How to implement common clk in multi function controller?

How to implement common clk in multi function controller?

[Masahiro Yamada]

Hi.

I am implementing clk and reset drivers for my SoCs.
(drivers/clk/uniphier/* and drivers/reset/uniphier/*)


In my SoCs, one hardware block contains various
registers for both clock and reset controlling.
(so, it is like a MFD system controller device).
I think it is a common case.


I am guessing my device tree would be like follows:
(one syscon device contains clk and rst devices under it)

syscon {
     compatible = "socionext,uniphier-syscon",
                 "syscon", "simple-mfd";
     reg = <...   ...>;

     clk_ctrl {
            .compatible = "socionext,uniphier-clkctrl";
            #clock-cells = <1>;
     };

     rst_ctrl {
             .compatible = "socionext,uniphier-rstctrl";
             #reset-cells = <1>;
     };
};



One problem I noticed was,
we are supposed to use regmap for register access
if we use syscon.

OTOH, common clk APIs such as clk-gate, clk-divider
expect simple register access via writel()/readl().

Is it a good idea to expand such APIs to regmap?


Of course, I could my own uniphier/clk-gate.c
to use regmap as other SoCs do.

But, I think regmap is general demand, so
I am wondering if it could be supported in common parts.

Or, any other good solution exists?



-- 
Best Regards
Masahiro Yamada

Re: How to implement common clk in multi function controller?

[Vladimir Zapolskiy]

Hi Masahiro,

On 11.11.2015 05:16, Masahiro Yamada wrote:
> Hi.
> 
> I am implementing clk and reset drivers for my SoCs.
> (drivers/clk/uniphier/* and drivers/reset/uniphier/*)
> 
> 
> In my SoCs, one hardware block contains various
> registers for both clock and reset controlling.
> (so, it is like a MFD system controller device).
> I think it is a common case.
> 

I met the same problem with LPC32xx clocks, one hardware block
contains clock controller, power controller, wakeup
controllers and partially pinmux and dma configuration.

I've sent a mmio version for review some time ago, but I had
to change interface to regmap recently.

> I am guessing my device tree would be like follows:
> (one syscon device contains clk and rst devices under it)
> 
> syscon {
>      compatible = "socionext,uniphier-syscon",
>                  "syscon", "simple-mfd";
>      reg = <...   ...>;
> 
>      clk_ctrl {
>             .compatible = "socionext,uniphier-clkctrl";
>             #clock-cells = <1>;
>      };
> 
>      rst_ctrl {
>              .compatible = "socionext,uniphier-rstctrl";
>              #reset-cells = <1>;
>      };
> };
> 

Eventually I implement the same layout, but replace "syscon" and
"simple-mfd" with "simple-bus" only.

For a single interface syscon_node_to_regmap() I don't see a point to
add a dependency on MFD and syscon.

> 
> One problem I noticed was,
> we are supposed to use regmap for register access
> if we use syscon.
>
> OTOH, common clk APIs such as clk-gate, clk-divider
> expect simple register access via writel()/readl().
> 
> Is it a good idea to expand such APIs to regmap?

It might be a good idea.

> 
> Of course, I could my own uniphier/clk-gate.c
> to use regmap as other SoCs do.
> 
> But, I think regmap is general demand, so
> I am wondering if it could be supported in common parts.
> 
> Or, any other good solution exists?
>

I had to copy low-level parts from clk-gate, clk-divider and clk-mux to
my driver and reimplement them on regmap API, of course I won't call
this as a good solution, but if regmap is unavoidable, that's what remains.

--
With best wishes,
Vladimir

Re: How to implement common clk in multi function controller?

[Chen-Yu Tsai]

Hi,

On Wed, Nov 11, 2015 at 11:16 AM, Masahiro Yamada
<yamada.masahiro@socionext.com> wrote:
> Hi.
>
> I am implementing clk and reset drivers for my SoCs.
> (drivers/clk/uniphier/* and drivers/reset/uniphier/*)
>
>
> In my SoCs, one hardware block contains various
> registers for both clock and reset controlling.
> (so, it is like a MFD system controller device).
> I think it is a common case.

sunxi uses a "instance per register" design, that is each
register corresponds to one (or more, in rare cases) clock
or reset control. Each will get a separate device node in
the DT.

For registers that have both clocks and resets, they are
combined in a single driver if it makes sense (for example
serving the same set of peripherals).

See drivers/clk/sunxi/clk-usb.c for such a driver.


Regards
ChenYu

> I am guessing my device tree would be like follows:
> (one syscon device contains clk and rst devices under it)
>
> syscon {
>      compatible = "socionext,uniphier-syscon",
>                  "syscon", "simple-mfd";
>      reg = <...   ...>;
>
>      clk_ctrl {
>             .compatible = "socionext,uniphier-clkctrl";
>             #clock-cells = <1>;
>      };
>
>      rst_ctrl {
>              .compatible = "socionext,uniphier-rstctrl";
>              #reset-cells = <1>;
>      };
> };
>
>
>
> One problem I noticed was,
> we are supposed to use regmap for register access
> if we use syscon.
>
> OTOH, common clk APIs such as clk-gate, clk-divider
> expect simple register access via writel()/readl().
>
> Is it a good idea to expand such APIs to regmap?
>
>
> Of course, I could my own uniphier/clk-gate.c
> to use regmap as other SoCs do.
>
> But, I think regmap is general demand, so
> I am wondering if it could be supported in common parts.
>
> Or, any other good solution exists?
>
>
>
> --
> Best Regards
> Masahiro Yamada
> --
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