[PATCH v2 1/1] dmaengine: at_xdmac: fix transfer data width in at_xdmac_prep_slave_sg()

[PATCH v2 1/1] dmaengine: at_xdmac: fix transfer data width in at_xdmac_prep_slave_sg()

[Cyrille Pitchen]

This patch adds the missing update of the transfer data width in
at_xdmac_prep_slave_sg().

Indeed, for each item in the scatter-gather list, we check whether the
transfer length is aligned with the data width provided by
dmaengine_slave_config(). If so, we directly use this data width for the
current part of the transfer we are preparing. Otherwise, the data width
is reduced to 8 bits (1 byte). Of course, the actual number of register
accesses must also be updated to match the new data width.

So one chunk was missing in the original patch (see Fixes tag below): the
number of register accesses was correctly set to (len >> fixed_dwidth) in
mbr_ubc but the real data width was not updated in mbr_cfg. Since mbr_cfg
may change for each part of the scatter-gather transfer this also explains
why the original patch used the Descriptor View 2 instead of the
Descriptor View 1.

Let's take the example of a DMA transfer to write 8bit data into an Atmel
USART with FIFOs. When FIFOs are enabled in the USART, its Transmit
Holding Register (THR) works in multidata mode, that is to say that up to
4 8bit data can be written into the THR in a single 32bit access and it is
still possible to write only one data with a 8bit access. To take
advantage of this new feature, the DMA driver was modified to allow
multiple dwidths when doing slave transfers.
For instance, when the total length is 22 bytes, the USART driver splits
the transfer into 2 parts:

First part: 20 bytes transferred through 5 32bit writes into THR
Second part: 2 bytes transferred though 2 8bit writes into THR

For the second part, the data width was first set to 4_BYTES by the USART
driver thanks to dmaengine_slave_config() then at_xdmac_prep_slave_sg()
reduces this data width to 1_BYTE because the 2 byte length is not aligned
with the original 4_BYTES data width. Since the data width is modified,
the actual number of writes into THR must be set accordingly.

Signed-off-by: Cyrille Pitchen <cyrille.pitchen@atmel.com>
Fixes: 6d3a7d9e3ada ("dmaengine: at_xdmac: allow muliple dwidths when doing slave transfers")
Cc: stable@vger.kernel.org #4.0 and later
---
ChangeLog

v2:
- reword commit message: add Fixes and Cc tags

v1:

 drivers/dma/at_xdmac.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/dma/at_xdmac.c b/drivers/dma/at_xdmac.c
index cf1213de7865..931b2183e2a7 100644
--- a/drivers/dma/at_xdmac.c
+++ b/drivers/dma/at_xdmac.c
@@ -681,15 +681,16 @@ at_xdmac_prep_slave_sg(struct dma_chan *chan, struct scatterlist *sgl,
 			desc->lld.mbr_sa = mem;
 			desc->lld.mbr_da = atchan->sconfig.dst_addr;
 		}
-		desc->lld.mbr_cfg = atchan->cfg;
-		dwidth = at_xdmac_get_dwidth(desc->lld.mbr_cfg);
+		dwidth = at_xdmac_get_dwidth(atchan->cfg);
 		fixed_dwidth = IS_ALIGNED(len, 1 << dwidth)
-			       ? at_xdmac_get_dwidth(desc->lld.mbr_cfg)
+			       ? dwidth
 			       : AT_XDMAC_CC_DWIDTH_BYTE;
 		desc->lld.mbr_ubc = AT_XDMAC_MBR_UBC_NDV2			/* next descriptor view */
 			| AT_XDMAC_MBR_UBC_NDEN					/* next descriptor dst parameter update */
 			| AT_XDMAC_MBR_UBC_NSEN					/* next descriptor src parameter update */
 			| (len >> fixed_dwidth);				/* microblock length */
+		desc->lld.mbr_cfg = (atchan->cfg & ~AT_XDMAC_CC_DWIDTH_MASK) |
+				    AT_XDMAC_CC_DWIDTH(fixed_dwidth);
 		dev_dbg(chan2dev(chan),
 			 "%s: lld: mbr_sa=%pad, mbr_da=%pad, mbr_ubc=0x%08x\n",
 			 __func__, &desc->lld.mbr_sa, &desc->lld.mbr_da, desc->lld.mbr_ubc);
-- 
1.8.2.2

