Re: [PATCH v1 1/5] riscv: dts: starfive: jh7110-common: replace syscrg clock assignments

[Conor Dooley <conor@kernel.org>]

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On Wed, Jan 15, 2025 at 06:33:08AM +0000, Hal Feng wrote:
> > On 07.01.25 04:08, Conor Dooley wrote: 
> > On Sat, Jan 04, 2025 at 01:04:30PM -0800, E Shattow wrote:
> > > Hi, Conor  (added CC: Minda Chen, Hal Feng)
> > >
> > > On 1/4/25 10:33, Conor Dooley wrote:
> > > > On Thu, Jan 02, 2025 at 11:45:07AM -0800, E Shattow wrote:
> > > > > Replace syscrg assignments of clocks, clock parents, and rates,
> > > > > for compatibility with downstream boot loader SPL secondary
> > > > > program loader.
> > > > >
> > > > > Signed-off-by: E Shattow <e@freeshell.de>
> > > > > ---
> > > > >   arch/riscv/boot/dts/starfive/jh7110-common.dtsi | 12 +++++++++---
> > > > >   1 file changed, 9 insertions(+), 3 deletions(-)
> > > > >
> > > > > diff --git a/arch/riscv/boot/dts/starfive/jh7110-common.dtsi
> > > > > b/arch/riscv/boot/dts/starfive/jh7110-common.dtsi
> > > > > index 48fb5091b817..55c6743100a7 100644
> > > > > --- a/arch/riscv/boot/dts/starfive/jh7110-common.dtsi
> > > > > +++ b/arch/riscv/boot/dts/starfive/jh7110-common.dtsi
> > > > > @@ -359,9 +359,15 @@ spi_dev0: spi@0 {
> > > > >   };
> > > > >   &syscrg {
> > > > > -	assigned-clocks = <&syscrg JH7110_SYSCLK_CPU_CORE>,
> > > > > -			  <&pllclk JH7110_PLLCLK_PLL0_OUT>;
> > > > > -	assigned-clock-rates = <500000000>, <1500000000>;
> > > > > +	assigned-clocks = <&syscrg JH7110_SYSCLK_CPU_ROOT>,
> > > > > +			  <&syscrg JH7110_SYSCLK_BUS_ROOT>,
> > > > > +			  <&syscrg JH7110_SYSCLK_PERH_ROOT>,
> > > > > +			  <&syscrg JH7110_SYSCLK_QSPI_REF>;
> > > > > +	assigned-clock-parents = <&pllclk JH7110_PLLCLK_PLL0_OUT>,
> > > > > +				 <&pllclk JH7110_PLLCLK_PLL2_OUT>,
> > > > > +				 <&pllclk JH7110_PLLCLK_PLL2_OUT>,
> > > > > +				 <&syscrg JH7110_SYSCLK_QSPI_REF_SRC>;
> > > > > +	assigned-clock-rates = <0>, <0>, <0>, <0>;
> > > >
> > > > Why is assigned rates here 0s, rather than the property just removed?
> > > >
> > > > >   };
> > > > >   &sysgpio {
> > > > > --
> > > > > 2.45.2
> > > > >
> > >
> > > Assigned rates all zeroes is how it is in U-Boot. Removing the
> > > assigned-clock-rates property as suggested does work in U-Boot and
> > > Linux both.
> > >
> > > For context, U-Boot fails when replacing assigned-clocks to
> > > JH7110_SYSCLK_CPU_CORE (500MHz) and JH7110_PLLCLK_PLL0_OUT
> > (1500MHz)
> > > from Linux. So I tried to merge all properties together and in testing
> > > then U-Boot failed (or I did it wrong). However replacing the Linux
> > > properties with the U-Boot configuration (above) on Linux does work for
> > both.
> > >
> > > I do not know if this is correct but I can test any suggestions and
> > > report if they are working.
> > >
> > > Do these changes make sense? Are there other variations I should test?
> > 
> > I'd like the commit message to at least explain why these clocks need to be
> > set to zero (I assume that means disabled?). Maybe the StarFive folks know
> > why it is required?
> 
> Here "assigned-clock-rates = <0>, ..." means skipping setting clock rates.
> You can refer to
> https://github.com/devicetree-org/dt-schema/blob/main/dtschema/schemas/clock/clock.yaml/

If you check the wording there, it says:
  To skip setting parent or rate of a clock its corresponding entry should be
  set to 0, or can be omitted if it is not followed by any non-zero entry.
Since all clocks are being set to 0 above, we should be in the "can be
omitted" case for the entire property, no? That would...

> Linux here setting JH7110_SYSCLK_CPU_CORE to 500MHz and JH7110_PLLCLK_PLL0_OUT
> to 1500MHz are for increasing the CPU frequency to 1500MHz.
> 
> VF2 u-boot is still running at 1000MHz now. You failed to set JH7110_PLLCLK_PLL0_OUT
> to 1500MHz, because CPU power supply voltage needs to be increased before running at
> 1500MHz.
> 
> I think a better choice now is changing Linux device tree as follows:
> 
> &syscrg {
> 	assigned-clocks = <&syscrg JH7110_SYSCLK_CPU_ROOT>,
> 			  <&syscrg JH7110_SYSCLK_BUS_ROOT>,
> 			  <&syscrg JH7110_SYSCLK_PERH_ROOT>,
> 			  <&syscrg JH7110_SYSCLK_QSPI_REF>,
> 			  <&syscrg JH7110_SYSCLK_CPU_CORE>,
> 			  <&pllclk JH7110_PLLCLK_PLL0_OUT>;
> 	assigned-clock-parents = <&pllclk JH7110_PLLCLK_PLL0_OUT>,
> 				 <&pllclk JH7110_PLLCLK_PLL2_OUT>,
> 				 <&pllclk JH7110_PLLCLK_PLL2_OUT>,
> 				 <&syscrg JH7110_SYSCLK_QSPI_REF_SRC>;
> 	assigned-clock-rates = <0>, <0>, <0>, <0>, <500000000>, <1500000000>;
> };

...make this one a reasonable change...

> For u-boot, if there is no requirement to run u-boot at 1500MHz, just keep
> &syscrg {
> 	assigned-clock-rates = <0>, <0>, <0>, <0>;
> };

...but not this one.

> in u-boot device tree. If we need running 1500MHz in u-boot, I will send a patch
> to implement it and then &syscrg{...} in u-boot device tree can be dropped.
> 
> Best regards,
> Hal

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