Re: [PATCH v2 3/3] dmaengine: sf-pdma: Get number of channel by device tree

[Geert Uytterhoeven <geert@linux-m68k.org>]

Hi Zong,

On Tue, Jan 11, 2022 at 9:51 AM Zong Li <zong.li@sifive.com> wrote:
> It currently assumes that there are always four channels, it would
> cause the error if there is actually less than four channels. Change
> that by getting number of channel from device tree.
>
> For backwards-compatible, it uses the default value (i.e. 4) when there
> is no 'dma-channels' information in dts.
>
> 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;

Why is the last part added (yes, this is a pre-existing issue)?
struct sf_pdma already contains space for chans[PDMA_MAX_NR_CH].
Either drop the last part, or change sf_pdma.chans[] to a flexible
array member.

BTW, you can use the struct_size() or flex_array_size() helper
to calculate len.

>         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_notice(&pdev->dev, "set number of channels to default value: 4\n");
> +               pdma->n_chans = PDMA_MAX_NR_CH;
> +       }
>
>         res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
>         pdma->membase = devm_ioremap_resource(&pdev->dev, res);
> @@ -556,7 +559,7 @@ static int sf_pdma_remove(struct platform_device *pdev)
>         struct sf_pdma_chan *ch;
>         int i;
>
> -       for (i = 0; i < PDMA_NR_CH; i++) {
> +       for (i = 0; i < pdma->n_chans; i++) {
>                 ch = &pdma->chans[i];

If dma-channels in DT > PDMA_NR_CH, this becomes an out-of-bound
access.

>
>                 devm_free_irq(&pdev->dev, ch->txirq, ch);
> diff --git a/drivers/dma/sf-pdma/sf-pdma.h b/drivers/dma/sf-pdma/sf-pdma.h
> index 0c20167b097d..8127d792f639 100644
> --- a/drivers/dma/sf-pdma/sf-pdma.h
> +++ b/drivers/dma/sf-pdma/sf-pdma.h
> @@ -22,11 +22,7 @@
>  #include "../dmaengine.h"
>  #include "../virt-dma.h"
>
> -#define PDMA_NR_CH                                     4
> -
> -#if (PDMA_NR_CH != 4)
> -#error "Please define PDMA_NR_CH to 4"
> -#endif
> +#define PDMA_MAX_NR_CH                                 4
>
>  #define PDMA_BASE_ADDR                                 0x3000000
>  #define PDMA_CHAN_OFFSET                               0x1000
> @@ -118,7 +114,7 @@ struct sf_pdma {
>         void __iomem            *membase;
>         void __iomem            *mappedbase;
>         u32                     n_chans;
> -       struct sf_pdma_chan     chans[PDMA_NR_CH];
> +       struct sf_pdma_chan     chans[PDMA_MAX_NR_CH];
>  };
>
>  #endif /* _SF_PDMA_H */
-
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