdev_fmt;
>  	bool is_streaming;
> -	bool is_first_params;
>  
>  	enum v4l2_quantization quantization;
>  	enum rkisp1_fmt_raw_pat_type raw_type;
> diff --git a/drivers/staging/media/rkisp1/rkisp1-params.c b/drivers/staging/media/rkisp1/rkisp1-params.c
> index ab2deb57b1eb..e8049a50575f 100644
> --- a/drivers/staging/media/rkisp1/rkisp1-params.c
> +++ b/drivers/staging/media/rkisp1/rkisp1-params.c
> @@ -1185,23 +1185,14 @@ static void rkisp1_isp_isr_meas_config(struct rkisp1_params *params,
>  	}
>  }
>  
> -void rkisp1_params_isr(struct rkisp1_device *rkisp1)
> +static void rkisp1_params_apply_params_cfg(struct rkisp1_params *params,
> +					   unsigned int frame_sequence)

Should we call this _locked() since it is expected that the config_lock is
held when called?

To signify such condition, the __must_hold sparse annotation can be used.

>  {
> -	unsigned int frame_sequence = atomic_read(&rkisp1->isp.frame_sequence);
> -	struct rkisp1_params *params = &rkisp1->params;
>  	struct rkisp1_params_cfg *new_params;
>  	struct rkisp1_buffer *cur_buf = NULL;
>  
> -	spin_lock(&params->config_lock);
> -	if (!params->is_streaming) {
> -		spin_unlock(&params->config_lock);
> -		return;
> -	}
> -
> -	if (list_empty(&params->params)) {
> -		spin_unlock(&params->config_lock);
> +	if (list_empty(&params->params))
>  		return;
> -	}
>  
>  	cur_buf = list_first_entry(&params->params,
>  				   struct rkisp1_buffer, queue);
> @@ -1218,6 +1209,20 @@ void rkisp1_params_isr(struct rkisp1_device *rkisp1)
>  
>  	cur_buf->vb.sequence = frame_sequence;
>  	vb2_buffer_done(&cur_buf->vb.vb2_buf, VB2_BUF_STATE_DONE);
> +}
> +
> +void rkisp1_params_isr(struct rkisp1_device *rkisp1)
> +{
> +	unsigned int frame_sequence = atomic_read(&rkisp1->isp.frame_sequence);
> +	struct rkisp1_params *params = &rkisp1->params;
> +
> +	spin_lock(&params->config_lock);
> +	if (!params->is_streaming) {

Do we need this check? Wouldn't the queue be empty if params is not
streaming?

Also, if we decide that we need the check, we could replace the private
is_streaming flag with vb2_is_streaming().

Best regards,
Tomasz

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