RE: [PATCH 1/4] dt-bindings: firmware: imx-scu: new binding to parse clocks from device tree

[Aisheng Dong <aisheng.dong@nxp.com>]

> From: Rob Herring [mailto:robh@kernel.org]
> Sent: Tuesday, March 26, 2019 9:47 PM
> On Thu, Feb 21, 2019 at 06:03:43PM +0000, Aisheng Dong wrote:
> > There's a few limitations on one cell clock binding (#clock-cells =
> > <1>) that we have to define all clock IDs for device tree to reference.
> > This may cause troubles if we want to use common clock IDs for multi
> > platforms support when the clock of those platforms are mostly the same.
> > e.g. Current clock IDs name are defined with SS prefix. However the
> > device may reside in different SS across CPUs, that means the SS
> > prefix may not valid anymore for a new SoC. Furthermore, the device
> > availability of those clocks may also vary a bit.
> >
> > For such situation, We formerly planned to add all new IDs for each SS
> > and dynamically check availability for different SoC in driver. That
> > can be done but that may involve a lot effort and may result in more
> > changes and duplicated code in driver, also make device tree
> > upstreaming hard which depends on Clock IDs.
> >
> > To relief this situation, we want to move the clock definition into
> > device tree which can fully decouple the dependency of Clock ID
> > definition from device tree. And no frequent changes required in clock driver
> any more.
> >
> > Then we can use the existence of clock nodes in device tree to address
> > the device and clock availability differences across different SoCs.
> >
> > For SCU clocks, only two params required, thus two new property created:
> > rsrc-id = <IMX_SC_R_UART_0>;
> > clk-type = <IMX_SC_PM_CLK_PER>;
> >
> > And as we want to support clock set parent function, 'clocks' property
> > is also used to pass all the possible input parents.
> >
> > Cc: Rob Herring <robh@kernel.org>
> > Cc: Stephen Boyd <sboyd@kernel.org>
> > Cc: Shawn Guo <shawnguo@kernel.org>
> > Cc: Sascha Hauer <kernel@pengutronix.de>
> > Cc: Michael Turquette <mturquette@baylibre.com>
> > Cc: devicetree@vger.kernel.org
> > Signed-off-by: Dong Aisheng <aisheng.dong@nxp.com>
> > ---
> >  .../devicetree/bindings/arm/freescale/fsl,scu.txt  | 29
> ++++++++++++++++------
> >  include/dt-bindings/firmware/imx/rsrc.h            | 17
> +++++++++++++
> >  2 files changed, 38 insertions(+), 8 deletions(-)
> >
> > diff --git
> > a/Documentation/devicetree/bindings/arm/freescale/fsl,scu.txt
> > b/Documentation/devicetree/bindings/arm/freescale/fsl,scu.txt
> > index 72d481c..2816789 100644
> > --- a/Documentation/devicetree/bindings/arm/freescale/fsl,scu.txt
> > +++ b/Documentation/devicetree/bindings/arm/freescale/fsl,scu.txt
> > @@ -78,6 +78,19 @@ Required properties:
> >  			  "fsl,imx8qm-clock"
> >  			  "fsl,imx8qxp-clock"
> >  			followed by "fsl,scu-clk"
> > +- #clock-cells:		Should be 0.
> > +- rsrc-id:		Resource ID associated with this clock
> > +- clk-type:		Type of this clock.
> > +			Refer to <include/dt-bindings/firmware/imx/rsrc.h> for
> > +			available clock types supported by SCU.
> 
> Can't you just make these 2 values clock cells? I'm all for getting rid of made
> up clock numbers.
> 

Thanks for the agreement to remove clock IDs.

The 2 values clock cell seems not the best approach for i.MX because it still needs
to define all clocks in the driver which is exactly we want to avoid now due to some
special HW characteristic:
1. clock resources may be allocated to different SW execution partition by firmware
and A core may not have access rights for those clocks not belong to its partition.
So we want to describe them in DT according to the partition configuration.

2. Each clock is associated with a different power domain which is better to be
described in device tree. And clock state will be lost and need restore after power cycle
of the domain.

Based on above requirements, do you think we can do as below?

//LSIO SS
lsio_scu_clk: lsio-scu-clock-controller {
        compatible = "fsl,imx8qxp-clock", "fsl,scu-clk";

        fspi0_clk: clock-fspi0{
                #clock-cells = <0>;
                rsrc-id = <IMX_SC_R_FSPI_0>;
                clk-type = <IMX_SC_PM_CLK_PER>;
                power-domains = <&pd IMX_SC_R_FSPI_0>;
        };
		
		fspi1_clk: clock-fspi1{
			...
		};
        ...
};    

