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

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Date:   Mon, 10 Jan 2022 09:57:51 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Zong Li <zong.li@...ive.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>,
        Conor Dooley <conor.dooley@...rochip.com>,
        Bin Meng <bin.meng@...driver.com>, green.wan@...ive.com,
        Vinod <vkoul@...nel.org>, dmaengine <dmaengine@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-riscv <linux-riscv@...ts.infradead.org>
Subject: Re: [PATCH 3/3] dmaengine: sf-pdma: Get number of channel by device tree

Hi Zong,

On Wed, Jan 5, 2022 at 6:44 AM Zong Li <zong.li@...ive.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@...ive.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?

> +       }
>
>         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@...ux-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