[PATCH V3] dmaengine: imx-sdma: Fix SPBA bus detection on multi-SPBA platforms

[Shengjiu Wang]

On Tue, Apr 21, 2026 at 5:44 PM Marco Felsch <m.felsch at pengutronix.de> wrote:
>
> On 26-04-21, Shengjiu Wang wrote:
> > On Tue, Apr 21, 2026 at 4:57 PM Marco Felsch <m.felsch at pengutronix.de> wrote:
> > >
> > > On 26-04-20, Shengjiu Wang wrote:
> > > > i.MX8M platforms have multiple SPBA buses under different AIPS buses.
> > > > The current code searches the entire device tree and returns the first
> > > > SPBA bus found, which may not be under the same AIPS bus as the SDMA
> > > > controller.
> > > >
> > > > This breaks SDMA P2P transfers because the SDMA script needs to know
> > > > if peripherals are on SPBA or AIPS to configure watermark levels
> > > > correctly. Using the wrong SPBA bus causes DMA timeouts and transfer
> > > > failures.
> > > >
> > > > Fix by searching for the SPBA bus under the SDMA's parent node (AIPS)
> > > > first, then falling back to a global search for backward compatibility.
> > > >
> > > > Example device tree showing the issue:
> > > >   aips1 {
> > > >     spba1 { sai at ...; };      /* Correct SPBA for sdma1 */
> > > >     sdma1 at ...;
> > > >   };
> > > >   aips2 {
> > > >     spba2 { uart at ...; };     /* Wrong SPBA - found first by old code */
> > > >   };
> > > >
> > > > Fixes: 8391ecf465ec ("dmaengine: imx-sdma: Add device to device support")
> > > > Cc: stable at vger.kernel.org
> > > > Signed-off-by: Shengjiu Wang <shengjiu.wang at nxp.com>
> > > > ---
> > > > changs in v3:
> > > > - add fallback to a global search for backward compatibility, which is
> > > >   to address comments from sashiko.dev
> > > > - update commit subject and commit message
> > > > - add comments in code.
> > > > - add Cc stable tag
> > > > - Don't add Frank's RB on v2 as there are several other changes.
> > > >
> > > > changes in v2:
> > > > - add fixes tag
> > > > - use __free(device_node) for auto release.
> > > >
> > > >  drivers/dma/imx-sdma.c | 13 ++++++++++++-
> > > >  1 file changed, 12 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/drivers/dma/imx-sdma.c b/drivers/dma/imx-sdma.c
> > > > index 3d527883776b..592705af2319 100644
> > > > --- a/drivers/dma/imx-sdma.c
> > > > +++ b/drivers/dma/imx-sdma.c
> > > > @@ -2364,7 +2364,18 @@ static int sdma_probe(struct platform_device *pdev)
> > > >                       return dev_err_probe(&pdev->dev, ret,
> > > >                                            "failed to register controller\n");
> > > >
> > > > -             spba_bus = of_find_compatible_node(NULL, NULL, "fsl,spba-bus");
> > > > +             /*
> > > > +              * On i.MX8M platforms with multiple SPBA buses, we need to find
> > > > +              * the SPBA bus that's under the same AIPS bus as this SDMA controller.
> > > > +              * First check the SDMA's parent (AIPS bus) for a child SPBA bus.
> > > > +              * If not found, fall back to searching the entire device tree for
> > > > +              * backward compatibility with older platforms.
> > > > +              */
> > > > +             struct device_node *sdma_parent_np __free(device_node) = of_get_parent(np);
> > > > +
> > > > +             spba_bus = of_get_compatible_child(sdma_parent_np, "fsl,spba-bus");
> > > > +             if (!spba_bus)
> > > > +                     spba_bus = of_find_compatible_node(NULL, NULL, "fsl,spba-bus");
> > >
> > > And yet the search is still broken for i.MX8MP case since this platform
> > > has two sdma engines below the bus at 30df0000.
> >
> > I tested on i.MX8MP. It works.  Above line is for backward compatibility
> >
> > The search has no dependence on the number of sdma engines. It searches the
> > spba-bus, not the sdma node. it will find the aips5 first, then find
> > the spba-bus for
> > sdma2 and sdma3.
>
> And you're abosulte certain that NXP doesn't introduce a 2nd SPBA bus
> below the same AIPS in which case the driver is broken again?

Good question. Currently there are no two SPBA buses in the same AIPS
for all existing i.MX platforms and there is no such plan in the
current roadmap,
SDMA is replaced by EDMA from i.MX9.

>
> Sorry for beeing a bit picky. I do see that NXP decided to drop the SDMA
> for i.MX9, at least I don't find any reference in which case I'm fine
> with the patch.

Thanks.  The change should be safe.

Best regards
Shengjiu Wang