[PATCH v2 00/13] dmaengine: introduce sg_nents_for_dma() and convert users

[PATCH v2 00/13] dmaengine: introduce sg_nents_for_dma() and convert users

[Andy Shevchenko]

A handful of the DMAengine drivers use same routine to calculate the number of
SG entries needed for the given DMA transfer. Provide a common helper for them
and convert.

I left the new helper on SG level of API because brief grepping shows potential
candidates outside of DMA engine, e.g.:

  drivers/crypto/chelsio/chcr_algo.c:154:  nents += DIV_ROUND_UP(less, entlen);
  drivers/spi/spi-stm32.c:1495:  /* Count the number of entries needed */

Changelog v2:
- dropped outdated patches (only 9 years passed :-)
- rebased on top of the current kernel
- left API SG wide It might

v1: https://patchwork.kernel.org/project/linux-dmaengine/patch/20161021173535.100245-1-andriy.shevchenko@linux.intel.com/

Andy Shevchenko (13):
  scatterlist: introduce sg_nents_for_dma() helper
  dmaengine: altera-msgdma: use sg_nents_for_dma() helper
  dmaengine: axi-dmac: use sg_nents_for_dma() helper
  dmaengine: bcm2835-dma: use sg_nents_for_dma() helper
  dmaengine: dw-axi-dmac: use sg_nents_for_dma() helper
  dmaengine: k3dma: use sg_nents_for_dma() helper
  dmaengine: lgm: use sg_nents_for_dma() helper
  dmaengine: pxa-dma: use sg_nents_for_dma() helper
  dmaengine: qcom: adm: use sg_nents_for_dma() helper
  dmaengine: qcom: bam_dma: use sg_nents_for_dma() helper
  dmaengine: sa11x0: use sg_nents_for_dma() helper
  dmaengine: sh: use sg_nents_for_dma() helper
  dmaengine: xilinx: xdma: use sg_nents_for_dma() helper

 drivers/dma/altera-msgdma.c                   |  5 ++--
 drivers/dma/bcm2835-dma.c                     | 19 +-------------
 drivers/dma/dma-axi-dmac.c                    |  5 +---
 .../dma/dw-axi-dmac/dw-axi-dmac-platform.c    |  6 ++---
 drivers/dma/k3dma.c                           |  9 ++-----
 drivers/dma/lgm/lgm-dma.c                     |  9 ++-----
 drivers/dma/pxa_dma.c                         |  5 ++--
 drivers/dma/qcom/bam_dma.c                    |  9 ++-----
 drivers/dma/qcom/qcom_adm.c                   |  9 +++----
 drivers/dma/sa11x0-dma.c                      |  6 ++---
 drivers/dma/sh/shdma-base.c                   |  5 ++--
 drivers/dma/xilinx/xdma.c                     |  6 ++---
 include/linux/scatterlist.h                   |  2 ++
 lib/scatterlist.c                             | 25 +++++++++++++++++++
 14 files changed, 51 insertions(+), 69 deletions(-)

-- 
2.50.1

[PATCH v2 01/13] scatterlist: introduce sg_nents_for_dma() helper

[Andy Shevchenko]

Sometimes the user needs to split each entry on the mapped scatter list
due to DMA length constrains. This helper returns a number of entities
assuming that each of them is not bigger than supplied maximum length.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
---
 include/linux/scatterlist.h |  2 ++
 lib/scatterlist.c           | 25 +++++++++++++++++++++++++
 2 files changed, 27 insertions(+)

diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
index 29f6ceb98d74..6de1a2434299 100644
--- a/include/linux/scatterlist.h
+++ b/include/linux/scatterlist.h
@@ -441,6 +441,8 @@ static inline void sg_init_marker(struct scatterlist *sgl,
 
 int sg_nents(struct scatterlist *sg);
 int sg_nents_for_len(struct scatterlist *sg, u64 len);
+int sg_nents_for_dma(struct scatterlist *sgl, unsigned int sglen, size_t len);
+
 struct scatterlist *sg_last(struct scatterlist *s, unsigned int);
 void sg_init_table(struct scatterlist *, unsigned int);
 void sg_init_one(struct scatterlist *, const void *, unsigned int);
diff --git a/lib/scatterlist.c b/lib/scatterlist.c
index 4af1c8b0775a..4d1a010f863c 100644
--- a/lib/scatterlist.c
+++ b/lib/scatterlist.c
@@ -64,6 +64,31 @@ int sg_nents_for_len(struct scatterlist *sg, u64 len)
 }
 EXPORT_SYMBOL(sg_nents_for_len);
 
+/**
+ * sg_nents_for_dma - return the count of DMA-capable entries in scatterlist
+ * @sgl:	The scatterlist
+ * @sglen:	The current number of entries
+ * @len:	The maximum length of DMA-capable block
+ *
+ * Description:
+ * Determines the number of entries in @sgl which would be permitted in
+ * DMA-capable transfer if list had been split accordingly, taking into
+ * account chaining as well.
+ *
+ * Returns:
+ *   the number of sgl entries needed
+ *
+ **/
+int sg_nents_for_dma(struct scatterlist *sgl, unsigned int sglen, size_t len)
+{
+	struct scatterlist *sg;
+	int i, nents = 0;
+
+	for_each_sg(sgl, sg, sglen, i)
+		nents += DIV_ROUND_UP(sg_dma_len(sg), len);
+	return nents;
+}
+
 /**
  * sg_last - return the last scatterlist entry in a list
  * @sgl:	First entry in the scatterlist
-- 
2.50.1

