Re: [PATCH v3 3/5] media: qcom: camss: vfe: Fix VFE reset while another line is streaming

[Bryan O'Donoghue <bod@kernel.org>]

On 28/09/2026 07:43, Hitesh Patel wrote:
> @@ -814,6 +814,7 @@ static int vfe_disable_output(struct vfe_line *line)
>   	struct vfe_output *output = &line->output;
>   	unsigned long flags;
>   	unsigned int i;
> +	bool last;
> 
>   	spin_lock_irqsave(&vfe->output_lock, flags);
>   	for (i = 0; i < output->wm_num; i++)
> @@ -821,6 +822,13 @@ static int vfe_disable_output(struct vfe_line *line)
>   	output->gen2.active_num = 0;
>   	spin_unlock_irqrestore(&vfe->output_lock, flags);
> 
> +	mutex_lock(&vfe->stream_lock);
> +	last = vfe->stream_count == 1;
> +	mutex_unlock(&vfe->stream_lock);
> +
> +	if (!last)
> +		return 0;
> +

NAK.

This can't be correct, in fact its very racy and will break. Here is the 
existing code.

static int vfe_disable_output(struct vfe_line *line)
{
         struct vfe_device *vfe = to_vfe(line);
         struct vfe_output *output = &line->output;
         unsigned long flags;
         unsigned int i;

         spin_lock_irqsave(&vfe->output_lock, flags);
         for (i = 0; i < output->wm_num; i++)
                 vfe->res->hw_ops->vfe_wm_stop(vfe, output->wm_idx[i]);
         output->gen2.active_num = 0;
         spin_unlock_irqrestore(&vfe->output_lock, flags);

         return vfe_reset(vfe);
}

/*
  * vfe_disable - Disable streaming on VFE line
  * @line: VFE line
  *
  * Return 0 on success or a negative error code otherwise
  */
int vfe_disable(struct vfe_line *line)
{
         struct vfe_device *vfe = to_vfe(line);
         int ret;

         ret = vfe_disable_output(line);
         if (ret)
                 goto error;

         vfe_put_output(line);

         mutex_lock(&vfe->stream_lock);

         vfe->stream_count--;

         mutex_unlock(&vfe->stream_lock);

error:
         return ret;
}

Here's how

stream_count = 2;

thread0:
   vfe_disable()
	vfe_disable_output()
	mutex_lock();
	last = stream_count == 1; //false
	mutex_unlock();
	return;

thread1:
   vfe_disable()
	vfe_disable_output()
	mutex_lock();
	last = stream_count == 1; //false
	mutex_unlock();
	return;

thread0:
   vfe_disable()
	mutex_lock();
	stream_count--; // => stream_count = 1;
	mutex_unlock();

thread1:
   vfe_disable()
	mutex_lock();
	stream_count--; // => stream_count = 0;
	mutex_unlock();

vfe_reset() is never called.

this->

diff --git a/drivers/media/platform/qcom/camss/camss-vfe.c 
b/drivers/media/platform/qcom/camss/camss-vfe.c
index 34e4319d8f80c..3dafd5d778630 100644
--- a/drivers/media/platform/qcom/camss/camss-vfe.c
+++ b/drivers/media/platform/qcom/camss/camss-vfe.c
@@ -828,7 +828,7 @@ static int vfe_disable_output(struct vfe_line *line)
         output->gen2.active_num = 0;
         spin_unlock_irqrestore(&vfe->output_lock, flags);

-       return vfe_reset(vfe);
+       return 0;
  }

  /*
@@ -850,7 +850,8 @@ int vfe_disable(struct vfe_line *line)

         mutex_lock(&vfe->stream_lock);

-       vfe->stream_count--;
+       if (--vfe->stream_count == 0)
+               ret = vfe_reset(vfe);

         mutex_unlock(&vfe->stream_lock);

---
bod