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

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Date:   Tue, 21 Feb 2023 23:39:32 +0000
From:   Conor Dooley <conor@...nel.org>
To:     Stephen Boyd <sboyd@...nel.org>
Cc:     Hal Feng <hal.feng@...rfivetech.com>,
        linux-riscv@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-clk@...r.kernel.org, Palmer Dabbelt <palmer@...belt.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Michael Turquette <mturquette@...libre.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Emil Renner Berthing <emil.renner.berthing@...onical.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 07/11] dt-bindings: clock: Add StarFive JH7110 system
 clock and reset generator

On Tue, Feb 21, 2023 at 02:17:17PM -0800, Stephen Boyd wrote:
> Quoting Conor Dooley (2023-02-16 10:20:34)
> > 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:
> > > 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.
> 
> They can set the phandle specifier to '<0>' to fill in the required
> property when there isn't anything there. If this is inside an SoC, it
> is always connected because silicon can't change after it is made
> (unless this is an FPGA). Therefore, any and all input clocks should be
> listed as required.

> If the clk controller has inputs that are
> pads/balls/pins on the SoC then they can be optional if a valid design
> can leave those pins not connected.

From the discussion on the dts patches, where the clocks have been put
(intentionally) into board.dts, I've been under the impression that we
are in this situation.
Up to Hal to tell us if the hardware is capable of having those inputs
left unfilled!

FWIW, there's a v4 [1] of this series - but the question has yet to be
resolved.

Thanks,
Conor.

1 - https://lore.kernel.org/all/20230221024645.127922-1-hal.feng@starfivetech.com/

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