Re: [PATCH v2 5/9] dmaengine: stm32-dma3: Use bus width capability helpers

["Nuno Sá" <nuno.sa@analog.com>]

On Fri, Aug 28, 2026 at 02:40:05PM +0200, Amelie Delaunay wrote:
> Hi Nuno,
> 
> Thanks for the update to the stm32-dma3 driver. It's good to see that it
> helps demonstrate the dma_slave_caps_clear_xxx API.
> 
> For future patches touching STM32-related drivers, please CC the linux-stm32
> mailing list, as this one went unnoticed on our side.
> 

Yes! You're right, sorry for that! The problem was that this started as
RFC as I just wanted to get opinions from the DMA folks on the way to go!
Then I forgot to include other reviewers (I missed more that ST folks)
on the following iterations.
Also found out an issue with my b4 workflow because of this :)

- Nuno Sá

> On 8/10/26 17:06, Nuno Sá wrote:
> > Advertise the controller-wide bus width capabilities through the new
> > dma_set_src_bus_widths() and dma_set_dst_bus_widths() helpers.
> > 
> > Also update the per-channel capability callback to clear unsupported
> > widths through the dma_slave_caps helpers so the bitmap and
> > transitional legacy fields stay in sync.
> > 
> > Reviewed-by: Frank Li <Frank.Li@nxp.com>
> > Signed-off-by: Nuno Sá <nuno.sa@analog.com>
> > ---
> >   drivers/dma/stm32/stm32-dma3.c | 32 ++++++++++++++++++++------------
> >   1 file changed, 20 insertions(+), 12 deletions(-)
> > 
> > diff --git a/drivers/dma/stm32/stm32-dma3.c b/drivers/dma/stm32/stm32-dma3.c
> > index 4724e7fa0008..f0781fb1b66f 100644
> > --- a/drivers/dma/stm32/stm32-dma3.c
> > +++ b/drivers/dma/stm32/stm32-dma3.c
> > @@ -1469,14 +1469,14 @@ static void stm32_dma3_caps(struct dma_chan *c, struct dma_slave_caps *caps)
> >   	if (!chan->fifo_size) {
> >   		caps->max_burst = 0;
> > -		caps->src_addr_widths &= ~BIT(DMA_SLAVE_BUSWIDTH_8_BYTES);
> > -		caps->dst_addr_widths &= ~BIT(DMA_SLAVE_BUSWIDTH_8_BYTES);
> > +		dma_slave_caps_clear_src_width(caps, DMA_SLAVE_BUSWIDTH_8_BYTES);
> > +		dma_slave_caps_clear_dst_width(caps, DMA_SLAVE_BUSWIDTH_8_BYTES);
> >   	} else {
> >   		/* Burst transfer should not exceed half of the fifo size */
> >   		caps->max_burst = chan->max_burst;
> >   		if (caps->max_burst < DMA_SLAVE_BUSWIDTH_8_BYTES) {
> > -			caps->src_addr_widths &= ~BIT(DMA_SLAVE_BUSWIDTH_8_BYTES);
> > -			caps->dst_addr_widths &= ~BIT(DMA_SLAVE_BUSWIDTH_8_BYTES);
> > +			dma_slave_caps_clear_src_width(caps, DMA_SLAVE_BUSWIDTH_8_BYTES);
> > +			dma_slave_caps_clear_dst_width(caps, DMA_SLAVE_BUSWIDTH_8_BYTES);
> >   		}
> >   	}
> >   }
> > @@ -1737,6 +1737,12 @@ static int stm32_dma3_probe(struct platform_device *pdev)
> >   	u32 master_ports, chan_reserved, i, verr;
> >   	u64 hwcfgr;
> >   	int ret;
> > +	enum dma_slave_buswidth stm32_dma3_buswidths[] = {
> > +		DMA_SLAVE_BUSWIDTH_1_BYTE,
> > +		DMA_SLAVE_BUSWIDTH_2_BYTES,
> > +		DMA_SLAVE_BUSWIDTH_4_BYTES,
> > +		DMA_SLAVE_BUSWIDTH_8_BYTES,
> > +	};
> 
> I'm not fond of having this large block after the "shortest" declaration
> (reversed christmas tree order), and since it is not a global variable, I
> think you can remove the `stm32_dma3` prefix.
> 
> By removing the `stm32_dma3` prefix, you could place it after the struct
> declarations, below struct dma_device *dma_dev;
> 
> >   	ddata = devm_kzalloc(&pdev->dev, sizeof(*ddata), GFP_KERNEL);
> >   	if (!ddata)
> > @@ -1775,14 +1781,16 @@ static int stm32_dma3_probe(struct platform_device *pdev)
> >   	 * channel, and can only access address at even boundaries, multiple of the buswidth.
> >   	 */
> >   	dma_dev->copy_align = DMAENGINE_ALIGN_8_BYTES;
> > -	dma_dev->src_addr_widths = BIT(DMA_SLAVE_BUSWIDTH_1_BYTE) |
> > -				   BIT(DMA_SLAVE_BUSWIDTH_2_BYTES) |
> > -				   BIT(DMA_SLAVE_BUSWIDTH_4_BYTES) |
> > -				   BIT(DMA_SLAVE_BUSWIDTH_8_BYTES);
> > -	dma_dev->dst_addr_widths = BIT(DMA_SLAVE_BUSWIDTH_1_BYTE) |
> > -				   BIT(DMA_SLAVE_BUSWIDTH_2_BYTES) |
> > -				   BIT(DMA_SLAVE_BUSWIDTH_4_BYTES) |
> > -				   BIT(DMA_SLAVE_BUSWIDTH_8_BYTES);
> > +	ret = dma_set_src_bus_widths(dma_dev, stm32_dma3_buswidths,
> > +				     ARRAY_SIZE(stm32_dma3_buswidths));
> 
> By using `buswidths` instead of `stm32_dma3_buswidths`, this can fit on a
> single line.
> 
> > +	if (ret)
> > +		goto err_clk_disable;
> > +
> > +	ret = dma_set_dst_bus_widths(dma_dev, stm32_dma3_buswidths,
> > +				     ARRAY_SIZE(stm32_dma3_buswidths));
> 
> Ditto
> 
> > +	if (ret)
> > +		goto err_clk_disable;
> > +
> >   	dma_dev->directions = BIT(DMA_DEV_TO_MEM) | BIT(DMA_MEM_TO_DEV) | BIT(DMA_MEM_TO_MEM);
> >   	dma_dev->descriptor_reuse = true;
> > 
> 
> Regards,
> Amelie