[PATCH v2 1/1] dmaengine: at_xdmac: fix transfer data width in at_xdmac_prep_slave_sg()

[Cyrille Pitchen]

This patch adds the missing update of the transfer data width in
at_xdmac_prep_slave_sg().

Indeed, for each item in the scatter-gather list, we check whether the
transfer length is aligned with the data width provided by
dmaengine_slave_config(). If so, we directly use this data width for the
current part of the transfer we are preparing. Otherwise, the data width
is reduced to 8 bits (1 byte). Of course, the actual number of register
accesses must also be updated to match the new data width.

So one chunk was missing in the original patch (see Fixes tag below): the
number of register accesses was correctly set to (len >> fixed_dwidth) in
mbr_ubc but the real data width was not updated in mbr_cfg. Since mbr_cfg
may change for each part of the scatter-gather transfer this also explains
why the original patch used the Descriptor View 2 instead of the
Descriptor View 1.

Let's take the example of a DMA transfer to write 8bit data into an Atmel
USART with FIFOs. When FIFOs are enabled in the USART, its Transmit
Holding Register (THR) works in multidata mode, that is to say that up to
4 8bit data can be written into the THR in a single 32bit access and it is
still possible to write only one data with a 8bit access. To take
advantage of this new feature, the DMA driver was modified to allow
multiple dwidths when doing slave transfers.
For instance, when the total length is 22 bytes, the USART driver splits
the transfer into 2 parts:

First part: 20 bytes transferred through 5 32bit writes into THR
Second part: 2 bytes transferred though 2 8bit writes into THR

For the second part, the data width was first set to 4_BYTES by the USART
driver thanks to dmaengine_slave_config() then at_xdmac_prep_slave_sg()
reduces this data width to 1_BYTE because the 2 byte length is not aligned
with the original 4_BYTES data width. Since the data width is modified,
the actual number of writes into THR must be set accordingly.

Signed-off-by: Cyrille Pitchen <cyrille.pitchen@atmel.com>
Fixes: 6d3a7d9e3ada ("dmaengine: at_xdmac: allow muliple dwidths when doing slave transfers")
Cc: stable at vger.kernel.org #4.0 and later
---
ChangeLog

v2:
- reword commit message: add Fixes and Cc tags

v1:

 drivers/dma/at_xdmac.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/dma/at_xdmac.c b/drivers/dma/at_xdmac.c
index cf1213de7865..931b2183e2a7 100644
--- a/drivers/dma/at_xdmac.c
+++ b/drivers/dma/at_xdmac.c
@@ -681,15 +681,16 @@ at_xdmac_prep_slave_sg(struct dma_chan *chan, struct scatterlist *sgl,
 			desc->lld.mbr_sa = mem;
 			desc->lld.mbr_da = atchan->sconfig.dst_addr;
 		}
-		desc->lld.mbr_cfg = atchan->cfg;
-		dwidth = at_xdmac_get_dwidth(desc->lld.mbr_cfg);
+		dwidth = at_xdmac_get_dwidth(atchan->cfg);
 		fixed_dwidth = IS_ALIGNED(len, 1 << dwidth)
-			       ? at_xdmac_get_dwidth(desc->lld.mbr_cfg)
+			       ? dwidth
 			       : AT_XDMAC_CC_DWIDTH_BYTE;
 		desc->lld.mbr_ubc = AT_XDMAC_MBR_UBC_NDV2			/* next descriptor view */
 			| AT_XDMAC_MBR_UBC_NDEN					/* next descriptor dst parameter update */
 			| AT_XDMAC_MBR_UBC_NSEN					/* next descriptor src parameter update */
 			| (len >> fixed_dwidth);				/* microblock length */
+		desc->lld.mbr_cfg = (atchan->cfg & ~AT_XDMAC_CC_DWIDTH_MASK) |
+				    AT_XDMAC_CC_DWIDTH(fixed_dwidth);
 		dev_dbg(chan2dev(chan),
 			 "%s: lld: mbr_sa=%pad, mbr_da=%pad, mbr_ubc=0x%08x\n",
 			 __func__, &desc->lld.mbr_sa, &desc->lld.mbr_da, desc->lld.mbr_ubc);
-- 
1.8.2.2

