[PATCH] dmaengine: hsu: use kzalloc_flex

[PATCH] dmaengine: hsu: use kzalloc_flex

[Rosen Penev]

Simplifies allocations by using a flexible array member in this struct.

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@gmail.com>
---
 drivers/dma/hsu/hsu.c | 37 ++++++++-----------------------------
 drivers/dma/hsu/hsu.h |  4 ++--
 2 files changed, 10 insertions(+), 31 deletions(-)

diff --git a/drivers/dma/hsu/hsu.c b/drivers/dma/hsu/hsu.c
index f62d60d7bc6b..150c6567eede 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 +258,12 @@ 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;
+
 	for_each_sg(sgl, sg, sg_len, i) {
 		desc->sg[i].addr = sg_dma_address(sg);
 		desc->sg[i].len = sg_dma_len(sg);
@@ -287,7 +271,6 @@ 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;
@@ -430,21 +413,17 @@ int hsu_dma_probe(struct hsu_dma_chip *chip)
 	void __iomem *addr = chip->regs + chip->offset;
 	unsigned short i;
 	int ret;
+	unsigned short nr_channels;
 
-	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;
 
+	hsu->nr_channels = nr_channels;
 	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;
-
 	INIT_LIST_HEAD(&hsu->dma.channels);
 	for (i = 0; i < hsu->nr_channels; i++) {
 		struct hsu_dma_chan *hsuc = &hsu->chan[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

Re: [PATCH] dmaengine: hsu: use kzalloc_flex

[Andy Shevchenko]

On Thu, Mar 26, 2026 at 07:59:43PM -0700, Rosen Penev wrote:
> Simplifies allocations by using a flexible array member in this struct.
> 
> 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.

We refer to the functions in the comments and commit messages as func().
Please, update this patch accordingly.

...

>  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);

It can be collapsed to a single line, but for the sake of clarity the above is
okay.

>  }

...

> -	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->nents = sg_len;
>  	desc->direction = direction;
>  	/* desc->active = 0 by kzalloc */
>  	desc->status = DMA_IN_PROGRESS;

This nents move makes disruption is the field assignment block.
Please, move them all up.

...

>  	void __iomem *addr = chip->regs + chip->offset;
>  	unsigned short i;
>  	int ret;
> +	unsigned short nr_channels;

Preserve reversed xmas tree order.

...

> -	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;
>  
> +	hsu->nr_channels = nr_channels;

+ blank line.

>  	chip->hsu = hsu;

-- 
With Best Regards,
Andy Shevchenko