Re: [PATCH v3 2/9] dmaengine: dma-axi-dmac: Use bus width capability helpers

[nuno.sa@analog.com]

On Mon, Aug 31, 2026 at 12:01:11PM +0000, sashiko-bot@kernel.org wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [Medium] The legacy `src_addr_widths` and `dst_addr_widths` fields in `struct dma_device` are left uninitialized (0), breaking bisection for unconverted dmaengine consumers and directly contradicting the commit message.
> --
> 
> commit e0d3ea2099710250e81c32b95cc62ac180daeb2f
> Author: Nuno Sá <nuno.sa@analog.com>
> 
> dmaengine: dma-axi-dmac: Use bus width capability helpers
> 
> Advertise the source and destination bus widths through the new
> dma_set_{src,dst}_bus_width() helpers instead of open-coding the legacy
> BIT() mask.
> 
> > diff --git a/drivers/dma/dma-axi-dmac.c b/drivers/dma/dma-axi-dmac.c
> > index d47ff27e1408f..dc56178cafe08 100644
> > --- a/drivers/dma/dma-axi-dmac.c
> > +++ b/drivers/dma/dma-axi-dmac.c
> [ ... ]
> > @@ -1262,8 +1263,13 @@ static int axi_dmac_probe(struct platform_device *pdev)
> >  	dma_dev->device_terminate_all = axi_dmac_terminate_all;
> >  	dma_dev->device_synchronize = axi_dmac_synchronize;
> >  	dma_dev->dev = &pdev->dev;
> > -	dma_dev->src_addr_widths = BIT(dmac->chan.src_width);
> > -	dma_dev->dst_addr_widths = BIT(dmac->chan.dest_width);
> > +	ret = dma_bus_width_set(dma_dev->src_bus_widths, dmac->chan.src_width);
> > +	if (ret)
> > +		return ret;
> > +
> > +	ret = dma_bus_width_set(dma_dev->dst_bus_widths, dmac->chan.dest_width);
> > +	if (ret)
> > +		return ret;
> 
> [Severity: Medium]
> Will this break bisection for unconverted dmaengine consumers by leaving the
> legacy src_addr_widths and dst_addr_widths uninitialized?
> 
> The commit message states the intent is "keeping the legacy u32 fields
> populated during the transition."
> 
> However, this patch removes the assignments to dma_dev->src_addr_widths and
> dma_dev->dst_addr_widths and replaces them with dma_bus_width_set(), which only
> populates the new bitmap masks.
> 
> The DMA engine core's fallback logic in dma_get_slave_caps() (which folds the
> new bitmaps into the legacy caps fields) is placed inside an if
> (device->device_caps) block. Because axi-dmac does not implement a
> device_caps() callback, this fallback is never executed.
> 

Oh yeah! sashiko seems to have a point!!

> Consequently, will unconverted legacy consumers (like IIO) querying channel
> capabilities during bisection receive caps->src_addr_widths == 0, causing DMA
> transfer configurations to fail?
> 
> While this regression is fixed later in the patch series (when legacy fields
> are dropped and consumers are fully converted), it seems to cause a bisection
> breakage in the intermediate patches.
> 
> Could the legacy assignments be retained alongside the new helper calls to
> match the commit message's stated intent?
> 
> -- 
> Sashiko AI review · https://sashiko.dev/#/patchset/20260831-dmaengine-support-wider-dma-masks-v3-0-507d97496f2d@analog.com?part=2