Re: [PATCH v2 1/1] dmaengine: at_xdmac: fix transfer data width in at_xdmac_prep_slave_sg()

[Nicolas Ferre]

Le 30/06/2015 14:36, Cyrille Pitchen a écrit :
> This patch adds the missing update of the transfer data width in
> at_xdmac_prep_slave_sg().
> 
> Indeed, for each item in the scatter-gather list, we check whether the
> transfer length is aligned with the data width provided by
> dmaengine_slave_config(). If so, we directly use this data width for the
> current part of the transfer we are preparing. Otherwise, the data width
> is reduced to 8 bits (1 byte). Of course, the actual number of register
> accesses must also be updated to match the new data width.
> 
> So one chunk was missing in the original patch (see Fixes tag below): the
> number of register accesses was correctly set to (len >> fixed_dwidth) in
> mbr_ubc but the real data width was not updated in mbr_cfg. Since mbr_cfg
> may change for each part of the scatter-gather transfer this also explains
> why the original patch used the Descriptor View 2 instead of the
> Descriptor View 1.
> 
> Let's take the example of a DMA transfer to write 8bit data into an Atmel
> USART with FIFOs. When FIFOs are enabled in the USART, its Transmit
> Holding Register (THR) works in multidata mode, that is to say that up to
> 4 8bit data can be written into the THR in a single 32bit access and it is
> still possible to write only one data with a 8bit access. To take
> advantage of this new feature, the DMA driver was modified to allow
> multiple dwidths when doing slave transfers.
> For instance, when the total length is 22 bytes, the USART driver splits
> the transfer into 2 parts:
> 
> First part: 20 bytes transferred through 5 32bit writes into THR
> Second part: 2 bytes transferred though 2 8bit writes into THR
> 
> For the second part, the data width was first set to 4_BYTES by the USART
> driver thanks to dmaengine_slave_config() then at_xdmac_prep_slave_sg()
> reduces this data width to 1_BYTE because the 2 byte length is not aligned
> with the original 4_BYTES data width. Since the data width is modified,
> the actual number of writes into THR must be set accordingly.
> 
> Signed-off-by: Cyrille Pitchen <cyrille.pitchen@atmel.com>
> Fixes: 6d3a7d9e3ada ("dmaengine: at_xdmac: allow muliple dwidths when doing slave transfers")
> Cc: stable@vger.kernel.org #4.0 and later

Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>

> ---
> ChangeLog
> 
> v2:
> - reword commit message: add Fixes and Cc tags
> 
> v1:
> 
>  drivers/dma/at_xdmac.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/dma/at_xdmac.c b/drivers/dma/at_xdmac.c
> index cf1213de7865..931b2183e2a7 100644
> --- a/drivers/dma/at_xdmac.c
> +++ b/drivers/dma/at_xdmac.c
> @@ -681,15 +681,16 @@ at_xdmac_prep_slave_sg(struct dma_chan *chan, struct scatterlist *sgl,
>  			desc->lld.mbr_sa = mem;
>  			desc->lld.mbr_da = atchan->sconfig.dst_addr;
>  		}
> -		desc->lld.mbr_cfg = atchan->cfg;
> -		dwidth = at_xdmac_get_dwidth(desc->lld.mbr_cfg);
> +		dwidth = at_xdmac_get_dwidth(atchan->cfg);
>  		fixed_dwidth = IS_ALIGNED(len, 1 << dwidth)
> -			       ? at_xdmac_get_dwidth(desc->lld.mbr_cfg)
> +			       ? dwidth
>  			       : AT_XDMAC_CC_DWIDTH_BYTE;
>  		desc->lld.mbr_ubc = AT_XDMAC_MBR_UBC_NDV2			/* next descriptor view */
>  			| AT_XDMAC_MBR_UBC_NDEN					/* next descriptor dst parameter update */
>  			| AT_XDMAC_MBR_UBC_NSEN					/* next descriptor src parameter update */
>  			| (len >> fixed_dwidth);				/* microblock length */
> +		desc->lld.mbr_cfg = (atchan->cfg & ~AT_XDMAC_CC_DWIDTH_MASK) |
> +				    AT_XDMAC_CC_DWIDTH(fixed_dwidth);
>  		dev_dbg(chan2dev(chan),
>  			 "%s: lld: mbr_sa=%pad, mbr_da=%pad, mbr_ubc=0x%08x\n",
>  			 __func__, &desc->lld.mbr_sa, &desc->lld.mbr_da, desc->lld.mbr_ubc);
> 


-- 
Nicolas Ferre

[PATCH v2 1/1] dmaengine: at_xdmac: fix transfer data width in at_xdmac_prep_slave_sg()

[Nicolas Ferre]

Le 30/06/2015 14:36, Cyrille Pitchen a ?crit :
> This patch adds the missing update of the transfer data width in
> at_xdmac_prep_slave_sg().
> 
> Indeed, for each item in the scatter-gather list, we check whether the
> transfer length is aligned with the data width provided by
> dmaengine_slave_config(). If so, we directly use this data width for the
> current part of the transfer we are preparing. Otherwise, the data width
> is reduced to 8 bits (1 byte). Of course, the actual number of register
> accesses must also be updated to match the new data width.
> 
> So one chunk was missing in the original patch (see Fixes tag below): the
> number of register accesses was correctly set to (len >> fixed_dwidth) in
> mbr_ubc but the real data width was not updated in mbr_cfg. Since mbr_cfg
> may change for each part of the scatter-gather transfer this also explains
> why the original patch used the Descriptor View 2 instead of the
> Descriptor View 1.
> 
> Let's take the example of a DMA transfer to write 8bit data into an Atmel
> USART with FIFOs. When FIFOs are enabled in the USART, its Transmit
> Holding Register (THR) works in multidata mode, that is to say that up to
> 4 8bit data can be written into the THR in a single 32bit access and it is
> still possible to write only one data with a 8bit access. To take
> advantage of this new feature, the DMA driver was modified to allow
> multiple dwidths when doing slave transfers.
> For instance, when the total length is 22 bytes, the USART driver splits
> the transfer into 2 parts:
> 
> First part: 20 bytes transferred through 5 32bit writes into THR
> Second part: 2 bytes transferred though 2 8bit writes into THR
> 
> For the second part, the data width was first set to 4_BYTES by the USART
> driver thanks to dmaengine_slave_config() then at_xdmac_prep_slave_sg()
> reduces this data width to 1_BYTE because the 2 byte length is not aligned
> with the original 4_BYTES data width. Since the data width is modified,
> the actual number of writes into THR must be set accordingly.
> 
> Signed-off-by: Cyrille Pitchen <cyrille.pitchen@atmel.com>
> Fixes: 6d3a7d9e3ada ("dmaengine: at_xdmac: allow muliple dwidths when doing slave transfers")
> Cc: stable at vger.kernel.org #4.0 and later

Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>

> ---
> ChangeLog
> 
> v2:
> - reword commit message: add Fixes and Cc tags
> 
> v1:
> 
>  drivers/dma/at_xdmac.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/dma/at_xdmac.c b/drivers/dma/at_xdmac.c
> index cf1213de7865..931b2183e2a7 100644
> --- a/drivers/dma/at_xdmac.c
> +++ b/drivers/dma/at_xdmac.c
> @@ -681,15 +681,16 @@ at_xdmac_prep_slave_sg(struct dma_chan *chan, struct scatterlist *sgl,
>  			desc->lld.mbr_sa = mem;
>  			desc->lld.mbr_da = atchan->sconfig.dst_addr;
>  		}
> -		desc->lld.mbr_cfg = atchan->cfg;
> -		dwidth = at_xdmac_get_dwidth(desc->lld.mbr_cfg);
> +		dwidth = at_xdmac_get_dwidth(atchan->cfg);
>  		fixed_dwidth = IS_ALIGNED(len, 1 << dwidth)
> -			       ? at_xdmac_get_dwidth(desc->lld.mbr_cfg)
> +			       ? dwidth
>  			       : AT_XDMAC_CC_DWIDTH_BYTE;
>  		desc->lld.mbr_ubc = AT_XDMAC_MBR_UBC_NDV2			/* next descriptor view */
>  			| AT_XDMAC_MBR_UBC_NDEN					/* next descriptor dst parameter update */
>  			| AT_XDMAC_MBR_UBC_NSEN					/* next descriptor src parameter update */
>  			| (len >> fixed_dwidth);				/* microblock length */
> +		desc->lld.mbr_cfg = (atchan->cfg & ~AT_XDMAC_CC_DWIDTH_MASK) |
> +				    AT_XDMAC_CC_DWIDTH(fixed_dwidth);
>  		dev_dbg(chan2dev(chan),
>  			 "%s: lld: mbr_sa=%pad, mbr_da=%pad, mbr_ubc=0x%08x\n",
>  			 __func__, &desc->lld.mbr_sa, &desc->lld.mbr_da, desc->lld.mbr_ubc);
> 


-- 
Nicolas Ferre

Re: [PATCH v2 1/1] dmaengine: at_xdmac: fix transfer data width in at_xdmac_prep_slave_sg()

[Ludovic Desroches]

On Tue, Jun 30, 2015 at 02:36:57PM +0200, Cyrille Pitchen wrote:
> This patch adds the missing update of the transfer data width in
> at_xdmac_prep_slave_sg().
> 
> Indeed, for each item in the scatter-gather list, we check whether the
> transfer length is aligned with the data width provided by
> dmaengine_slave_config(). If so, we directly use this data width for the
> current part of the transfer we are preparing. Otherwise, the data width
> is reduced to 8 bits (1 byte). Of course, the actual number of register
> accesses must also be updated to match the new data width.
> 
> So one chunk was missing in the original patch (see Fixes tag below): the
> number of register accesses was correctly set to (len >> fixed_dwidth) in
> mbr_ubc but the real data width was not updated in mbr_cfg. Since mbr_cfg
> may change for each part of the scatter-gather transfer this also explains
> why the original patch used the Descriptor View 2 instead of the
> Descriptor View 1.
> 
> Let's take the example of a DMA transfer to write 8bit data into an Atmel
> USART with FIFOs. When FIFOs are enabled in the USART, its Transmit
> Holding Register (THR) works in multidata mode, that is to say that up to
> 4 8bit data can be written into the THR in a single 32bit access and it is
> still possible to write only one data with a 8bit access. To take
> advantage of this new feature, the DMA driver was modified to allow
> multiple dwidths when doing slave transfers.
> For instance, when the total length is 22 bytes, the USART driver splits
> the transfer into 2 parts:
> 
> First part: 20 bytes transferred through 5 32bit writes into THR
> Second part: 2 bytes transferred though 2 8bit writes into THR
> 
> For the second part, the data width was first set to 4_BYTES by the USART
> driver thanks to dmaengine_slave_config() then at_xdmac_prep_slave_sg()
> reduces this data width to 1_BYTE because the 2 byte length is not aligned
> with the original 4_BYTES data width. Since the data width is modified,
> the actual number of writes into THR must be set accordingly.
> 
> Signed-off-by: Cyrille Pitchen <cyrille.pitchen@atmel.com>