Re: [PATCH v2 01/13] scatterlist: introduce sg_nents_for_dma() helper

[Bjorn Andersson]

On Mon, Nov 10, 2025 at 11:23:28AM +0100, Andy Shevchenko wrote:
> Sometimes the user needs to split each entry on the mapped scatter list
> due to DMA length constrains. This helper returns a number of entities
> assuming that each of them is not bigger than supplied maximum length.
> 
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> ---
>  include/linux/scatterlist.h |  2 ++
>  lib/scatterlist.c           | 25 +++++++++++++++++++++++++
>  2 files changed, 27 insertions(+)
> 
> diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
> index 29f6ceb98d74..6de1a2434299 100644
> --- a/include/linux/scatterlist.h
> +++ b/include/linux/scatterlist.h
> @@ -441,6 +441,8 @@ static inline void sg_init_marker(struct scatterlist *sgl,
>  
>  int sg_nents(struct scatterlist *sg);
>  int sg_nents_for_len(struct scatterlist *sg, u64 len);
> +int sg_nents_for_dma(struct scatterlist *sgl, unsigned int sglen, size_t len);
> +
>  struct scatterlist *sg_last(struct scatterlist *s, unsigned int);
>  void sg_init_table(struct scatterlist *, unsigned int);
>  void sg_init_one(struct scatterlist *, const void *, unsigned int);
> diff --git a/lib/scatterlist.c b/lib/scatterlist.c
> index 4af1c8b0775a..4d1a010f863c 100644
> --- a/lib/scatterlist.c
> +++ b/lib/scatterlist.c
> @@ -64,6 +64,31 @@ int sg_nents_for_len(struct scatterlist *sg, u64 len)
>  }
>  EXPORT_SYMBOL(sg_nents_for_len);
>  
> +/**
> + * sg_nents_for_dma - return the count of DMA-capable entries in scatterlist
> + * @sgl:	The scatterlist
> + * @sglen:	The current number of entries
> + * @len:	The maximum length of DMA-capable block
> + *
> + * Description:
> + * Determines the number of entries in @sgl which would be permitted in
> + * DMA-capable transfer if list had been split accordingly, taking into
> + * account chaining as well.
> + *
> + * Returns:
> + *   the number of sgl entries needed
> + *
> + **/
> +int sg_nents_for_dma(struct scatterlist *sgl, unsigned int sglen, size_t len)
> +{
> +	struct scatterlist *sg;
> +	int i, nents = 0;
> +
> +	for_each_sg(sgl, sg, sglen, i)
> +		nents += DIV_ROUND_UP(sg_dma_len(sg), len);
> +	return nents;
> +}

We need an EXPORT_SYMBOL() here.

With that, this looks good to me.

Reviewed-by: Bjorn Andersson <andersson@kernel.org>

Regards,
Bjorn

> +
>  /**
>   * sg_last - return the last scatterlist entry in a list
>   * @sgl:	First entry in the scatterlist
> -- 
> 2.50.1
> 
> 

Re: [PATCH v2 01/13] scatterlist: introduce sg_nents_for_dma() helper

[Bjorn Andersson]

On Mon, Nov 10, 2025 at 09:05:26AM -0600, Bjorn Andersson wrote:
> On Mon, Nov 10, 2025 at 11:23:28AM +0100, Andy Shevchenko wrote:
> > Sometimes the user needs to split each entry on the mapped scatter list
> > due to DMA length constrains. This helper returns a number of entities
> > assuming that each of them is not bigger than supplied maximum length.
> > 
> > Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> > ---
> >  include/linux/scatterlist.h |  2 ++
> >  lib/scatterlist.c           | 25 +++++++++++++++++++++++++
> >  2 files changed, 27 insertions(+)
> > 
> > diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
> > index 29f6ceb98d74..6de1a2434299 100644
> > --- a/include/linux/scatterlist.h
> > +++ b/include/linux/scatterlist.h
> > @@ -441,6 +441,8 @@ static inline void sg_init_marker(struct scatterlist *sgl,
> >  
> >  int sg_nents(struct scatterlist *sg);
> >  int sg_nents_for_len(struct scatterlist *sg, u64 len);
> > +int sg_nents_for_dma(struct scatterlist *sgl, unsigned int sglen, size_t len);
> > +
> >  struct scatterlist *sg_last(struct scatterlist *s, unsigned int);
> >  void sg_init_table(struct scatterlist *, unsigned int);
> >  void sg_init_one(struct scatterlist *, const void *, unsigned int);
> > diff --git a/lib/scatterlist.c b/lib/scatterlist.c
> > index 4af1c8b0775a..4d1a010f863c 100644
> > --- a/lib/scatterlist.c
> > +++ b/lib/scatterlist.c
> > @@ -64,6 +64,31 @@ int sg_nents_for_len(struct scatterlist *sg, u64 len)
> >  }
> >  EXPORT_SYMBOL(sg_nents_for_len);
> >  
> > +/**
> > + * sg_nents_for_dma - return the count of DMA-capable entries in scatterlist
> > + * @sgl:	The scatterlist
> > + * @sglen:	The current number of entries
> > + * @len:	The maximum length of DMA-capable block
> > + *
> > + * Description:
> > + * Determines the number of entries in @sgl which would be permitted in
> > + * DMA-capable transfer if list had been split accordingly, taking into
> > + * account chaining as well.
> > + *
> > + * Returns:
> > + *   the number of sgl entries needed
> > + *
> > + **/
> > +int sg_nents_for_dma(struct scatterlist *sgl, unsigned int sglen, size_t len)

All but two clients store the value in an unsigned int. Changing the
return type to unsigned int also signals that the function is just
returning a count (no errors).

