Re: [PATCH v10 2/2] dmaengine: sun6i: Add driver for the Allwinner A31 DMA controller

Maxime Ripard
2014-06-30T15:20:06Z

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On Mon, Jun 30, 2014 at 03:20:54PM +0100, Mark Rutland wrote:
> Hi Maxime,
>
> On Mon, Jun 30, 2014 at 02:20:54PM +0100, Maxime Ripard wrote:
> > The Allwinner A31 has a 16 channels DMA controller that it shares with the
> > newer A23. Although sharing some similarities with the DMA controller of the
> > older Allwinner SoCs, it's significantly different, I don't expect it to be
> > possible to share the driver for these two.
> >
> > The A31 Controller is able to memory-to-memory or memory-to-device transfers on
> > the 16 channels in parallel.
> >
> > Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
> > Acked-by: Arnd Bergmann <arnd@arndb.de>
> > ---
> > drivers/dma/Kconfig | 8 +
> > drivers/dma/Makefile | 1 +
> > drivers/dma/sun6i-dma.c | 1058 +++++++++++++++++++++++++++++++++++++++++++++++
> > 3 files changed, 1067 insertions(+)
> > create mode 100644 drivers/dma/sun6i-dma.c
>
> [...]
>
> > + sdc->clk = devm_clk_get(&pdev->dev, NULL);
> > + if (IS_ERR(sdc->clk)) {
> > + dev_err(&pdev->dev, "No clock specified\n");
> > + return PTR_ERR(sdc->clk);
> > + }
> > +
> > + mux = clk_get(NULL, "ahb1_mux");
> > + if (IS_ERR(mux)) {
> > + dev_err(&pdev->dev, "Couldn't get AHB1 Mux\n");
> > + return PTR_ERR(mux);
> > + }
> > +
> > + pll6 = clk_get(NULL, "pll6");
> > + if (IS_ERR(pll6)) {
> > + dev_err(&pdev->dev, "Couldn't get PLL6\n");
> > + clk_put(mux);
> > + return PTR_ERR(pll6);
> > + }
>
> I'm slightly confused. The binding listed a single unnamed clock (the
> AHB clock). What is going on here?

The device itself needs only a single clock to work...

>
> > + ret = clk_set_parent(mux, pll6);
> > + clk_put(pll6);
> > + clk_put(mux);
> > +
> > + if (ret) {
> > + dev_err(&pdev->dev, "Couldn't reparent AHB1 on PLL6\n");
> > + return ret;
> > + }
>
> Why do we need to reparent the mux?

... but will function only if this clock is derived from PLL6.

Maxime

--
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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