linux-kernel - Re: [PATCH 1/3] dmaengine: virt-dma: don't always free descriptor upon completion

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Date:	Thu, 24 Sep 2015 22:56:21 +0530
From:	Vinod Koul <vinod.koul@...el.com>
To:	Robert Jarzmik <robert.jarzmik@...e.fr>
Cc:	Daniel Mack <daniel@...que.org>,
	Haojian Zhuang <haojian.zhuang@...il.com>,
	Jun Nie <jun.nie@...aro.org>,
	Lars-Peter Clausen <lars@...afoo.de>,
	dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/3] dmaengine: virt-dma: don't always free descriptor
 upon completion

On Sun, Sep 06, 2015 at 01:40:52PM +0200, Robert Jarzmik wrote:
> @@ -29,7 +29,7 @@ dma_cookie_t vchan_tx_submit(struct dma_async_tx_descriptor *tx)
>  	spin_lock_irqsave(&vc->lock, flags);
>  	cookie = dma_cookie_assign(tx);
>  
> -	list_add_tail(&vd->node, &vc->desc_submitted);
> +	list_move_tail(&vd->node, &vc->desc_submitted);

I am not sure I follow this, why move ?

> +int vchan_tx_desc_free(struct dma_async_tx_descriptor *tx)
> +{
> +	struct virt_dma_chan *vc = to_virt_chan(tx->chan);
> +	struct virt_dma_desc *vd = to_virt_desc(tx);
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&vc->lock, flags);
> +	list_del(&vd->node);
> +	spin_unlock_irqrestore(&vc->lock, flags);
> +
> +	dev_dbg(vc->chan.device->dev, "vchan %p: txd %p[%x]: freeing\n",
> +		vc, vd, vd->tx.cookie);
> +	vc->desc_free(vd);
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(vchan_tx_desc_free);
this one seems okay, can you add comments here and also update documentation
for this

> @@ -96,9 +115,13 @@ void vchan_dma_desc_free_list(struct virt_dma_chan *vc, struct list_head *head)
>  	while (!list_empty(head)) {
>  		struct virt_dma_desc *vd = list_first_entry(head,
>  			struct virt_dma_desc, node);
> -		list_del(&vd->node);
> -		dev_dbg(vc->chan.device->dev, "txd %p: freeing\n", vd);
> -		vc->desc_free(vd);
> +		if (dmaengine_desc_test_reuse(&vd->tx)) {
> +			list_move_tail(&vd->node, &vc->desc_allocated);

should we check this if the list is to be freed? Why would anyone call free
except when cleaning up ?

>  static inline void vchan_free_chan_resources(struct virt_dma_chan *vc)
>  {
> +	struct virt_dma_desc *vd;
>  	unsigned long flags;
>  	LIST_HEAD(head);
>  
>  	spin_lock_irqsave(&vc->lock, flags);
>  	vchan_get_all_descriptors(vc, &head);
> +	list_for_each_entry(vd, &head, node)
> +		dmaengine_desc_clear_reuse(&vd->tx);

why do we want to do this, if we are freeing them

-- 
~Vinod
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