Subject: [PATCH] dmaengine: bcm2835-dma: Convert to use DMA pool

From: [email-masked] (Peter Ujfalusi)
Date: Tue, 17 Nov 2015 09:46:12 +0200

Hi,

On 11/16/2015 01:09 PM, Peter Ujfalusi wrote:
> f93178291712 dmaengine: bcm2835-dma: Fix memory leak when stopping a
> 	     running transfer
> 
> Fixed the memleak, but introduced another issue: the terminate_all callback
> might be called with interrupts disabled and the dma_free_coherent() is
> not allowed to be called when IRQs are disabled.
> Convert the driver to use dma_pool_* for managing the list of control
> blocks for the transfer.

FWIW: the patch has been tested and verified on Raspbery Pi:
https://github.com/raspberrypi/linux/pull/1178#issuecomment-157026794
https://github.com/raspberrypi/linux/pull/1178#issuecomment-157030190

It needed some modification since the Raspberry Pi kernel have non upstreamed
changes in bcm2835-dma driver (slave_sg support for example).

It would be great if this patch can make it to 4.4 as a fix.

Thanks,
P?ter

> 
> Fixes: f93178291712 ("dmaengine: bcm2835-dma: Fix memory leak when stopping a running transfer")
> Signed-off-by: Peter Ujfalusi <[email-masked]>
> ---
> Hi,
> 
> It was brought to my attention that the memleak fix broke the bcm2835 DMA. I did
> not noticed the use of dma_free_coherent() in the driver when I did the memleak
> fix.
> Since the driver does leaking memory every time the audio is stopped, the other
> option is to convert it to use DMA pool.
> I do not have access the Raspberry Pi, so I can not test this patch but it
> compiles ;)
> Can someone test this one out if it is working?
> 
> Regards,
> Peter
> 
>  drivers/dma/bcm2835-dma.c | 78 ++++++++++++++++++++++++++++++++---------------
>  1 file changed, 54 insertions(+), 24 deletions(-)
> 
> diff --git a/drivers/dma/bcm2835-dma.c b/drivers/dma/bcm2835-dma.c
> index c92d6a70ccf3..996c4b00d323 100644
> --- a/drivers/dma/bcm2835-dma.c
> +++ b/drivers/dma/bcm2835-dma.c
> @@ -31,6 +31,7 @@
>   */
>  #include <linux/dmaengine.h>
>  #include <linux/dma-mapping.h>
> +#include <linux/dmapool.h>
>  #include <linux/err.h>
>  #include <linux/init.h>
>  #include <linux/interrupt.h>
> @@ -62,6 +63,11 @@ struct bcm2835_dma_cb {
>  	uint32_t pad[2];
>  };
>  
> +struct bcm2835_cb_entry {
> +	struct bcm2835_dma_cb *cb;
> +	dma_addr_t paddr;
> +};
> +
>  struct bcm2835_chan {
>  	struct virt_dma_chan vc;
>  	struct list_head node;
> @@ -72,18 +78,18 @@ struct bcm2835_chan {
>  
>  	int ch;
>  	struct bcm2835_desc *desc;
> +	struct dma_pool *cb_pool;
>  
>  	void __iomem *chan_base;
>  	int irq_number;
>  };
>  
>  struct bcm2835_desc {
> +	struct bcm2835_chan *c;
>  	struct virt_dma_desc vd;
>  	enum dma_transfer_direction dir;
>  
> -	unsigned int control_block_size;
> -	struct bcm2835_dma_cb *control_block_base;
> -	dma_addr_t control_block_base_phys;
> +	struct bcm2835_cb_entry *cb_list;
>  
>  	unsigned int frames;
>  	size_t size;
> @@ -143,10 +149,13 @@ static inline struct bcm2835_desc *to_bcm2835_dma_desc(
>  static void bcm2835_dma_desc_free(struct virt_dma_desc *vd)
>  {
>  	struct bcm2835_desc *desc = container_of(vd, struct bcm2835_desc, vd);
> -	dma_free_coherent(desc->vd.tx.chan->device->dev,
> -			desc->control_block_size,
> -			desc->control_block_base,
> -			desc->control_block_base_phys);
> +	int i;
> +
> +	for (i = 0; i < desc->frames; i++)
> +		dma_pool_free(desc->c->cb_pool, desc->cb_list[i].cb,
> +			      desc->cb_list[i].paddr);
> +
> +	kfree(desc->cb_list);
>  	kfree(desc);
>  }
>  
> @@ -199,7 +208,7 @@ static void bcm2835_dma_start_desc(struct bcm2835_chan *c)
>  
>  	c->desc = d = to_bcm2835_dma_desc(&vd->tx);
>  
> -	writel(d->control_block_base_phys, c->chan_base + BCM2835_DMA_ADDR);
> +	writel(d->cb_list[0].paddr, c->chan_base + BCM2835_DMA_ADDR);
