Re: [PATCH v3 07/11] dt-bindings: clock: Add StarFive JH7110 system clock and reset generator

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

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Hal, Rob, Krzysztof,

On Fri, Feb 17, 2023 at 08:20:14PM +0800, Hal Feng wrote:
> On Fri, 17 Feb 2023 07:51:24 +0000, Conor Dooley wrote:
> > On Fri, Feb 17, 2023 at 10:27:27AM +0800, Hal Feng wrote:
> >> On Thu, 16 Feb 2023 18:20:34 +0000, Conor Dooley wrote:
> >> > Hey Hal!
> >> > 
> >> > On Thu, Feb 16, 2023 at 10:42:20PM +0800, Hal Feng wrote:
> >> >> On Tue, 27 Dec 2022 20:15:20 +0000, Conor Dooley wrote:
> >> >> > On Mon, Dec 26, 2022 at 12:26:32AM +0800, Hal Feng wrote:
> >> >> >> On Tue, 20 Dec 2022 23:14:39 +0000, Conor Dooley wrote:
> >> >> >> > On Tue, Dec 20, 2022 at 08:50:50AM +0800, Hal Feng wrote:
> >> >> >> > > From: Emil Renner Berthing <kernel@esmil.dk>
> >> >> >> > > 
> >> >> >> > > Add bindings for the system clock and reset generator (SYSCRG) on the
> >> >> >> > > JH7110 RISC-V SoC by StarFive Ltd.
> >> >> >> > > 
> >> >> >> > > Signed-off-by: Emil Renner Berthing <kernel@esmil.dk>
> >> >> >> > > Signed-off-by: Hal Feng <hal.feng@starfivetech.com>
> >> >> > 
> >> >> >> > > +  clocks:
> >> >> >> > > +    items:
> >> >> >> > > +      - description: Main Oscillator (24 MHz)
> >> >> >> > > +      - description: GMAC1 RMII reference
> >> >> >> > > +      - description: GMAC1 RGMII RX
> >> >> >> > > +      - description: External I2S TX bit clock
> >> >> >> > > +      - description: External I2S TX left/right channel clock
> >> >> >> > > +      - description: External I2S RX bit clock
> >> >> >> > > +      - description: External I2S RX left/right channel clock
> >> >> >> > > +      - description: External TDM clock
> >> >> >> > > +      - description: External audio master clock
> >> >> >> > 
> >> >> >> > So, from peeking at the clock driver & the dt - it looks like a bunch of
> >> >> >> > these are not actually required?
> >> >> >> 
> >> >> >> These clocks are used as root clocks or optional parent clocks in clock tree.
> >> >> >> Some of them are optional, but they are required if we want to describe the
> >> >> >> complete clock tree of JH7110 SoC.
> >> >> > 
> >> >> > Perhaps I have a misunderstand of what required means. To me, required
> >> >> > means "you must provide this clock for the SoC to operate in all
> >> >> > configurations".
> >> >> > Optional therefore would be for things that are needed only for some
> >> >> > configurations and may be omitted if not required.
> >> >> > 
> >> >> > From your comment below, boards with a JH7110 may choose not to populate
> >> >> > both external clock inputs to a mux. In that case, "dummy" clocks should
> >> >> > not have to be provided in the DT of such boards to satisfy this binding
> >> >> > which seems wrong to me..
> >> >> 
> >> >> Please see the picture of these external clocks in clock tree.
> >> >> 
> >> >> # mount -t debugfs none /mnt
> >> >> # cat /mnt/clk/clk_summary
> >> >>                                  enable  prepare  protect                                duty  hardware
> >> >>    clock                          count    count    count        rate   accuracy phase  cycle    enable
> >> >> -------------------------------------------------------------------------------------------------------
> >> >>  *mclk_ext*                             0        0        0    12288000          0     0  50000         Y
> >> >>  *tdm_ext*                              0        0        0    49152000          0     0  50000         Y
> >> >>  *i2srx_lrck_ext*                       0        0        0      192000          0     0  50000         Y
> >> >>  *i2srx_bclk_ext*                       0        0        0    12288000          0     0  50000         Y
> >> >>  *i2stx_lrck_ext*                       0        0        0      192000          0     0  50000         Y
> >> >>  *i2stx_bclk_ext*                       0        0        0    12288000          0     0  50000         Y
> >> >>  *gmac1_rgmii_rxin*                     0        0        0   125000000          0     0  50000         Y
> >> >>     gmac1_rx                          0        0        0   125000000          0     0  50000         Y
> >> >>        gmac1_rx_inv                   0        0        0   125000000          0   180  50000         Y
