RE: [PATCH] spi: rspi: Fix DMA mode when the DMA controller is built as a module

[Ovidiu Panait]

Hi Geert,

> 
> Hi Ovidiu,
> 
> On Mon, 21 Sept 2026 at 22:00, Ovidiu Panait
> <ovidiu.panait.rb@xxxxxxxxxxx> wrote:
> > On the Renesas RZ/G2L platform, the RSPI driver falls back to PIO mode
> > instead of using DMA when the DMA controller driver is built as a module
> > (CONFIG_RZ_DMAC=m):
> >
> >     renesas_spi 1004b000.spi: dma_request_slave_channel_compat failed
> >     renesas_spi 1004b000.spi: DMA not available, using PIO
> >
> > The driver requests DMA channels through
> dma_request_slave_channel_compat()
> > which returns either a valid pointer or NULL and cannot handle
> > -EPROBE_DEFER. If the DMA controller has not probed yet, the driver
> falls
> > back to PIO directly.
> >
> > Fix this by replacing the dma_request_slave_channel_compat() call with a
> > regular dma_request_chan() call. dma_request_slave_channel_compat() is
> > always passed a NULL fn_param in all code paths, so it actually behaves
> > like a plain dma_request_chan() call.
> >
> > Fixes: e825b8dd2b36 ("spi: rspi: Add DT support to DMA setup")
> > Signed-off-by: Ovidiu Panait <ovidiu.panait.rb@xxxxxxxxxxx>
> 
> Thanks for your patch!
> 
> > --- a/drivers/spi/spi-rspi.c
> > +++ b/drivers/spi/spi-rspi.c
> > @@ -1355,6 +1339,11 @@ static int rspi_probe(struct platform_device
> *pdev)
> >         }
> >
> >         ret = rspi_request_dma(&pdev->dev, ctlr, res);
> > +       if (ret == -EPROBE_DEFER) {
> > +               dev_err_probe(&pdev->dev, ret,
> > +                             "failed to request DMA channels\n");
> > +               goto error2;
> 
> Doesn't this make the probe fail if the DMA driver is not available
> at all?
> 

Yes, if the "dmas" property is present but the DMA driver is not available
at all, the probe will keep deferring. This matches other drivers I checked
(spi-rzv2h-rspi, spi-rockchip, spi-bcm2835, etc).

> > +       }
> >         if (ret < 0)
> >                 dev_warn(&pdev->dev, "DMA not available, using PIO\n");
> 
> The driver still falls back to PIO in case of a missing "dmas"
> property, right?
> 

Yes, without "dmas", the driver still falls back to PIO.

Thanks,
Ovidiu

> Gr{oetje,eeting}s,
> 
>                         Geert
> 
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-
> m68k.org
> 
> In personal conversations with technical people, I call myself a hacker.
> But
> when I'm talking to journalists I just say "programmer" or something like
> that.
>                                 -- Linus Torvalds