Regards,
Bjorn

> > +{
> > +	struct scatterlist *sg;
> > +	int i, nents = 0;
> > +
> > +	for_each_sg(sgl, sg, sglen, i)
> > +		nents += DIV_ROUND_UP(sg_dma_len(sg), len);
> > +	return nents;
> > +}
> 
> We need an EXPORT_SYMBOL() here.
> 
> With that, this looks good to me.
> 
> Reviewed-by: Bjorn Andersson <andersson@kernel.org>
> 
> Regards,
> Bjorn
> 
> > +
> >  /**
> >   * sg_last - return the last scatterlist entry in a list
> >   * @sgl:	First entry in the scatterlist
> > -- 
> > 2.50.1
> > 
> > 
> 

Re: [PATCH v2 01/13] scatterlist: introduce sg_nents_for_dma() helper

[Andy Shevchenko]

On Mon, Nov 10, 2025 at 09:21:18AM -0600, Bjorn Andersson wrote:
> On Mon, Nov 10, 2025 at 09:05:26AM -0600, Bjorn Andersson wrote:
> > On Mon, Nov 10, 2025 at 11:23:28AM +0100, Andy Shevchenko wrote:

...

> > >  int sg_nents(struct scatterlist *sg);
> > >  int sg_nents_for_len(struct scatterlist *sg, u64 len);
> > > +int sg_nents_for_dma(struct scatterlist *sgl, unsigned int sglen, size_t len);


^^^

> > > +int sg_nents_for_dma(struct scatterlist *sgl, unsigned int sglen, size_t len)
> 
> All but two clients store the value in an unsigned int. Changing the
> return type to unsigned int also signals that the function is just
> returning a count (no errors).

The type is chosen for the consistency with the existing APIs.
So, I prefer consistency in this case, if we need to change type, we need to do
that for all above APIs I believe. And this is out of the scope here.

Personally I was also puzzled of the choice as *nents members are all unsigned
int in the scatterlist.h.

...

> > We need an EXPORT_SYMBOL() here.

Good catch! I'll add it in next version.

> > With that, this looks good to me.
> > 
> > Reviewed-by: Bjorn Andersson <andersson@kernel.org>

Thanks!

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH v2 01/13] scatterlist: introduce sg_nents_for_dma() helper

[Bjorn Andersson]

On Mon, Nov 10, 2025 at 05:33:29PM +0200, Andy Shevchenko wrote:
> On Mon, Nov 10, 2025 at 09:21:18AM -0600, Bjorn Andersson wrote:
> > On Mon, Nov 10, 2025 at 09:05:26AM -0600, Bjorn Andersson wrote:
> > > On Mon, Nov 10, 2025 at 11:23:28AM +0100, Andy Shevchenko wrote:
> 
> ...
> 
> > > >  int sg_nents(struct scatterlist *sg);
> > > >  int sg_nents_for_len(struct scatterlist *sg, u64 len);
> > > > +int sg_nents_for_dma(struct scatterlist *sgl, unsigned int sglen, size_t len);
> 
> 
> ^^^
> 
> > > > +int sg_nents_for_dma(struct scatterlist *sgl, unsigned int sglen, size_t len)
> > 
> > All but two clients store the value in an unsigned int. Changing the
> > return type to unsigned int also signals that the function is just
> > returning a count (no errors).
> 
> The type is chosen for the consistency with the existing APIs.
> So, I prefer consistency in this case, if we need to change type, we need to do
> that for all above APIs I believe. And this is out of the scope here.
> 

That makes sense, after a second look I agree with your decision.

Regards,
Bjorn

> Personally I was also puzzled of the choice as *nents members are all unsigned
> int in the scatterlist.h.
> 
> ...
> 
> > > We need an EXPORT_SYMBOL() here.
> 
> Good catch! I'll add it in next version.
> 
> > > With that, this looks good to me.
> > > 
> > > Reviewed-by: Bjorn Andersson <andersson@kernel.org>
> 
> Thanks!
> 
> -- 
> With Best Regards,
> Andy Shevchenko
> 
> 

[PATCH v2 02/13] dmaengine: altera-msgdma: use sg_nents_for_dma() helper

[Andy Shevchenko]

Instead of open coded variant let's use recently introduced helper.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
---
 drivers/dma/altera-msgdma.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/dma/altera-msgdma.c b/drivers/dma/altera-msgdma.c
index a203fdd84950..48d2a0e638bb 100644
--- a/drivers/dma/altera-msgdma.c
+++ b/drivers/dma/altera-msgdma.c
@@ -396,13 +396,12 @@ msgdma_prep_slave_sg(struct dma_chan *dchan, struct scatterlist *sgl,
 	void *desc = NULL;
 	size_t len, avail;
 	dma_addr_t dma_dst, dma_src;
-	u32 desc_cnt = 0, i;
 	struct scatterlist *sg;
+	u32 desc_cnt;
 	u32 stride;
 	unsigned long irqflags;
 
-	for_each_sg(sgl, sg, sg_len, i)
-		desc_cnt += DIV_ROUND_UP(sg_dma_len(sg), MSGDMA_MAX_TRANS_LEN);
+	desc_cnt = sg_nents_for_dma(sgl, sg_len, MSGDMA_MAX_TRANS_LEN);
 
 	spin_lock_irqsave(&mdev->lock, irqflags);
 	if (desc_cnt > mdev->desc_free_cnt) {
-- 
2.50.1

