Re: [PATCH v4 1/7] dt-bindings: clock: Add StarFive JH7110 PLL clock generator

[Conor Dooley <conor.dooley@microchip.com>]

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On Fri, May 26, 2023 at 09:34:32AM +0200, Torsten Duwe wrote:
> On Wed, 24 May 2023 11:19:48 +0100
> Conor Dooley <conor.dooley@microchip.com> wrote:
> 
> > On Wed, May 24, 2023 at 05:00:02PM +0800, Xingyu Wu wrote:
> > > On 2023/5/23 19:28, Conor Dooley wrote:
> > > > On Tue, May 23, 2023 at 01:10:06PM +0200, Torsten Duwe wrote:
> > > >> On Tue, 23 May 2023 09:28:39 +0100
> > > >> Conor Dooley <conor.dooley@microchip.com> wrote:
> > > >> 
> > > >> > On Tue, May 23, 2023 at 10:56:43AM +0800, Xingyu Wu wrote:
> > > >> > > On 2023/5/19 22:16, Conor Dooley wrote:
> > > >> > > > On Fri, May 19, 2023 at 03:57:33PM +0200, Torsten Duwe
> > > >> > > > wrote:
> > > >> > > >> On Fri, May 12, 2023 at 10:20:30AM +0800, Xingyu Wu wrote:
> [...]
> 
> > > >> > > Because PLL driver is separated from SYSCRG drivers in
> > > >> > > Linux, the numbering starts from 0. But in Uboot, the PLL
> > > >> > > driver is included in the SYSCRG driver, and the number
> > > >> > > follows the SYSCRG.
> > > >> > 
> > > >> > Unfortunately, how you choose to construct your drivers has
> > > >> > nothing to do with this.
> 
> Exactly. As I wrote (quote below), the PLLx frequencies are controlled
> by the I/O block SYS_SYSCON (starting there at offset 0x18), according
> to the public datasheets. All(?) other clocks are derived from those in
> the *_CRG units. That *is* the hardware to be described, in *the* (one
> and only!) DT. U-Boot, and any OS, are free to reorganise their driver
> framework around that, but the hardware description is quite clear.

The dt-binding that is in this series specifies that the pll clock
controller is a child of the syscon:
https://lore.kernel.org/linux-riscv/20230512022036.97987-1-xingyu.wu@starfivetech.com/T/#Z2e.:..:20230512022036.97987-6-xingyu.wu::40starfivetech.com:1soc:starfive:starfive::2cjh7110-syscon.yaml

That seems correct to me & U-Boot's devicetree is not compliant.

> > > >> > These defines/numbers appear in the dts and are part of the DT
> > > >> > ABI. The same dts is supposed to work for Linux & U-Boot.
> > > >> 
> > > >> The JH7110 has 6 blocks of 64k iomem in that functional area:
> > > >> {SYS,STG,AON} x {CRG,SYSCON}. None of these has 190 clocks.
> > > >> The good news: the current DTS, as proposed here and in U-Boot
> > > >> master, provides nodes for all 6 entities. The bad news is that
> > > >> the clock assignments to those nodes and their numbering is
> > > >> messed up.
> > > >> 
> > > >> AFAICT PLL{0,1,2} _are_ generated in SYS_SYSCON and thus U-Boot
> > > >> gets it wrong, in addition to the erroneous DTS.
> > > > 
> > > > The numbers are kinda hocus-pocus anyway, they are just made up
> > > > since the clock numbering usually isn't something with a nice TRM
> > > > to go and reference (unlike interrupts which usually are
> > > > documented in that way). It is very helpful to make them aligned
> > > > some register/bit positions or, but that is not required.
> > > > IOW U-Boot is not wrong per se to use 190 instead of 0, but it is
> > > > wrong to have different numbers in both places.
> 
> U-Boot reuses the Common Clock Framework from Linux, and I'm not sure
> whether the clock IDs need to be unique in order for the appropriate
> clock to be found.

Unique within the clock controller, otherwise it is impossible to tell
the difference between <&cctrl 1> and <&cctrl 1> apart! (The same
follows even with increased #clock-cells, something must be unique).
That's besides the point of this particular issue though.

> But that would be the only restriction, if it
> applies. Even then, each driver could register a clock with its own,
> arbitrarily chosen base offset with the CCF, so each CRG unit could
> still have its own clocks enumerated starting with 0 in the DTB.
> 
> > > > It sounds like you're saying that (and I have not looked) the
> > > > U-Boot dts actually has structural difference w.r.t. what
> > > > provides which clock? If so, that'll need to be fixed
> > > > independently of the numbering problem.
> 
> > > 
> > > Oh, unfortunately, the 7110 can not support to mix the uboot dtb
> > > and linux dtb up.
> > 
> > What does "cannot support" mean? It's normal and desirable for the
> 
> IMHO "desirable" is too weak.

Yeah, agreed. I just don't like being prescriptive about what happens in
projects that I do not maintain things for I guess.

> > same dtb to be usable for both. The Linux kernel's dt-bindings are
> > used for multiple projects, not just Linux - it'd be silly for
> > U-Boot, FreeBSD etc etc to go off and each have their open set of
> > (incompatible) bindings.
> > 
> > > If boot the Linux and should use the linux dtb instead of the uboot
> > > dtb. Because all clock ids and reset ids in Linux and Uboot are
> > > different include PLL, and some modules can work in Linux but not
> > > in uboot.
> [...]
> > 
> > > I suggest to boot Linux with its own linux dtb.
> 
> This is a fragile band-aid, to be used only as a last resort. It
> creates more problems than it solves. Your DTB will then match your
> kernel, but whether it describes the actual hardware is a game of
> chance. Doesn't the VisionFive2 have an RPi connector... ?
> 
> One of the IMO few valid use cases of adding a DTB to the kernel
> at boot is OpenWRT, when you build an OS Image for a particular piece
> of hardware you have at hand.
> 
> > I suggest to make sure that you can use the same dtb for both.
> 
> Interestingly enough, U-Boot already has the PLL driver in a separate
> file. I have a half-baked patch here that moves the sys_syscon DT
> matching into that file...

If you have patches that fix the devicetree & drivers in U-Boot, please
post them. I don't really care at all which set of arbitrary numbers are
chosen (as long as there is one and one only) but it looks like U-Boot's
devicetree has an incorrect description of the clock controllers.

Thanks,
Conor.

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