Re: [PATCH v2 3/3] dmaengine: loongson: Add Loongson-2K0300 APB DMA mux driver

[Frank Li <Frank.li@oss.nxp.com>]

On Wed, Oct 21, 2026 at 05:34:29PM +0800, Binbin Zhou wrote:
> Hi Frank:
>
> On Fri, Oct 16, 2026 at 1:03 AM Frank Li <Frank.li@oss.nxp.com> wrote:
> >
> > On Fri, Oct 09, 2026 at 05:19:34PM +0800, Binbin Zhou wrote:
> > > The Loongson-2K0300 DMA mux is not a standalone DMA controller. It is
> > > implemented as a set of routing fields in the chip global configuration
> > > registers CHIP_CTRL13/14/15, which select which physical channel of the
> > > on-chip CMC DMA controller handles each peripheral DMA request.
> > >
> > > Add a driver that exposes these routing fields as an OF DMA router. The
> > > router's allocation callback validates the <request> <channel> <flags>
> > > specifier, programs the corresponding CHIP_CTRL register field, and then
> > > rewrites the specifier to <channel> <flags> so that the parent CMC DMA
> > > controller's xlate is used.
> > >
> > > Signed-off-by: Binbin Zhou <zhoubinbin@loongson.cn>
> > > ---
> > >  MAINTAINERS                                 |   1 +
> > >  drivers/dma/loongson/Makefile               |   1 +
> > >  drivers/dma/loongson/loongson2-apb-dmamux.c | 398 ++++++++++++++++++++
> > >  3 files changed, 400 insertions(+)
> > >  create mode 100644 drivers/dma/loongson/loongson2-apb-dmamux.c
> > >
> > > diff --git a/MAINTAINERS b/MAINTAINERS
> > > index 78622b255f88..0b0c6ea41c64 100644
> > > --- a/MAINTAINERS
> > > +++ b/MAINTAINERS
> > > @@ -15355,6 +15355,7 @@ F:    Documentation/devicetree/bindings/dma/loongson,ls2k0300-dmamux.yaml
> > >  F:   Documentation/devicetree/bindings/dma/loongson,ls2x-apbdma.yaml
> > >  F:   drivers/dma/loongson/loongson2-apb-cmc-dma.c
> > >  F:   drivers/dma/loongson/loongson2-apb-dma.c
> > > +F:   drivers/dma/loongson/loongson2-apb-dmamux.c
> > >  F:   include/dt-bindings/dma/loongson,ls2k-dmamux.h
> > >
> > >  LOONGSON LS2X I2C DRIVER
> > > diff --git a/drivers/dma/loongson/Makefile b/drivers/dma/loongson/Makefile
> > > index 48c19781e729..271fd38fa8f2 100644
> > > --- a/drivers/dma/loongson/Makefile
> > > +++ b/drivers/dma/loongson/Makefile
> > > @@ -2,3 +2,4 @@
> > >  obj-$(CONFIG_LOONGSON1_APB_DMA) += loongson1-apb-dma.o
> > >  obj-$(CONFIG_LOONGSON2_APB_DMA) += loongson2-apb-dma.o
> > >  obj-$(CONFIG_LOONGSON2_APB_CMC_DMA) += loongson2-apb-cmc-dma.o
> > > +obj-$(CONFIG_LOONGSON2_APB_CMC_DMA) += loongson2-apb-dmamux.o
> > > diff --git a/drivers/dma/loongson/loongson2-apb-dmamux.c b/drivers/dma/loongson/loongson2-apb-dmamux.c
> > > new file mode 100644
> > > index 000000000000..01bd3ce4ca25
> > > --- /dev/null
> > > +++ b/drivers/dma/loongson/loongson2-apb-dmamux.c
> > > @@ -0,0 +1,398 @@
> > ...
> > > +static int loongson2_dmamux_set_route(struct loongson2_dmamux *mux, u32 request, u32 channel)
> > > +{
> > > +     const struct loongson2_dmamux_map *map;
> > > +     u32 reg_val, route_val, high_val = 0;
> > > +
> > > +     if (request >= mux->config->num_maps)
> > > +             return -EINVAL;
> > > +
> > > +     if (channel > mux->config->max_channel)
> > > +             return -EINVAL;
> > > +
> > > +     map = &mux->config->maps[request];
> > > +
> > > +     switch (map->type) {
> > > +     case LOONGSON_DMAMUX_PAIR:
> > > +             route_val = channel / 2;
> > > +             break;
> > > +     case LOONGSON_DMAMUX_SINGLE:
> > > +             route_val = channel;
> > > +             if (map->high_reg)
> > > +                     high_val = (channel >> 2) & 0x1;
> > > +             break;
> > > +     default:
> > > +             return -EINVAL;
> > > +     }
> > > +
> > > +     guard(spinlock_irqsave)(&mux->lock);
> > > +
> > > +     /* Write the primary register field */
> > > +     reg_val = loongson2_dmamux_read(mux, map->reg);
> > > +     reg_val &= ~map->mask;
> > > +     reg_val |= field_prep(map->mask, route_val);
> > > +     loongson2_dmamux_write(mux, map->reg, reg_val);
> > > +
> > > +     /* Write the extension register field if present */
> > > +     if (map->high_reg) {
> > > +             reg_val = loongson2_dmamux_read(mux, map->high_reg);
> > > +             reg_val &= ~BIT(map->high_shift);
> > > +             reg_val |= high_val << map->high_shift;
> >
> > assign_bit(map->high_shift, &reg_val, high_val);
>
> I think `assign_bit()` here is not quite suitable, reg_val is a u32
> (returned by loongson2_dmamux_read()), but assign_bit() expects a
> `volatile unsigned long *`.
>
> How about adding a helper function:
>
> static void loongson2_dmamux_assign_bits(struct loongson2_dmamux *priv,
>                                          unsigned int reg, u32 mask, u32 val)
> {
>         u32 reg_val;
>
>         reg_val = loongson2_dmamux_read(priv, reg);
>         reg_val &= ~mask;
>         reg_val |= val & mask;
>         loongson2_dmamux_write(priv, reg, reg_val);
> }
>

Okay, if only use once, old code should be fine.

Reviewed-by: Frank Li <Frank.Li@nxp.com>