[PATCH v2 03/13] dmaengine: axi-dmac: use sg_nents_for_dma() helper

[Andy Shevchenko]

Instead of open coded variant let's use recently introduced helper.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
---
 drivers/dma/dma-axi-dmac.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/drivers/dma/dma-axi-dmac.c b/drivers/dma/dma-axi-dmac.c
index 5b06b0dc67ee..5d4436e7d2ee 100644
--- a/drivers/dma/dma-axi-dmac.c
+++ b/drivers/dma/dma-axi-dmac.c
@@ -674,10 +674,7 @@ static struct dma_async_tx_descriptor *axi_dmac_prep_slave_sg(
 	if (direction != chan->direction)
 		return NULL;
 
-	num_sgs = 0;
-	for_each_sg(sgl, sg, sg_len, i)
-		num_sgs += DIV_ROUND_UP(sg_dma_len(sg), chan->max_length);
-
+	num_sgs = sg_nents_for_dma(sgl, sg_len, chan->max_length);
 	desc = axi_dmac_alloc_desc(chan, num_sgs);
 	if (!desc)
 		return NULL;
-- 
2.50.1

[PATCH v2 04/13] dmaengine: bcm2835-dma: use sg_nents_for_dma() helper

[Andy Shevchenko]

Instead of open coded variant let's use recently introduced helper.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
---
 drivers/dma/bcm2835-dma.c | 19 +------------------
 1 file changed, 1 insertion(+), 18 deletions(-)

diff --git a/drivers/dma/bcm2835-dma.c b/drivers/dma/bcm2835-dma.c
index 0117bb2e8591..802b23be2fd8 100644
--- a/drivers/dma/bcm2835-dma.c
+++ b/drivers/dma/bcm2835-dma.c
@@ -260,23 +260,6 @@ static void bcm2835_dma_create_cb_set_length(
 	control_block->info |= finalextrainfo;
 }
 
-static inline size_t bcm2835_dma_count_frames_for_sg(
-	struct bcm2835_chan *c,
-	struct scatterlist *sgl,
-	unsigned int sg_len)
-{
-	size_t frames = 0;
-	struct scatterlist *sgent;
-	unsigned int i;
-	size_t plength = bcm2835_dma_max_frame_length(c);
-
-	for_each_sg(sgl, sgent, sg_len, i)
-		frames += bcm2835_dma_frames_for_length(
-			sg_dma_len(sgent), plength);
-
-	return frames;
-}
-
 /**
  * bcm2835_dma_create_cb_chain - create a control block and fills data in
  *
@@ -672,7 +655,7 @@ static struct dma_async_tx_descriptor *bcm2835_dma_prep_slave_sg(
 	}
 
 	/* count frames in sg list */
-	frames = bcm2835_dma_count_frames_for_sg(c, sgl, sg_len);
+	frames = sg_nents_for_dma(sgl, sg_len, bcm2835_dma_max_frame_length(c));
 
 	/* allocate the CB chain */
 	d = bcm2835_dma_create_cb_chain(chan, direction, false,
-- 
2.50.1

[PATCH v2 05/13] dmaengine: dw-axi-dmac: use sg_nents_for_dma() helper

[Andy Shevchenko]

Instead of open coded variant let's use recently introduced helper.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
---
 drivers/dma/dw-axi-dmac/dw-axi-dmac-platform.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/dma/dw-axi-dmac/dw-axi-dmac-platform.c b/drivers/dma/dw-axi-dmac/dw-axi-dmac-platform.c
index b23536645ff7..493c2a32b0fe 100644
--- a/drivers/dma/dw-axi-dmac/dw-axi-dmac-platform.c
+++ b/drivers/dma/dw-axi-dmac/dw-axi-dmac-platform.c
@@ -850,7 +850,7 @@ dw_axi_dma_chan_prep_slave_sg(struct dma_chan *dchan, struct scatterlist *sgl,
 	unsigned int loop = 0;
 	struct scatterlist *sg;
 	size_t axi_block_len;
-	u32 len, num_sgs = 0;
+	u32 len, num_sgs;
 	unsigned int i;
 	dma_addr_t mem;
 	int status;
@@ -867,9 +867,7 @@ dw_axi_dma_chan_prep_slave_sg(struct dma_chan *dchan, struct scatterlist *sgl,
 	if (axi_block_len == 0)
 		return NULL;
 
-	for_each_sg(sgl, sg, sg_len, i)
-		num_sgs += DIV_ROUND_UP(sg_dma_len(sg), axi_block_len);
-
+	num_sgs = sg_nents_for_dma(sgl, sg_len, axi_block_len);
 	desc = axi_desc_alloc(num_sgs);
 	if (unlikely(!desc))
 		goto err_desc_get;
-- 
2.50.1

[PATCH v2 06/13] dmaengine: k3dma: use sg_nents_for_dma() helper

[Andy Shevchenko]

Instead of open coded variant let's use recently introduced helper.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
---
 drivers/dma/k3dma.c | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/drivers/dma/k3dma.c b/drivers/dma/k3dma.c
index acc2983e28e0..88f9a2952edc 100644
--- a/drivers/dma/k3dma.c
+++ b/drivers/dma/k3dma.c
@@ -536,19 +536,14 @@ static struct dma_async_tx_descriptor *k3_dma_prep_slave_sg(
 	size_t len, avail, total = 0;
 	struct scatterlist *sg;
 	dma_addr_t addr, src = 0, dst = 0;
-	int num = sglen, i;
+	int num, i;
 
 	if (sgl == NULL)
 		return NULL;
 
 	c->cyclic = 0;
 
