Re: [PATCH 2/2 v4] clk: Add Gemini SoC clock controller

[Geert Uytterhoeven <geert@linux-m68k.org>]

Hi Liinus,

On Thu, Jun 15, 2017 at 9:16 AM, Linus Walleij <linus.walleij@linaro.org> wrote:
> On Mon, Jun 12, 2017 at 11:02 PM, Stephen Boyd <sboyd@codeaurora.org> wrote:
>> So can the certain clks that are required to get the timer
>> going be put into CLK_OF_DECLARE_DRIVER() and then have a regular
>> platform driver for the rest of the clks that aren't required for
>> early boot? We've been doing this sort of hybrid design lately,
>> so hopefully that works here too.
>
> So I tried this hybrid approach.
>
> It works and it doesn't work, it is very annoying actually... we get
> a conflict of interest between the clock driver, the reset driver and
> the device tree bindings and how Linux uses device tree.
>
> The reason is that no less than three devices probe from the same
> device tree node, essentially this is the problem:
>
> syscon: syscon@40000000 {
>       compatible = "cortina,gemini-syscon", "syscon";
>       reg = <0x40000000 0x1000>;
>       #clock-cells = <1>;
>       #reset-cells = <1>;
> };
>
> This has already a driver in drivers/reset/reset-gemini.c
> binding and probing from "cortina,gemini-syscon".
>
> That works fine, because CLK_OF_DECLARE_DRIVER() does not
> bind to the device using the device core, and syscon will always probe
> itself when the first user tries to access it.
>
> If we make the clocks bind to the platform device, the reset
> controller will not probe, regressing the boot in another way, because
> some drivers need their reset lines.

If clocks and resets are provided by the same hardware module, you can
have a single (platform) driver registering both the clock and reset
controllers.
Cfr. drivers/clk/renesas/renesas-cpg-mssr.c.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds