[PATCHv2] dmaengine: st_fdma: simplify allocation

[PATCHv2] dmaengine: st_fdma: simplify allocation

[Rosen Penev]

Use a flexible array member to combine kzalloc and kcalloc to a single
allocation.

Add __counted_by for extra runtime analysis. Assign counting variable
after allocation before any array accesses.

Signed-off-by: Rosen Penev <rosenp@gmail.com>
---
 v2: update description.
 drivers/dma/st_fdma.c | 27 ++++++++-------------------
 drivers/dma/st_fdma.h |  4 ++--
 2 files changed, 10 insertions(+), 21 deletions(-)

diff --git a/drivers/dma/st_fdma.c b/drivers/dma/st_fdma.c
index d9547017f3bd..3ec0d6731b8d 100644
--- a/drivers/dma/st_fdma.c
+++ b/drivers/dma/st_fdma.c
@@ -710,16 +710,6 @@ static const struct of_device_id st_fdma_match[] = {
 };
 MODULE_DEVICE_TABLE(of, st_fdma_match);

-static int st_fdma_parse_dt(struct platform_device *pdev,
-			const struct st_fdma_driverdata *drvdata,
-			struct st_fdma_dev *fdev)
-{
-	snprintf(fdev->fw_name, FW_NAME_SIZE, "fdma_%s_%d.elf",
-		drvdata->name, drvdata->id);
-
-	return of_property_read_u32(pdev->dev.of_node, "dma-channels",
-				    &fdev->nr_channels);
-}
 #define FDMA_DMA_BUSWIDTHS	(BIT(DMA_SLAVE_BUSWIDTH_1_BYTE) | \
 				 BIT(DMA_SLAVE_BUSWIDTH_2_BYTES) | \
 				 BIT(DMA_SLAVE_BUSWIDTH_3_BYTES) | \
@@ -742,27 +732,26 @@ static int st_fdma_probe(struct platform_device *pdev)
 	struct st_fdma_dev *fdev;
 	struct device_node *np = pdev->dev.of_node;
 	const struct st_fdma_driverdata *drvdata;
+	u32 nr_channels;
 	int ret, i;

 	drvdata = device_get_match_data(&pdev->dev);

-	fdev = devm_kzalloc(&pdev->dev, sizeof(*fdev), GFP_KERNEL);
-	if (!fdev)
-		return -ENOMEM;
-
-	ret = st_fdma_parse_dt(pdev, drvdata, fdev);
+	ret = of_property_read_u32(pdev->dev.of_node, "dma-channels", &nr_channels);
 	if (ret) {
 		dev_err(&pdev->dev, "unable to find platform data\n");
-		goto err;
+		return ret;
 	}

-	fdev->chans = devm_kcalloc(&pdev->dev, fdev->nr_channels,
-				   sizeof(struct st_fdma_chan), GFP_KERNEL);
-	if (!fdev->chans)
+	fdev = devm_kzalloc(&pdev->dev, struct_size(fdev, chans, nr_channels), GFP_KERNEL);
+	if (!fdev)
 		return -ENOMEM;

+	fdev->nr_channels = nr_channels;
 	fdev->dev = &pdev->dev;
 	fdev->drvdata = drvdata;
+	snprintf(fdev->fw_name, FW_NAME_SIZE, "fdma_%s_%d.elf", drvdata->name, drvdata->id);
+
 	platform_set_drvdata(pdev, fdev);

 	fdev->irq = platform_get_irq(pdev, 0);
diff --git a/drivers/dma/st_fdma.h b/drivers/dma/st_fdma.h
index f1e746f7bc7d..27ded555879f 100644
--- a/drivers/dma/st_fdma.h
+++ b/drivers/dma/st_fdma.h
@@ -136,13 +136,13 @@ struct st_fdma_dev {

 	int irq;

-	struct st_fdma_chan *chans;
-
 	spinlock_t dreq_lock;
 	unsigned long dreq_mask;

 	u32 nr_channels;
 	char fw_name[FW_NAME_SIZE];
+
+	struct st_fdma_chan chans[] __counted_by(nr_channels);
 };

 /* Peripheral Registers*/
--
2.54.0

Re: [PATCHv2] dmaengine: st_fdma: simplify allocation

[Frank Li]

On Sun, Jun 07, 2026 at 10:18:29PM -0700, Rosen Penev wrote:

Nit: dmaengine: st_fdma: simplify allocation by using flexible array

Reviewed-by: Frank Li <Frank.Li@nxp.com>

> Use a flexible array member to combine kzalloc and kcalloc to a single
> allocation.
>
> Add __counted_by for extra runtime analysis. Assign counting variable
> after allocation before any array accesses.
>
> Signed-off-by: Rosen Penev <rosenp@gmail.com>
> ---
>

Re: [PATCHv2] dmaengine: st_fdma: simplify allocation

[Rosen Penev]

On Mon, Jun 8, 2026 at 9:25 AM Frank Li <Frank.li@oss.nxp.com> wrote:
>
> On Sun, Jun 07, 2026 at 10:18:29PM -0700, Rosen Penev wrote:
>
> Nit: dmaengine: st_fdma: simplify allocation by using flexible array
that's in the description. Did it that was to not have it as long,

flexible array member is the proper terminology.
>
> Reviewed-by: Frank Li <Frank.Li@nxp.com>
>
> > Use a flexible array member to combine kzalloc and kcalloc to a single
> > allocation.
> >
> > Add __counted_by for extra runtime analysis. Assign counting variable
> > after allocation before any array accesses.
> >
> > Signed-off-by: Rosen Penev <rosenp@gmail.com>
> > ---
> >

Re: [PATCHv2] dmaengine: st_fdma: simplify allocation

[Frank Li]

On Mon, Jun 08, 2026 at 01:52:09PM -0700, Rosen Penev wrote:
> On Mon, Jun 8, 2026 at 9:25 AM Frank Li <Frank.li@oss.nxp.com> wrote:
> >
> > On Sun, Jun 07, 2026 at 10:18:29PM -0700, Rosen Penev wrote:
> >
> > Nit: dmaengine: st_fdma: simplify allocation by using flexible array
> that's in the description. Did it that was to not have it as long,
>
> flexible array member is the proper terminology.

subject should provide most important information and summary what you did.
prefer pattern is

	do what for ...

	It is too general (simplify allocation\fix wraning\....)


Frank

> >
> > Reviewed-by: Frank Li <Frank.Li@nxp.com>
> >
> > > Use a flexible array member to combine kzalloc and kcalloc to a single
> > > allocation.
> > >
> > > Add __counted_by for extra runtime analysis. Assign counting variable
> > > after allocation before any array accesses.
> > >
> > > Signed-off-by: Rosen Penev <rosenp@gmail.com>
> > > ---
> > >