Re: [PATCH v2 6/6] arm64: dts: berlin4ct: add pll and clock nodes

[Jisheng Zhang]

On Mon, 23 Nov 2015 09:30:42 +0100
Sebastian Hesselbarth wrote:

> On 23.11.2015 08:21, Jisheng Zhang wrote:
> > On Fri, 20 Nov 2015 22:06:59 +0100
> > Sebastian Hesselbarth wrote:  
> >> On 20.11.2015 09:42, Jisheng Zhang wrote:  
> >>> Add syspll, mempll, cpupll, gateclk and berlin-clk nodes.
> >>>
> >>> Signed-off-by: Jisheng Zhang <jszhang@xxxxxxxxxxx>
> >>> ---  
> [...]
> >>> +		syspll: syspll {
> >>> +			compatible = "marvell,berlin-pll";
> >>> +			reg = <0xea0200 0x14>, <0xea0710 4>;
> >>> +			#clock-cells = <0>;
> >>> +			clocks = <&osc>;
> >>> +			bypass-shift = /bits/ 8 <0>;
> >>> +		};
> >>> +
> >>> +		gateclk: gateclk {
> >>> +			compatible = "marvell,berlin4ct-gateclk";
> >>> +			reg = <0xea0700 4>;
> >>> +			#clock-cells = <1>;
> >>> +		};
> >>> +
> >>> +		clk: clk {
> >>> +			compatible = "marvell,berlin4ct-clk";
> >>> +			reg = <0xea0720 0x144>;  
> >>
> >> Looking at the reg ranges, I'd say that they are all clock related
> >> and pretty close to each other:
> >>
> >> gateclk: reg = <0xea0700 4>;
> >> bypass:  reg = <0xea0710 4>;
> >> clk:     reg = <0xea0720 0x144>;  
> >
> > Although these ranges sit close, but we should represent HW structure as you
> > said.  
> 
> Then how do you argue that you have to share the gate clock register
> with every PLL? The answer is quite simple: You are not separating by
> HW either but existing SW API.

No, PLLs don't share register any more. You can find what all clock nodes will
look like in:

http://lists.infradead.org/pipermail/linux-arm-kernel/2015-November/387322.html

> 
> If you would really want to just describe the HW, then you'd have to
> have a single node for _all_ clocks that get controlled by 0xea0700/0x4,
> feed some 32+ clocks into the node, and out again. Obviously, this
> isn't what we want, right?

I represented the HW by "kind", for example, gateclks, common-clks, pllclk.
And let common PLLs follow this rule as well:

one node for all common plls

reg <0x922000 0x14>, <0x940034 0x14>, <0xea0200 0x14>

> 
> So, the idea of berlin2 sysctrl nodes (and similar other SoCs) is: Some
> SoCs just dump some functions into a bunch of registers with no
> particular order. We'd never find a good representation for that in DT,
> so we don't bother to try but let the driver implementation deal with
> the mess. Using "simple-mfd" is a nice solution to scattered registers
> please have a look at it and come up with a cleaner separation for bg4
> clock.
> 
> > First of all, let me describe the clks/plls in BG4CT. BG4CT contains:
> >
> > two kinds of PLL: normal PLL and AVPLL. These PLLs are put with their users
> > together. For example: mempll pll registers <0xf7940034, 0x14> is put together
> > with mem controller registers. AVPLL control registers are put with AV devices.  
> 
> Why didn't you choose to have a memory-controller node that provides
> mempll clock then? I am open to having multiple nodes providing clocks
> but having a node for every clock in any subsystem is something I'll
> not even think about.