Acked-by: Ludovic Desroches <ludovic.desroches@atmel.com>

Thanks Cyrille

> Fixes: 6d3a7d9e3ada ("dmaengine: at_xdmac: allow muliple dwidths when doing slave transfers")
> Cc: stable@vger.kernel.org #4.0 and later
> ---
> ChangeLog
> 
> v2:
> - reword commit message: add Fixes and Cc tags
> 
> v1:
> 
>  drivers/dma/at_xdmac.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/dma/at_xdmac.c b/drivers/dma/at_xdmac.c
> index cf1213de7865..931b2183e2a7 100644
> --- a/drivers/dma/at_xdmac.c
> +++ b/drivers/dma/at_xdmac.c
> @@ -681,15 +681,16 @@ at_xdmac_prep_slave_sg(struct dma_chan *chan, struct scatterlist *sgl,
>  			desc->lld.mbr_sa = mem;
>  			desc->lld.mbr_da = atchan->sconfig.dst_addr;
>  		}
> -		desc->lld.mbr_cfg = atchan->cfg;
> -		dwidth = at_xdmac_get_dwidth(desc->lld.mbr_cfg);
> +		dwidth = at_xdmac_get_dwidth(atchan->cfg);
>  		fixed_dwidth = IS_ALIGNED(len, 1 << dwidth)
> -			       ? at_xdmac_get_dwidth(desc->lld.mbr_cfg)
> +			       ? dwidth
>  			       : AT_XDMAC_CC_DWIDTH_BYTE;
>  		desc->lld.mbr_ubc = AT_XDMAC_MBR_UBC_NDV2			/* next descriptor view */
>  			| AT_XDMAC_MBR_UBC_NDEN					/* next descriptor dst parameter update */
>  			| AT_XDMAC_MBR_UBC_NSEN					/* next descriptor src parameter update */
>  			| (len >> fixed_dwidth);				/* microblock length */
> +		desc->lld.mbr_cfg = (atchan->cfg & ~AT_XDMAC_CC_DWIDTH_MASK) |
> +				    AT_XDMAC_CC_DWIDTH(fixed_dwidth);
>  		dev_dbg(chan2dev(chan),
>  			 "%s: lld: mbr_sa=%pad, mbr_da=%pad, mbr_ubc=0x%08x\n",
>  			 __func__, &desc->lld.mbr_sa, &desc->lld.mbr_da, desc->lld.mbr_ubc);
> -- 
> 1.8.2.2
> 

[PATCH v2 1/1] dmaengine: at_xdmac: fix transfer data width in at_xdmac_prep_slave_sg()

[Ludovic Desroches]