-	for_each_sg(sgl, sg, sglen, i) {
-		avail = sg_dma_len(sg);
-		if (avail > DMA_MAX_SIZE)
-			num += DIV_ROUND_UP(avail, DMA_MAX_SIZE) - 1;
-	}
-
+	num = sg_nents_for_dma(sgl, sglen, DMA_MAX_SIZE);
 	ds = k3_dma_alloc_desc_resource(num, chan);
 	if (!ds)
 		return NULL;
-- 
2.50.1

[PATCH v2 07/13] dmaengine: lgm: use sg_nents_for_dma() helper

[Andy Shevchenko]

Instead of open coded variant let's use recently introduced helper.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
---
 drivers/dma/lgm/lgm-dma.c | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/drivers/dma/lgm/lgm-dma.c b/drivers/dma/lgm/lgm-dma.c
index 8173c3f1075a..7d4d3dde6d88 100644
--- a/drivers/dma/lgm/lgm-dma.c
+++ b/drivers/dma/lgm/lgm-dma.c
@@ -1164,8 +1164,8 @@ ldma_prep_slave_sg(struct dma_chan *chan, struct scatterlist *sgl,
 	struct dw2_desc *hw_ds;
 	struct dw2_desc_sw *ds;
 	struct scatterlist *sg;
-	int num = sglen, i;
 	dma_addr_t addr;
+	int num, i;
 
 	if (!sgl)
 		return NULL;
@@ -1173,12 +1173,7 @@ ldma_prep_slave_sg(struct dma_chan *chan, struct scatterlist *sgl,
 	if (d->ver > DMA_VER22)
 		return ldma_chan_desc_cfg(chan, sgl->dma_address, sglen);
 
-	for_each_sg(sgl, sg, sglen, i) {
-		avail = sg_dma_len(sg);
-		if (avail > DMA_MAX_SIZE)
-			num += DIV_ROUND_UP(avail, DMA_MAX_SIZE) - 1;
-	}
-
+	num = sg_nents_for_dma(sgl, sg_len, DMA_MAX_SIZE);
 	ds = dma_alloc_desc_resource(num, c);
 	if (!ds)
 		return NULL;
-- 
2.50.1

Re: [PATCH v2 07/13] dmaengine: lgm: use sg_nents_for_dma() helper

[Vinod Koul]

On 10-11-25, 11:23, Andy Shevchenko wrote:
> Instead of open coded variant let's use recently introduced helper.
> 
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> ---
>  drivers/dma/lgm/lgm-dma.c | 9 ++-------
>  1 file changed, 2 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/dma/lgm/lgm-dma.c b/drivers/dma/lgm/lgm-dma.c
> index 8173c3f1075a..7d4d3dde6d88 100644
> --- a/drivers/dma/lgm/lgm-dma.c
> +++ b/drivers/dma/lgm/lgm-dma.c
> @@ -1164,8 +1164,8 @@ ldma_prep_slave_sg(struct dma_chan *chan, struct scatterlist *sgl,
>  	struct dw2_desc *hw_ds;
>  	struct dw2_desc_sw *ds;
>  	struct scatterlist *sg;
> -	int num = sglen, i;
>  	dma_addr_t addr;
> +	int num, i;
>  
>  	if (!sgl)
>  		return NULL;
> @@ -1173,12 +1173,7 @@ ldma_prep_slave_sg(struct dma_chan *chan, struct scatterlist *sgl,
>  	if (d->ver > DMA_VER22)
>  		return ldma_chan_desc_cfg(chan, sgl->dma_address, sglen);
>  
> -	for_each_sg(sgl, sg, sglen, i) {
> -		avail = sg_dma_len(sg);
> -		if (avail > DMA_MAX_SIZE)
> -			num += DIV_ROUND_UP(avail, DMA_MAX_SIZE) - 1;
> -	}
> -
> +	num = sg_nents_for_dma(sgl, sg_len, DMA_MAX_SIZE);

drivers/dma/lgm/lgm-dma.c:1176:37: error: ‘sg_len’ undeclared (first use in this function); did you mean ‘sglen’?
         num = sg_nents_for_dma(sgl, sg_len, DMA_MAX_SIZE);

I am getting the build failure, as well as few unused warning with this,
pls fix

-- 
~Vinod

Re: [PATCH v2 07/13] dmaengine: lgm: use sg_nents_for_dma() helper

[Andy Shevchenko]

On Sat, Nov 22, 2025 at 02:58:05PM +0530, Vinod Koul wrote:
> On 10-11-25, 11:23, Andy Shevchenko wrote:
> > Instead of open coded variant let's use recently introduced helper.

...

> > +	num = sg_nents_for_dma(sgl, sg_len, DMA_MAX_SIZE);
> 
> drivers/dma/lgm/lgm-dma.c:1176:37: error: ‘sg_len’ undeclared (first use in this function); did you mean ‘sglen’?
>          num = sg_nents_for_dma(sgl, sg_len, DMA_MAX_SIZE);
> 
> I am getting the build failure, as well as few unused warning with this,
> pls fix

Indeed, sorry for that, in v4 should be fixed.
Thanks!

