Re: [PATCHv4] dmaengine: hsu: use kzalloc_flex()

[Frank Li]

Subject

dmaengine: hsu: use kzalloc_flex() to simplify code

On Tue, Apr 14, 2026 at 08:27:53PM -0700, Rosen Penev wrote:
> Simplifies allocations by using a flexible array member in this struct.
%s/this struct/struct hsu_dma_sg and struct hsu_dma.

Frank
>
> Remove hsu_dma_alloc_desc(). It now offers no readability advantages in
> this single usage.
>
> Add __counted_by to get extra runtime analysis.
>
> Apply the exact same treatment to struct hsu_dma and devm_kzalloc().
>
> Signed-off-by: Rosen Penev <rosenp@xxxxxxxxx>
> ---
>  v4: move back counting variable assignment, as requested.
>  v3: update description.
>  v2: address review comments.
>  drivers/dma/hsu/hsu.c | 43 +++++++++++--------------------------------
>  drivers/dma/hsu/hsu.h |  4 ++--
>  2 files changed, 13 insertions(+), 34 deletions(-)
>
> diff --git a/drivers/dma/hsu/hsu.c b/drivers/dma/hsu/hsu.c
> index f62d60d7bc6b..b1dd4fd1109b 100644
> --- a/drivers/dma/hsu/hsu.c
> +++ b/drivers/dma/hsu/hsu.c
> @@ -241,28 +241,10 @@ int hsu_dma_do_irq(struct hsu_dma_chip *chip, unsigned short nr, u32 status)
>  }
>  EXPORT_SYMBOL_GPL(hsu_dma_do_irq);
>
> -static struct hsu_dma_desc *hsu_dma_alloc_desc(unsigned int nents)
> -{
> -	struct hsu_dma_desc *desc;
> -
> -	desc = kzalloc_obj(*desc, GFP_NOWAIT);
> -	if (!desc)
> -		return NULL;
> -
> -	desc->sg = kzalloc_objs(*desc->sg, nents, GFP_NOWAIT);
> -	if (!desc->sg) {
> -		kfree(desc);
> -		return NULL;
> -	}
> -
> -	return desc;
> -}
> -
>  static void hsu_dma_desc_free(struct virt_dma_desc *vdesc)
>  {
>  	struct hsu_dma_desc *desc = to_hsu_dma_desc(vdesc);
>
> -	kfree(desc->sg);
>  	kfree(desc);
>  }
>
> @@ -276,10 +258,15 @@ static struct dma_async_tx_descriptor *hsu_dma_prep_slave_sg(
>  	struct scatterlist *sg;
>  	unsigned int i;
>
> -	desc = hsu_dma_alloc_desc(sg_len);
> +	desc = kzalloc_flex(*desc, sg, sg_len, GFP_NOWAIT);
>  	if (!desc)
>  		return NULL;
>
> +	desc->nents = sg_len;
> +	desc->direction = direction;
> +	/* desc->active = 0 by kzalloc */
> +	desc->status = DMA_IN_PROGRESS;
> +
>  	for_each_sg(sgl, sg, sg_len, i) {
>  		desc->sg[i].addr = sg_dma_address(sg);
>  		desc->sg[i].len = sg_dma_len(sg);
> @@ -287,11 +274,6 @@ static struct dma_async_tx_descriptor *hsu_dma_prep_slave_sg(
>  		desc->length += sg_dma_len(sg);
>  	}
>
> -	desc->nents = sg_len;
> -	desc->direction = direction;
> -	/* desc->active = 0 by kzalloc */
> -	desc->status = DMA_IN_PROGRESS;
> -
>  	return vchan_tx_prep(&hsuc->vchan, &desc->vdesc, flags);
>  }
>
> @@ -428,22 +410,19 @@ int hsu_dma_probe(struct hsu_dma_chip *chip)
>  {
>  	struct hsu_dma *hsu;
>  	void __iomem *addr = chip->regs + chip->offset;
> +	unsigned short nr_channels;
>  	unsigned short i;
>  	int ret;
>
> -	hsu = devm_kzalloc(chip->dev, sizeof(*hsu), GFP_KERNEL);
> +	/* Calculate nr_channels from the IO space length */
> +	nr_channels = (chip->length - chip->offset) / HSU_DMA_CHAN_LENGTH;
> +	hsu = devm_kzalloc(chip->dev, struct_size(hsu, chan, nr_channels), GFP_KERNEL);
>  	if (!hsu)
>  		return -ENOMEM;
>
>  	chip->hsu = hsu;
>
> -	/* Calculate nr_channels from the IO space length */
> -	hsu->nr_channels = (chip->length - chip->offset) / HSU_DMA_CHAN_LENGTH;
> -
> -	hsu->chan = devm_kcalloc(chip->dev, hsu->nr_channels,
> -				 sizeof(*hsu->chan), GFP_KERNEL);
> -	if (!hsu->chan)
> -		return -ENOMEM;
> +	hsu->nr_channels = nr_channels;
>
>  	INIT_LIST_HEAD(&hsu->dma.channels);
>  	for (i = 0; i < hsu->nr_channels; i++) {
> diff --git a/drivers/dma/hsu/hsu.h b/drivers/dma/hsu/hsu.h
> index 3bca577b98a1..f6ca1014bccf 100644
> --- a/drivers/dma/hsu/hsu.h
> +++ b/drivers/dma/hsu/hsu.h
> @@ -71,11 +71,11 @@ struct hsu_dma_sg {
>  struct hsu_dma_desc {
>  	struct virt_dma_desc vdesc;
>  	enum dma_transfer_direction direction;
> -	struct hsu_dma_sg *sg;
>  	unsigned int nents;
>  	size_t length;
>  	unsigned int active;
>  	enum dma_status status;
> +	struct hsu_dma_sg sg[] __counted_by(nents);
>  };
>
>  static inline struct hsu_dma_desc *to_hsu_dma_desc(struct virt_dma_desc *vdesc)
> @@ -115,8 +115,8 @@ struct hsu_dma {
>  	struct dma_device		dma;
>
>  	/* channels */
> -	struct hsu_dma_chan		*chan;
>  	unsigned short			nr_channels;
> +	struct hsu_dma_chan		chan[] __counted_by(nr_channels);
>  };
>
>  static inline struct hsu_dma *to_hsu_dma(struct dma_device *ddev)
> --
> 2.53.0
>