On Tue, Jun 30, 2015 at 02:36:57PM +0200, Cyrille Pitchen wrote:
> This patch adds the missing update of the transfer data width in
> at_xdmac_prep_slave_sg().
> 
> Indeed, for each item in the scatter-gather list, we check whether the
> transfer length is aligned with the data width provided by
> dmaengine_slave_config(). If so, we directly use this data width for the
> current part of the transfer we are preparing. Otherwise, the data width
> is reduced to 8 bits (1 byte). Of course, the actual number of register
> accesses must also be updated to match the new data width.
> 
> So one chunk was missing in the original patch (see Fixes tag below): the
> number of register accesses was correctly set to (len >> fixed_dwidth) in
> mbr_ubc but the real data width was not updated in mbr_cfg. Since mbr_cfg
> may change for each part of the scatter-gather transfer this also explains
> why the original patch used the Descriptor View 2 instead of the
> Descriptor View 1.
> 
> Let's take the example of a DMA transfer to write 8bit data into an Atmel
> USART with FIFOs. When FIFOs are enabled in the USART, its Transmit
> Holding Register (THR) works in multidata mode, that is to say that up to
> 4 8bit data can be written into the THR in a single 32bit access and it is
> still possible to write only one data with a 8bit access. To take
> advantage of this new feature, the DMA driver was modified to allow
> multiple dwidths when doing slave transfers.
> For instance, when the total length is 22 bytes, the USART driver splits
> the transfer into 2 parts:
> 
> First part: 20 bytes transferred through 5 32bit writes into THR
> Second part: 2 bytes transferred though 2 8bit writes into THR
> 
> For the second part, the data width was first set to 4_BYTES by the USART
> driver thanks to dmaengine_slave_config() then at_xdmac_prep_slave_sg()
> reduces this data width to 1_BYTE because the 2 byte length is not aligned
> with the original 4_BYTES data width. Since the data width is modified,
> the actual number of writes into THR must be set accordingly.
> 
> Signed-off-by: Cyrille Pitchen <cyrille.pitchen@atmel.com>

Acked-by: Ludovic Desroches <ludovic.desroches@atmel.com>

Thanks Cyrille

> Fixes: 6d3a7d9e3ada ("dmaengine: at_xdmac: allow muliple dwidths when doing slave transfers")
> Cc: stable at vger.kernel.org #4.0 and later
> ---
> ChangeLog
> 
> v2:
> - reword commit message: add Fixes and Cc tags
> 
> v1:
> 
>  drivers/dma/at_xdmac.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/dma/at_xdmac.c b/drivers/dma/at_xdmac.c
> index cf1213de7865..931b2183e2a7 100644
> --- a/drivers/dma/at_xdmac.c
> +++ b/drivers/dma/at_xdmac.c
> @@ -681,15 +681,16 @@ at_xdmac_prep_slave_sg(struct dma_chan *chan, struct scatterlist *sgl,
>  			desc->lld.mbr_sa = mem;
>  			desc->lld.mbr_da = atchan->sconfig.dst_addr;
>  		}
> -		desc->lld.mbr_cfg = atchan->cfg;
> -		dwidth = at_xdmac_get_dwidth(desc->lld.mbr_cfg);
> +		dwidth = at_xdmac_get_dwidth(atchan->cfg);
>  		fixed_dwidth = IS_ALIGNED(len, 1 << dwidth)
> -			       ? at_xdmac_get_dwidth(desc->lld.mbr_cfg)
> +			       ? dwidth
>  			       : AT_XDMAC_CC_DWIDTH_BYTE;
>  		desc->lld.mbr_ubc = AT_XDMAC_MBR_UBC_NDV2			/* next descriptor view */
>  			| AT_XDMAC_MBR_UBC_NDEN					/* next descriptor dst parameter update */
>  			| AT_XDMAC_MBR_UBC_NSEN					/* next descriptor src parameter update */
>  			| (len >> fixed_dwidth);				/* microblock length */
> +		desc->lld.mbr_cfg = (atchan->cfg & ~AT_XDMAC_CC_DWIDTH_MASK) |
> +				    AT_XDMAC_CC_DWIDTH(fixed_dwidth);
>  		dev_dbg(chan2dev(chan),
>  			 "%s: lld: mbr_sa=%pad, mbr_da=%pad, mbr_ubc=0x%08x\n",
>  			 __func__, &desc->lld.mbr_sa, &desc->lld.mbr_da, desc->lld.mbr_ubc);
> -- 
> 1.8.2.2
> 

Re: [PATCH v2 1/1] dmaengine: at_xdmac: fix transfer data width in at_xdmac_prep_slave_sg()

[Vinod Koul]