-- 
With Best Regards,
Andy Shevchenko

[PATCH v2 08/13] dmaengine: pxa-dma: use sg_nents_for_dma() helper

[Andy Shevchenko]

Instead of open coded variant let's use recently introduced helper.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
---
 drivers/dma/pxa_dma.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/dma/pxa_dma.c b/drivers/dma/pxa_dma.c
index 249296389771..b639c8b51e87 100644
--- a/drivers/dma/pxa_dma.c
+++ b/drivers/dma/pxa_dma.c
@@ -970,7 +970,7 @@ pxad_prep_slave_sg(struct dma_chan *dchan, struct scatterlist *sgl,
 	struct scatterlist *sg;
 	dma_addr_t dma;
 	u32 dcmd, dsadr = 0, dtadr = 0;
-	unsigned int nb_desc = 0, i, j = 0;
+	unsigned int nb_desc, i, j = 0;
 
 	if ((sgl == NULL) || (sg_len == 0))
 		return NULL;
@@ -979,8 +979,7 @@ pxad_prep_slave_sg(struct dma_chan *dchan, struct scatterlist *sgl,
 	dev_dbg(&chan->vc.chan.dev->device,
 		"%s(): dir=%d flags=%lx\n", __func__, dir, flags);
 
-	for_each_sg(sgl, sg, sg_len, i)
-		nb_desc += DIV_ROUND_UP(sg_dma_len(sg), PDMA_MAX_DESC_BYTES);
+	nb_desc = sg_nents_for_dma(sgl, sg_len, PDMA_MAX_DESC_BYTES);
 	sw_desc = pxad_alloc_desc(chan, nb_desc + 1);
 	if (!sw_desc)
 		return NULL;
-- 
2.50.1

[PATCH v2 09/13] dmaengine: qcom: adm: use sg_nents_for_dma() helper

[Andy Shevchenko]

Instead of open coded variant let's use recently introduced helper.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
---
 drivers/dma/qcom/qcom_adm.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/drivers/dma/qcom/qcom_adm.c b/drivers/dma/qcom/qcom_adm.c
index 6be54fddcee1..490edad20ae6 100644
--- a/drivers/dma/qcom/qcom_adm.c
+++ b/drivers/dma/qcom/qcom_adm.c
@@ -390,16 +390,15 @@ static struct dma_async_tx_descriptor *adm_prep_slave_sg(struct dma_chan *chan,
 	}
 
 	/* iterate through sgs and compute allocation size of structures */
-	for_each_sg(sgl, sg, sg_len, i) {
-		if (achan->slave.device_fc) {
+	if (achan->slave.device_fc) {
+		for_each_sg(sgl, sg, sg_len, i) {
 			box_count += DIV_ROUND_UP(sg_dma_len(sg) / burst,
 						  ADM_MAX_ROWS);
 			if (sg_dma_len(sg) % burst)
 				single_count++;
-		} else {
-			single_count += DIV_ROUND_UP(sg_dma_len(sg),
-						     ADM_MAX_XFER);
 		}
+	} else {
+		single_count = sg_nents_for_dma(sgl, sg_len, ADM_MAX_XFER);
 	}
 
 	async_desc = kzalloc(sizeof(*async_desc), GFP_NOWAIT);
-- 
2.50.1

Re: [PATCH v2 09/13] dmaengine: qcom: adm: use sg_nents_for_dma() helper

[Bjorn Andersson]

On Mon, Nov 10, 2025 at 11:23:36AM +0100, Andy Shevchenko wrote:
> Instead of open coded variant let's use recently introduced helper.
> 

Reviewed-by: Bjorn Andersson <andersson@kernel.org>

> Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> ---
>  drivers/dma/qcom/qcom_adm.c | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/dma/qcom/qcom_adm.c b/drivers/dma/qcom/qcom_adm.c
> index 6be54fddcee1..490edad20ae6 100644
> --- a/drivers/dma/qcom/qcom_adm.c
> +++ b/drivers/dma/qcom/qcom_adm.c
> @@ -390,16 +390,15 @@ static struct dma_async_tx_descriptor *adm_prep_slave_sg(struct dma_chan *chan,
>  	}
>  
>  	/* iterate through sgs and compute allocation size of structures */
> -	for_each_sg(sgl, sg, sg_len, i) {
> -		if (achan->slave.device_fc) {
> +	if (achan->slave.device_fc) {
> +		for_each_sg(sgl, sg, sg_len, i) {
>  			box_count += DIV_ROUND_UP(sg_dma_len(sg) / burst,
>  						  ADM_MAX_ROWS);
>  			if (sg_dma_len(sg) % burst)
>  				single_count++;
> -		} else {
> -			single_count += DIV_ROUND_UP(sg_dma_len(sg),
> -						     ADM_MAX_XFER);
>  		}
> +	} else {
> +		single_count = sg_nents_for_dma(sgl, sg_len, ADM_MAX_XFER);
>  	}
>  
>  	async_desc = kzalloc(sizeof(*async_desc), GFP_NOWAIT);
> -- 
> 2.50.1
> 
> 

[PATCH v2 10/13] dmaengine: qcom: bam_dma: use sg_nents_for_dma() helper

[Andy Shevchenko]

Instead of open coded variant let's use recently introduced helper.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
---
 drivers/dma/qcom/bam_dma.c | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/drivers/dma/qcom/bam_dma.c b/drivers/dma/qcom/bam_dma.c
index 2cf060174795..62b3921f0d11 100644
--- a/drivers/dma/qcom/bam_dma.c
+++ b/drivers/dma/qcom/bam_dma.c
@@ -655,22 +655,17 @@ static struct dma_async_tx_descriptor *bam_prep_slave_sg(struct dma_chan *chan,
 	struct scatterlist *sg;
 	u32 i;
 	struct bam_desc_hw *desc;
-	unsigned int num_alloc = 0;
-
+	unsigned int num_alloc;
 
 	if (!is_slave_direction(direction)) {
 		dev_err(bdev->dev, "invalid dma direction\n");
 		return NULL;
 	}
 
