[PATCHv3] dmaengine: hsu: use kzalloc_flex()

[PATCHv3] 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. Assign counting variable
after allocation as required by __counted_by.

Apply the exact same treatment to struct hsu_dma and devm_kzalloc().

Signed-off-by: Rosen Penev <rosenp@gmail.com>
---
 v3: update description.
 v2: address review comments.
 drivers/dma/hsu/hsu.c | 45 ++++++++++++-------------------------------
 drivers/dma/hsu/hsu.h |  4 ++--
 2 files changed, 14 insertions(+), 35 deletions(-)

diff --git a/drivers/dma/hsu/hsu.c b/drivers/dma/hsu/hsu.c
index f62d60d7bc6b..78a2352ada8c 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->nr_channels = nr_channels;

-	hsu->chan = devm_kcalloc(chip->dev, hsu->nr_channels,
-				 sizeof(*hsu->chan), GFP_KERNEL);
-	if (!hsu->chan)
-		return -ENOMEM;
+	chip->hsu = hsu;

 	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

Re: [PATCHv3] dmaengine: hsu: use kzalloc_flex()

[Andy Shevchenko]

On Mon, Mar 30, 2026 at 11:44 PM Rosen Penev <rosenp@gmail.com> 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. Assign counting variable
> after allocation as required by __counted_by.
>
> Apply the exact same treatment to struct hsu_dma and devm_kzalloc().
>
> Signed-off-by: Rosen Penev <rosenp@gmail.com>
> ---
>  v3: update description.
>  v2: address review comments.

Wait a bit, I still get it unclear. Let's continue the discussion in v2.

-- 
With Best Regards,
Andy Shevchenko