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

Mark Rutland
2014-06-30T14:21:46Z

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?

> + 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?

Thanks,
Mark.