>  	writel(BCM2835_DMA_ACTIVE, c->chan_base + BCM2835_DMA_CS);
>  }
>  
> @@ -232,9 +241,16 @@ static irqreturn_t bcm2835_dma_callback(int irq, void *data)
>  static int bcm2835_dma_alloc_chan_resources(struct dma_chan *chan)
>  {
>  	struct bcm2835_chan *c = to_bcm2835_dma_chan(chan);
> +	struct device *dev = c->vc.chan.device->dev;
> +
> +	dev_dbg(dev, "Allocating DMA channel %d\n", c->ch);
>  
> -	dev_dbg(c->vc.chan.device->dev,
> -			"Allocating DMA channel %d\n", c->ch);
> +	c->cb_pool = dma_pool_create(dev_name(dev), dev,
> +				     sizeof(struct bcm2835_dma_cb), 0, 0);
> +	if (!c->cb_pool) {
> +		dev_err(dev, "unable to allocate descriptor pool\n");
> +		return -ENOMEM;
> +	}
>  
>  	return request_irq(c->irq_number,
>  			bcm2835_dma_callback, 0, "DMA IRQ", c);
> @@ -246,6 +262,7 @@ static void bcm2835_dma_free_chan_resources(struct dma_chan *chan)
>  
>  	vchan_free_chan_resources(&c->vc);
>  	free_irq(c->irq_number, c);
> +	dma_pool_destroy(c->cb_pool);
>  
>  	dev_dbg(c->vc.chan.device->dev, "Freeing DMA channel %u\n", c->ch);
>  }
> @@ -261,8 +278,7 @@ static size_t bcm2835_dma_desc_size_pos(struct bcm2835_desc *d, dma_addr_t addr)
>  	size_t size;
>  
>  	for (size = i = 0; i < d->frames; i++) {
> -		struct bcm2835_dma_cb *control_block =
> -			&d->control_block_base[i];
> +		struct bcm2835_dma_cb *control_block = d->cb_list[i].cb;
>  		size_t this_size = control_block->length;
>  		dma_addr_t dma;
>  
> @@ -343,6 +359,7 @@ static struct dma_async_tx_descriptor *bcm2835_dma_prep_dma_cyclic(
>  	dma_addr_t dev_addr;
>  	unsigned int es, sync_type;
>  	unsigned int frame;
> +	int i;
>  
>  	/* Grab configuration */
>  	if (!is_slave_direction(direction)) {
> @@ -374,27 +391,31 @@ static struct dma_async_tx_descriptor *bcm2835_dma_prep_dma_cyclic(
>  	if (!d)
>  		return NULL;
>  
> +	d->c = c;
>  	d->dir = direction;
>  	d->frames = buf_len / period_len;
>  
> -	/* Allocate memory for control blocks */
> -	d->control_block_size = d->frames * sizeof(struct bcm2835_dma_cb);
> -	d->control_block_base = dma_zalloc_coherent(chan->device->dev,
> -			d->control_block_size, &d->control_block_base_phys,
> -			GFP_NOWAIT);
> -
> -	if (!d->control_block_base) {
> +	d->cb_list = kcalloc(d->frames, sizeof(*d->cb_list), GFP_KERNEL);
> +	if (!d->cb_list) {
>  		kfree(d);
>  		return NULL;
>  	}
> +	/* Allocate memory for control blocks */
> +	for (i = 0; i < d->frames; i++) {
> +		struct bcm2835_cb_entry *cb_entry = &d->cb_list[i];
> +
> +		cb_entry->cb = dma_pool_zalloc(c->cb_pool, GFP_ATOMIC,
> +					       &cb_entry->paddr);
> +		if (!cb_entry->cb)
> +			goto error_cb;
> +	}
>  
>  	/*
>  	 * Iterate over all frames, create a control block
>  	 * for each frame and link them together.
>  	 */
>  	for (frame = 0; frame < d->frames; frame++) {
> -		struct bcm2835_dma_cb *control_block =
> -			&d->control_block_base[frame];
> +		struct bcm2835_dma_cb *control_block = d->cb_list[frame].cb;
>  
>  		/* Setup adresses */
>  		if (d->dir == DMA_DEV_TO_MEM) {
> @@ -428,12 +449,21 @@ static struct dma_async_tx_descriptor *bcm2835_dma_prep_dma_cyclic(
>  		 * This DMA engine driver currently only supports cyclic DMA.
>  		 * Therefore, wrap around at number of frames.
>  		 */
> -		control_block->next = d->control_block_base_phys +
> -			sizeof(struct bcm2835_dma_cb)
> -			* ((frame + 1) % d->frames);
> +		control_block->next = d->cb_list[((frame + 1) % d->frames)].paddr;
>  	}
>  
>  	return vchan_tx_prep(&c->vc, &d->vd, flags);
> +error_cb:
> +	i--;
> +	for (; i >= 0; i--) {
> +		struct bcm2835_cb_entry *cb_entry = &d->cb_list[i];
> +
> +		dma_pool_free(c->cb_pool, cb_entry->cb, cb_entry->paddr);
> +	}
> +
> +	kfree(d->cb_list);
> +	kfree(d);
> +	return NULL;
>  }
>  
>  static int bcm2835_dma_slave_config(struct dma_chan *chan,
>