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From:   Zong Li <zong.li@sifive.com>
Date:   Mon, 10 Jan 2022 18:03:20 +0800
Message-ID: <CANXhq0r_x=xW37SGJfQRs11-+VL1oJKRHe1fxk3QbT_Qzy6-dQ@mail.gmail.com>
Subject: Re: [PATCH 3/3] dmaengine: sf-pdma: Get number of channel by device tree
To:     Geert Uytterhoeven <geert@linux-m68k.org>
Cc:     Rob Herring <robh+dt@kernel.org>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>,
        Conor Dooley <conor.dooley@microchip.com>,
        Bin Meng <bin.meng@windriver.com>,
        Green Wan <green.wan@sifive.com>, Vinod <vkoul@kernel.org>,
        dmaengine <dmaengine@vger.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-riscv <linux-riscv@lists.infradead.org>
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On Mon, Jan 10, 2022 at 4:58 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
>
> Hi Zong,
>
> On Wed, Jan 5, 2022 at 6:44 AM Zong Li <zong.li@sifive.com> 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@sifive.com>
>
> 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@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