OK. As you said, "SoCs just dump some functions into a bunch of registers with
no particular order", BG4CT is now cleaner, all common-clks are put together,
gate-clks are put together, pllclks are put together, only the common PLLs
are dumped here and there. So how about representing the HW by "kind", one
node for common plls, one node for gateclks, one node for common clks and 
one node for pllclks?

                pll: pll {
                        compatible = "marvell,berlin4ct-pll";
                        reg = <0x922000 0x14>, <0x940034 0x14>, <0xea0200 0x14>
                        #clock-cells = <0>;
                        clocks = <&osc>;
                };

		pllclk: pllclk {
                        compatible = "marvell,berlin4ct-pllclk";
                        reg = <0xea0710 4>
                        #clock-cells = <1>;
		};

                gateclk: gateclk {
                        compatible = "marvell,berlin4ct-gateclk";
                        reg = <0xea0700 4>;
                        #clock-cells = <1>;
                };

                clk: clk {
                        compatible = "marvell,berlin4ct-clk";
                        reg = <0xea0720 0x144>;
                        #clock-cells = <1>;
                        clocks = <&pllclk SYSPLLCLK>;
                };

thanks

> 
> > You can also check mempll, cpupll and syspll ranges:
> >
> > cpupll: <0x922000 0x14>
> >
> > mempll: <0x940034 0x14>
> >
> > syspll: <0xea0200 0x14>
> >
> >
> > We have three normal PLLS: cpupll, mempll and syspll. All these three PLLs use
> > 25MHZ osc as clocksource. These plls can be bypassed. when syspll is bypassed
> > the 25MHZ osc is directly output to syspllclk. When mempll/cpupll is bypassed,
> > its corresponding fastrefclk is directly output to ddrphyclk/cpuclk:
> >
> >
> >         ---25MHZ osc----------|\
> >             ________            | |-- syspllclk
> >         ---| SYSPLL |---------|/
> >
> >
> >
> >         ---cpufastrefclk------|\
> >             ________            | |-- cpuclk
> >         ---| CPUPLL |---------|/
> >
> >
> >         ---memfastrefclk------|\
> >             ________            | |-- ddrphyclk
> >         ---| MEMPLL |---------|/
> >
> > NOTE: the fastrefclk is the so called normal clk below.
> >
> >
> >
> > two kinds of clk: normal clk and gate clk. The normal clk supports changing
> > divider, selecting clock source, disabling/enabling etc. The gate clk only
> > supports disabling/enabling. normal clks use syspllclk as clocksource, while
> > gate clks use perifsysclk as clocksource.
> >
> >
> > So what's the representing HW structure in fact? Here is my proposal:
> > 1. have mempll, cpupll and syspll node in dts  
> 
> No.
> 
> > 2. one gateclk node in dts for gateclks  
> 
> No.
> 
> > 3. one normalclk node in dts for normal clks  
> 
> No.
> 
> > 4. one ccf clock-mux for cpuclk, ddrphyclk and syspllclk.  
> 
> No.
> 
> > what do you think?  
> 
> I think that the current separation is not a good one. I am open for
> suggestions but I am not accepting single PLL/clock nodes.
> 
> >  From another side, let's have a look at driver/clk/mvebu. As can be seen,
> > different clks register are close each other, for example, gateclk and coreclk
> > in arch/arm/boot/dts/armada-xp.dtsi.
> >
> > And drivers/clk/sunxi, arch/arm/boot/dts/sun7i-a20.dtsi, the pll4, pll12, gt_clk
> > and ahb*, apb* etc...
> >
> > why these SoCs don't merge clocks/gates/plls to a single clock complex node?
> > I think that's because they are representing real HW structure.  
> 
> These SoC (at least mvebu) didn't merge them into a single clock
> complex node because nobody had a better idea or an impression of
> the consequences. Looking back with the idea of syscon/simple-mfd
> we probably would have chosen to separate differently.
> 
> >> So, please just follow the OF/driver structure we already
> >> have for Berlin2.  
> 
> To repeat: "please just follow the OF/driver structure we already
> have for Berlin2"
> 
> Sebastian
> 
> >>> +			#clock-cells = <1>;
> >>> +			clocks = <&syspll>;
> >>> +		};
> >>> +
> >>>   		soc_pinctrl: pin-controller@ea8000 {
> >>>   			compatible = "marvell,berlin4ct-soc-pinctrl";
> >>>   			reg = <0xea8000 0x14>;
> >>>  
> >>  
> >  
> 

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