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

[Zong Li <zong.li@sifive.com>]

On Wed, Jan 12, 2022 at 4:28 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
>
> 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.

Thanks for your suggestions, let me fix it in the next version.

>
> >         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.
>

Okay, let me get the min() between pdma->chans and PDMA_MAX_NR_CH,
please let me know if it isn't good to you.

> >
> >                 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