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SubjectRe: [PATCH v10 2/2] dmaengine: sun6i: Add driver for the Allwinner A31 DMA controller
On Mon, Jun 30, 2014 at 04:33:05PM +0100, Mark Rutland wrote:
> On Mon, Jun 30, 2014 at 04:19:06PM +0100, Maxime Ripard wrote:
> > 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.
>
> Ok, but _why_ is that the case? Could we at least have a comment for
> that?

I have no idea, sorry.

> Where does the driver get the named clocks from if they aren't provided
> on the device node? Is there a clock-ranges somewhere?

No, it just looks up the global clock name.

> It feels a little fragile to rely on the organisation of the clock tree
> and the naming thereof. If the IP block is ever reused on an SoC with a
> different clock tree layout then we have to handle things differently.

What do you suggest then?

Maxime

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