/* LPCG clocks */
lsio_lpcg_clk: lsio-lpcg-clock-controller {
        compatible = "fsl,imx8qxp-lpcg";

        pwm0_lpcg: clock-controller@5d400000 {
                reg = <0x5d400000 0x10000>;
                #clock-cells = <1>;
                clocks = <&pwm0_clk>, <&pwm0_clk>, <&pwm0_clk>,
                         <&lsio_bus_clk>, <&pwm0_clk>;
                bit-offset = <0 4 16 20 24>;
                clock-output-names = "pwm0_lpcg_ipg_clk",
                                     "pwm0_lpcg_ipg_hf_clk",
                                     "pwm0_lpcg_ipg_s_clk",
                                     "pwm0_lpcg_ipg_slv_clk",
                                     "pwm0_lpcg_ipg_mstr_clk";
                power-domains = <&pd IMX_SC_R_PWM_0>;
                status = "disabled";
        };

		pwm1_lpcg: clock-controller@5d410000 {
				...
		}
        ...
};

And for users, it could simply be:
usdhc1: mmc@5b010000 {
        clocks = <&sdhc0_lpcg 1>,
                 <&sdhc0_lpcg 0>,
                 <&sdhc0_lpcg 2>;
        clock-names = "ipg", "per", "ahb";
        assigned-clocks = <&sdhc0_clk>;
        assigned-clock-rates = <200000000>;
		....
};

Regards
Dong Aisheng

> > +- clock-output-names:	Shall be the corresponding names of the outputs.
> > +
> > +Optional properties:
> > +- clocks:		Shall be the input parent clock(s) phandle for the clock.
> > +			For multiplexed clocks, the list order must match the hardware
> > +			programming order.
> > +
> > +Legacy Clock binding (DEPRECATED):
> >  - #clock-cells:		Should be 1. Contains the Clock ID value.
> >  - clocks:		List of clock specifiers, must contain an entry for
> >  			each required entry in clock-names @@ -129,6 +142,13 @@
> lsio_mu1:
> > mailbox@5d1c0000 {
> >  	#mbox-cells = <2>;
> >  };
> >
> > +uart0_clk: uart0-clock-controller {
> > +	compatible = "fsl,imx8qxp-scu-pd", "fsl,scu-clk";
> > +	#clock-cells = <0>;
> > +	rsrc-id = <IMX_SC_R_UART_0>;
> > +	clk-type = <IMX_SC_PM_CLK_PER>;
> > +};
> > +
> >  firmware {
> >  	scu {
> >  		compatible = "fsl,imx-scu";
> > @@ -143,11 +163,6 @@ firmware {
> >  			  &lsio_mu1 1 2
> >  			  &lsio_mu1 1 3>;
> >
> > -		clk: clk {
> > -			compatible = "fsl,imx8qxp-clk", "fsl,scu-clk";
> > -			#clock-cells = <1>;
> > -		};
> > -
> >  		iomuxc {
> >  			compatible = "fsl,imx8qxp-iomuxc";
> >
> > @@ -175,8 +190,6 @@ serial@5a060000 {
> >  	...
> >  	pinctrl-names = "default";
> >  	pinctrl-0 = <&pinctrl_lpuart0>;
> > -	clocks = <&clk IMX8QXP_UART0_CLK>,
> > -		 <&clk IMX8QXP_UART0_IPG_CLK>;
> > -	clock-names = "per", "ipg";
> > +	clocks = <&uart0_clk>;
> >  	power-domains = <&pd IMX_SC_R_UART_0>;  }; diff --git
> > a/include/dt-bindings/firmware/imx/rsrc.h
> > b/include/dt-bindings/firmware/imx/rsrc.h
> > index 4481f2d..f650fc3 100644
> > --- a/include/dt-bindings/firmware/imx/rsrc.h
> > +++ b/include/dt-bindings/firmware/imx/rsrc.h
> > @@ -556,4 +556,21 @@
> >  #define IMX_SC_R_VPU			540
> >  #define IMX_SC_R_LAST			541
> >
> > +/*
> > + * Defines for SC PM CLK
> > + */
> > +#define IMX_SC_PM_CLK_SLV_BUS		0	/* Slave bus clock */
> > +#define IMX_SC_PM_CLK_MST_BUS		1	/* Master bus clock */
> > +#define IMX_SC_PM_CLK_PER		2	/* Peripheral clock */
> > +#define IMX_SC_PM_CLK_PHY		3	/* Phy clock */
> > +#define IMX_SC_PM_CLK_MISC		4	/* Misc clock */
> > +#define IMX_SC_PM_CLK_MISC0		0	/* Misc 0 clock */
> > +#define IMX_SC_PM_CLK_MISC1		1	/* Misc 1 clock */
> > +#define IMX_SC_PM_CLK_MISC2		2	/* Misc 2 clock */
> > +#define IMX_SC_PM_CLK_MISC3		3	/* Misc 3 clock */
> > +#define IMX_SC_PM_CLK_MISC4		4	/* Misc 4 clock */
> > +#define IMX_SC_PM_CLK_CPU		2	/* CPU clock */
> > +#define IMX_SC_PM_CLK_PLL		4	/* PLL */
> > +#define IMX_SC_PM_CLK_BYPASS		4	/* Bypass clock */
> > +
> >  #endif /* __DT_BINDINGS_RSCRC_IMX_H */
> > --
> > 2.7.4
> >