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:

quoted

Hi Maxime,

On Mon, Jun 30, 2014 at 02:20:54PM +0100, Maxime Ripard wrote:

quoted

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 <redacted>
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

[...]

quoted

+       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...

quoted

quoted

+       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?

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

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.

Cheers,
Mark.