> >> >>  *gmac1_rmii_refin*                     0        0        0    50000000          0     0  50000         Y
> >> >>     gmac1_rmii_rtx                    0        0        0    50000000          0     0  50000         Y
> >> >>        gmac1_tx                       0        0        0    50000000          0     0  50000         N
> >> >>           gmac1_tx_inv                0        0        0    50000000          0   180  50000         Y
> >> >>  *osc*                                  4        4        0    24000000          0     0  50000         Y
> >> >>     apb_func                          0        0        0    24000000          0     0  50000         Y
> >> >>  ...
> >> >> 
> >> >> The clock "gmac1_rgmii_rxin" and the clock "gmac1_rmii_refin" are
> >> >> actually used as the parent of other clocks.
> >> > 
> >> >> The "dummy" clocks
> >> >> you said are all internal clocks.
> >> > 
> >> > No, what I meant by "dummy" clocks is that if you make clocks "required"
> >> > in the binding that are not needed by the hardware for operation a
> >> > customer of yours might have to add "dummy" clocks to their devicetree
> >> > to pass dtbs_check.
> >> > 
> >> >> For the audio related clocks (mclk_ext/tdm_ext/i2srx_lrck_ext/
> >> >> i2srx_bclk_ext/i2stx_lrck_ext/i2stx_bclk_ext), they will be used
> >> >> as the parent clocks in audio related drivers. Note that some
> >> >> clocks need to select different clocks as parent according to
> >> >> requirement.
> >> >> So all these external clocks are required.
> >> >> 
> >> >> > 
> >> >> > It would seem to me that you need to set minItems < maxItems here to
> >> >> > account for that & you do in fact need clock-names.
> >> >> > 
> >> >> >> 
> >> >> >> > I'd have ploughed through this, but having read Krzysztof's comments on
> >> >> >> > the DTS I'm not sure that this binding is correct.
> >> >> >> > https://lore.kernel.org/linux-riscv/20221220011247.35560-1-hal.feng@starfivetech.com/T/#mdf67621a2344dce801aa8015d4963593a2c28bcc
> >> >> >> > 
> >> >> >> > I *think* the DT is correct - the fixed clocks are all inputs from clock
> >> >> >> > sources on the board and as such they are empty in soc.dtsi and are
> >> >> >> > populated in board.dts?
> >> >> >> 
> >> >> >> Yes, the fixed clocks are all clock sources on the board and input to the SoC.
> >> >> >> 
> >> >> >> > 
> >> >> >> > However, are they all actually required? In the driver I see:
> >> >> >> > 	JH71X0__MUX(JH7110_SYSCLK_GMAC1_RX, "gmac1_rx", 2,
> >> >> >> > 		    JH7110_SYSCLK_GMAC1_RGMII_RXIN,
> >> >> >> > 		    JH7110_SYSCLK_GMAC1_RMII_RTX),
> >> >> >> > That macro is:
> >> >> >> > #define JH71X0__MUX(_idx, _name, _nparents, ...) [_idx] = {			\
> >> >> >> > 	.name = _name,								\
> >> >> >> > 	.flags = 0,								\
> >> >> >> > 	.max = ((_nparents) - 1) << JH71X0_CLK_MUX_SHIFT,			\
> >> >> >> > 	.parents = { __VA_ARGS__ },						\
> >> >> >> > }
> >> > 
> >> >> >> > AFAICT, RMII reference feeds RMII_RTX & RGMII RX *is* RGMII_RXIN?
> >> >> >> > Does that mean you need to populate only one of GMAC1 RMII reference
> >> >> >> > and GMAC1 RMGII RX and the other is optional?
> >> > 
> >> >> >> Yes, actually only one of them is chosen as the root clock
> >> >> >> source of the clock "gmac1_rx".
> >> > |  *gmac1_rgmii_rxin*   
> >> > |     gmac1_rx          
> >> > |        gmac1_rx_inv   
> >> > |  *gmac1_rmii_refin*   
> >> > |     gmac1_rmii_rtx    
> >> > |        gmac1_tx       
> >> > |           gmac1_tx_inv
> >> > |
> >> > | description: GMAC1 RMII reference
> >> > | description: GMAC1 RGMII RX
> >> > 
> >> > 
> >> > So you're telling me that you can either:
> >> > - Provide GMAC1 RMII reference and GMAC1 RGMII RX & then use different
> >> >   clocks for gmac1_rx and gmac1_tx
> >> > - Provide only GMAC1 RMII reference & use it for both gmac1_tx *and*
> >> >   gmac1_rx
> >> > 
> >> > Is that correct?
> >> 
> >> Yes, it is.
> > 
> > Which would then make GMAC1 RGMII RX optional, rather than required?
> 
> If thinking in this way, I must say yes, it is optional. But actually
> GMAC1 RGMII RX feeds gmac1_rx by default. 
> For a mux, it usually works if you populate only one input to it.
> Does it mean all the other inputs are optional? And how can we define
> which input is required?

I'm not sure, that is a question for Krzysztof and/or Rob.

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