Re: [PATCH 3/3] dmaengine: sf-pdma: Get number of channel by device tree

[Zong Li]

On Mon, Jan 10, 2022 at 4:58 PM Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote:
>
> Hi Zong,
>
> On Wed, Jan 5, 2022 at 6:44 AM Zong Li <zong.li@xxxxxxxxxx> wrote:
> > It currently assumes that there are four channels by default, it might
> > cause the error if there is actually less than four channels. Change
> > that by getting number of channel from device tree.
> >
> > Signed-off-by: Zong Li <zong.li@xxxxxxxxxx>
>
> Thanks for your patch!
>
> > --- a/drivers/dma/sf-pdma/sf-pdma.c
> > +++ b/drivers/dma/sf-pdma/sf-pdma.c
> > @@ -484,21 +484,24 @@ static int sf_pdma_probe(struct platform_device *pdev)
> >         struct sf_pdma *pdma;
> >         struct sf_pdma_chan *chan;
> >         struct resource *res;
> > -       int len, chans;
> > -       int ret;
> > +       int len, ret;
> >         const enum dma_slave_buswidth widths =
> >                 DMA_SLAVE_BUSWIDTH_1_BYTE | DMA_SLAVE_BUSWIDTH_2_BYTES |
> >                 DMA_SLAVE_BUSWIDTH_4_BYTES | DMA_SLAVE_BUSWIDTH_8_BYTES |
> >                 DMA_SLAVE_BUSWIDTH_16_BYTES | DMA_SLAVE_BUSWIDTH_32_BYTES |
> >                 DMA_SLAVE_BUSWIDTH_64_BYTES;
> >
> > -       chans = PDMA_NR_CH;
> > -       len = sizeof(*pdma) + sizeof(*chan) * chans;
> > +       len = sizeof(*pdma) + sizeof(*chan) * PDMA_MAX_NR_CH;
> >         pdma = devm_kzalloc(&pdev->dev, len, GFP_KERNEL);
> >         if (!pdma)
> >                 return -ENOMEM;
> >
> > -       pdma->n_chans = chans;
> > +       ret = of_property_read_u32(pdev->dev.of_node, "dma-channels",
> > +                                  &pdma->n_chans);
> > +       if (ret) {
> > +               dev_err(&pdev->dev, "failed to read dma-channels\n");
> > +               return ret;
>
> Note that this is not backwards-compatible with existing DTBs, which
> lack the "dma-channels" property.
> Perhaps you want to fallback to a default of 4 instead?
>

Thanks for your advice. I would set n_chans to 4 in failure condition
for backwards-compatible.

> > +       }
> >
> >         res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> >         pdma->membase = devm_ioremap_resource(&pdev->dev, res);
>
> Gr{oetje,eeting}s,
>
>                         Geert
>
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
>
> 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