-	/* calculate number of required entries */
-	for_each_sg(sgl, sg, sg_len, i)
-		num_alloc += DIV_ROUND_UP(sg_dma_len(sg), BAM_FIFO_SIZE);
-
 	/* allocate enough room to accommodate the number of entries */
+	num_alloc = sg_nents_for_dma(sgl, sg_len, BAM_FIFO_SIZE);
 	async_desc = kzalloc(struct_size(async_desc, desc, num_alloc),
 			     GFP_NOWAIT);
-
 	if (!async_desc)
 		return NULL;
 
-- 
2.50.1

Re: [PATCH v2 10/13] dmaengine: qcom: bam_dma: use sg_nents_for_dma() helper

[Bjorn Andersson]

On Mon, Nov 10, 2025 at 11:23:37AM +0100, Andy Shevchenko wrote:
> Instead of open coded variant let's use recently introduced helper.
> 

Reviewed-by: Bjorn Andersson <andersson@kernel.org>

Regards,
Bjorn

> Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> ---
>  drivers/dma/qcom/bam_dma.c | 9 ++-------
>  1 file changed, 2 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/dma/qcom/bam_dma.c b/drivers/dma/qcom/bam_dma.c
> index 2cf060174795..62b3921f0d11 100644
> --- a/drivers/dma/qcom/bam_dma.c
> +++ b/drivers/dma/qcom/bam_dma.c
> @@ -655,22 +655,17 @@ static struct dma_async_tx_descriptor *bam_prep_slave_sg(struct dma_chan *chan,
>  	struct scatterlist *sg;
>  	u32 i;
>  	struct bam_desc_hw *desc;
> -	unsigned int num_alloc = 0;
> -
> +	unsigned int num_alloc;
>  
>  	if (!is_slave_direction(direction)) {
>  		dev_err(bdev->dev, "invalid dma direction\n");
>  		return NULL;
>  	}
>  
> -	/* calculate number of required entries */
> -	for_each_sg(sgl, sg, sg_len, i)
> -		num_alloc += DIV_ROUND_UP(sg_dma_len(sg), BAM_FIFO_SIZE);
> -
>  	/* allocate enough room to accommodate the number of entries */
> +	num_alloc = sg_nents_for_dma(sgl, sg_len, BAM_FIFO_SIZE);
>  	async_desc = kzalloc(struct_size(async_desc, desc, num_alloc),
>  			     GFP_NOWAIT);
> -
>  	if (!async_desc)
>  		return NULL;
>  
> -- 
> 2.50.1
> 
> 

[PATCH v2 11/13] dmaengine: sa11x0: use sg_nents_for_dma() helper

[Andy Shevchenko]

Instead of open coded variant let's use recently introduced helper.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
---
 drivers/dma/sa11x0-dma.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/dma/sa11x0-dma.c b/drivers/dma/sa11x0-dma.c
index dc1a9a05252e..3dd33d3f7987 100644
--- a/drivers/dma/sa11x0-dma.c
+++ b/drivers/dma/sa11x0-dma.c
@@ -526,7 +526,7 @@ static struct dma_async_tx_descriptor *sa11x0_dma_prep_slave_sg(
 	struct sa11x0_dma_chan *c = to_sa11x0_dma_chan(chan);
 	struct sa11x0_dma_desc *txd;
 	struct scatterlist *sgent;
-	unsigned i, j = sglen;
+	unsigned int i, j;
 	size_t size = 0;
 
 	/* SA11x0 channels can only operate in their native direction */
@@ -542,10 +542,7 @@ static struct dma_async_tx_descriptor *sa11x0_dma_prep_slave_sg(
 
 	for_each_sg(sg, sgent, sglen, i) {
 		dma_addr_t addr = sg_dma_address(sgent);
-		unsigned int len = sg_dma_len(sgent);
 
-		if (len > DMA_MAX_SIZE)
-			j += DIV_ROUND_UP(len, DMA_MAX_SIZE & ~DMA_ALIGN) - 1;
 		if (addr & DMA_ALIGN) {
 			dev_dbg(chan->device->dev, "vchan %p: bad buffer alignment: %pad\n",
 				&c->vc, &addr);
@@ -553,6 +550,7 @@ static struct dma_async_tx_descriptor *sa11x0_dma_prep_slave_sg(
 		}
 	}
 
+	j = sg_nents_for_dma(sgl, sg_len, DMA_MAX_SIZE & ~DMA_ALIGN);
 	txd = kzalloc(struct_size(txd, sg, j), GFP_ATOMIC);
 	if (!txd) {
 		dev_dbg(chan->device->dev, "vchan %p: kzalloc failed\n", &c->vc);
-- 
2.50.1

[PATCH v2 12/13] dmaengine: sh: use sg_nents_for_dma() helper

[Andy Shevchenko]

Instead of open coded variant let's use recently introduced helper.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
---
 drivers/dma/sh/shdma-base.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/dma/sh/shdma-base.c b/drivers/dma/sh/shdma-base.c
index 834741adadaa..1e1b65e46668 100644
--- a/drivers/dma/sh/shdma-base.c
+++ b/drivers/dma/sh/shdma-base.c
@@ -577,12 +577,11 @@ static struct dma_async_tx_descriptor *shdma_prep_sg(struct shdma_chan *schan,
 	struct scatterlist *sg;
 	struct shdma_desc *first = NULL, *new = NULL /* compiler... */;
 	LIST_HEAD(tx_list);
-	int chunks = 0;
+	int chunks;
 	unsigned long irq_flags;
 	int i;
 