On Tue, Jun 30, 2015 at 02:36:57PM +0200, Cyrille Pitchen wrote:
> This patch adds the missing update of the transfer data width in
> at_xdmac_prep_slave_sg().
> 
> Indeed, for each item in the scatter-gather list, we check whether the
> transfer length is aligned with the data width provided by
> dmaengine_slave_config(). If so, we directly use this data width for the
> current part of the transfer we are preparing. Otherwise, the data width
> is reduced to 8 bits (1 byte). Of course, the actual number of register
> accesses must also be updated to match the new data width.
> 
> So one chunk was missing in the original patch (see Fixes tag below): the
> number of register accesses was correctly set to (len >> fixed_dwidth) in
> mbr_ubc but the real data width was not updated in mbr_cfg. Since mbr_cfg
> may change for each part of the scatter-gather transfer this also explains
> why the original patch used the Descriptor View 2 instead of the
> Descriptor View 1.
> 
> Let's take the example of a DMA transfer to write 8bit data into an Atmel
> USART with FIFOs. When FIFOs are enabled in the USART, its Transmit
> Holding Register (THR) works in multidata mode, that is to say that up to
> 4 8bit data can be written into the THR in a single 32bit access and it is
> still possible to write only one data with a 8bit access. To take
> advantage of this new feature, the DMA driver was modified to allow
> multiple dwidths when doing slave transfers.
> For instance, when the total length is 22 bytes, the USART driver splits
> the transfer into 2 parts:
> 
> First part: 20 bytes transferred through 5 32bit writes into THR
> Second part: 2 bytes transferred though 2 8bit writes into THR
> 
> For the second part, the data width was first set to 4_BYTES by the USART
> driver thanks to dmaengine_slave_config() then at_xdmac_prep_slave_sg()
> reduces this data width to 1_BYTE because the 2 byte length is not aligned
> with the original 4_BYTES data width. Since the data width is modified,
> the actual number of writes into THR must be set accordingly.
 
Applied thanks

-- 
~Vinod

[PATCH v2 1/1] dmaengine: at_xdmac: fix transfer data width in at_xdmac_prep_slave_sg()

[Vinod Koul]

On Tue, Jun 30, 2015 at 02:36:57PM +0200, Cyrille Pitchen wrote:
> This patch adds the missing update of the transfer data width in
> at_xdmac_prep_slave_sg().
> 
> Indeed, for each item in the scatter-gather list, we check whether the
> transfer length is aligned with the data width provided by
> dmaengine_slave_config(). If so, we directly use this data width for the
> current part of the transfer we are preparing. Otherwise, the data width
> is reduced to 8 bits (1 byte). Of course, the actual number of register
> accesses must also be updated to match the new data width.
> 
> So one chunk was missing in the original patch (see Fixes tag below): the
> number of register accesses was correctly set to (len >> fixed_dwidth) in
> mbr_ubc but the real data width was not updated in mbr_cfg. Since mbr_cfg
> may change for each part of the scatter-gather transfer this also explains
> why the original patch used the Descriptor View 2 instead of the
> Descriptor View 1.
> 
> Let's take the example of a DMA transfer to write 8bit data into an Atmel
> USART with FIFOs. When FIFOs are enabled in the USART, its Transmit
> Holding Register (THR) works in multidata mode, that is to say that up to
> 4 8bit data can be written into the THR in a single 32bit access and it is
> still possible to write only one data with a 8bit access. To take
> advantage of this new feature, the DMA driver was modified to allow
> multiple dwidths when doing slave transfers.
> For instance, when the total length is 22 bytes, the USART driver splits
> the transfer into 2 parts:
> 
> First part: 20 bytes transferred through 5 32bit writes into THR
> Second part: 2 bytes transferred though 2 8bit writes into THR
> 
> For the second part, the data width was first set to 4_BYTES by the USART
> driver thanks to dmaengine_slave_config() then at_xdmac_prep_slave_sg()
> reduces this data width to 1_BYTE because the 2 byte length is not aligned
> with the original 4_BYTES data width. Since the data width is modified,
> the actual number of writes into THR must be set accordingly.
 
Applied thanks

-- 
~Vinod