-	for_each_sg(sgl, sg, sg_len, i)
-		chunks += DIV_ROUND_UP(sg_dma_len(sg), schan->max_xfer_len);
+	chunks = sg_nents_for_dma(sgl, sg_len, schan->max_xfer_len);
 
 	/* Have to lock the whole loop to protect against concurrent release */
 	spin_lock_irqsave(&schan->chan_lock, irq_flags);
-- 
2.50.1

[PATCH v2 13/13] dmaengine: xilinx: xdma: use sg_nents_for_dma() helper

[Andy Shevchenko]

Instead of open coded variant let's use recently introduced helper.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
---
 drivers/dma/xilinx/xdma.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/dma/xilinx/xdma.c b/drivers/dma/xilinx/xdma.c
index 5ecf8223c112..118199a04902 100644
--- a/drivers/dma/xilinx/xdma.c
+++ b/drivers/dma/xilinx/xdma.c
@@ -605,13 +605,11 @@ xdma_prep_device_sg(struct dma_chan *chan, struct scatterlist *sgl,
 	struct xdma_chan *xdma_chan = to_xdma_chan(chan);
 	struct dma_async_tx_descriptor *tx_desc;
 	struct xdma_desc *sw_desc;
-	u32 desc_num = 0, i;
 	u64 addr, dev_addr, *src, *dst;
+	u32 desc_num, i;
 	struct scatterlist *sg;
 
-	for_each_sg(sgl, sg, sg_len, i)
-		desc_num += DIV_ROUND_UP(sg_dma_len(sg), XDMA_DESC_BLEN_MAX);
-
+	desc_num = sg_nents_for_dma(sgl, sg_len, XDMA_DESC_BLEN_MAX);
 	sw_desc = xdma_alloc_desc(xdma_chan, desc_num, false);
 	if (!sw_desc)
 		return NULL;
-- 
2.50.1

Re: [PATCH v2 00/13] dmaengine: introduce sg_nents_for_dma() and convert users

[Bjorn Andersson]

On Mon, Nov 10, 2025 at 11:23:27AM +0100, Andy Shevchenko wrote:
> A handful of the DMAengine drivers use same routine to calculate the number of
> SG entries needed for the given DMA transfer. Provide a common helper for them
> and convert.
> 
> I left the new helper on SG level of API because brief grepping shows potential
> candidates outside of DMA engine, e.g.:
> 
>   drivers/crypto/chelsio/chcr_algo.c:154:  nents += DIV_ROUND_UP(less, entlen);
>   drivers/spi/spi-stm32.c:1495:  /* Count the number of entries needed */
> 

Comment in patch 1, but for the rest.

Reviewed-by: Bjorn Andersson <andersson@kernel.org>

Regards,
Bjorn

> Changelog v2:
> - dropped outdated patches (only 9 years passed :-)
> - rebased on top of the current kernel
> - left API SG wide It might
> 
> v1: https://patchwork.kernel.org/project/linux-dmaengine/patch/20161021173535.100245-1-andriy.shevchenko@linux.intel.com/
> 
> Andy Shevchenko (13):
>   scatterlist: introduce sg_nents_for_dma() helper
>   dmaengine: altera-msgdma: use sg_nents_for_dma() helper
>   dmaengine: axi-dmac: use sg_nents_for_dma() helper
>   dmaengine: bcm2835-dma: use sg_nents_for_dma() helper
>   dmaengine: dw-axi-dmac: use sg_nents_for_dma() helper
>   dmaengine: k3dma: use sg_nents_for_dma() helper
>   dmaengine: lgm: use sg_nents_for_dma() helper
>   dmaengine: pxa-dma: use sg_nents_for_dma() helper
>   dmaengine: qcom: adm: use sg_nents_for_dma() helper
>   dmaengine: qcom: bam_dma: use sg_nents_for_dma() helper
>   dmaengine: sa11x0: use sg_nents_for_dma() helper
>   dmaengine: sh: use sg_nents_for_dma() helper
>   dmaengine: xilinx: xdma: use sg_nents_for_dma() helper
> 
>  drivers/dma/altera-msgdma.c                   |  5 ++--
>  drivers/dma/bcm2835-dma.c                     | 19 +-------------
>  drivers/dma/dma-axi-dmac.c                    |  5 +---
>  .../dma/dw-axi-dmac/dw-axi-dmac-platform.c    |  6 ++---
>  drivers/dma/k3dma.c                           |  9 ++-----
>  drivers/dma/lgm/lgm-dma.c                     |  9 ++-----
>  drivers/dma/pxa_dma.c                         |  5 ++--
>  drivers/dma/qcom/bam_dma.c                    |  9 ++-----
>  drivers/dma/qcom/qcom_adm.c                   |  9 +++----
>  drivers/dma/sa11x0-dma.c                      |  6 ++---
>  drivers/dma/sh/shdma-base.c                   |  5 ++--
>  drivers/dma/xilinx/xdma.c                     |  6 ++---
>  include/linux/scatterlist.h                   |  2 ++
>  lib/scatterlist.c                             | 25 +++++++++++++++++++
>  14 files changed, 51 insertions(+), 69 deletions(-)
> 
> -- 
> 2.50.1
> 
>