Re: [PATCH 0/4] Add I2C support on TH1520

[Conor Dooley <conor@kernel.org>]

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On Fri, Apr 26, 2024 at 04:12:00PM +0200, Thomas Bonnefille wrote:
> 
> 
> On 4/25/24 6:35 PM, Conor Dooley wrote:
> > On Thu, Apr 25, 2024 at 09:51:26AM -0500, Rob Herring wrote:
> > > 
> > > On Thu, 25 Apr 2024 10:21:31 +0200, Thomas Bonnefille wrote:
> > > > This adds I2C support in the device tree of the T-Head TH1520 RISCV-SoC
> > > > and a default configuration for the BeagleV-Ahead. It appears that the
> > > > TH1520 I2C is already supported in the upstream kernel through the
> > > > Synopsis Designware I2C adapter driver.
> > > > As there is no clock driver for this board as of today, this patch
> > > > series uses a fixed-clock named i2c_ic_clk.
> > > > There is also no pinctrl driver yet so pinmux must be handled manually
> > > > for now.
> > > > It also fixes the order of the nodes in the device tree to comply with
> > > > device-tree coding-style.
> > > > 
> > > > Thomas Bonnefille (4):
> > > >    dt-bindings: i2c: dw: Document compatible thead,th1520-i2c
> > > >    riscv: boot: dts: thead: Fix node ordering in TH1520 device tree
> > > >    riscv: dts: thead: Add TH1520 I2C nodes
> > > >    riscv: dts: thead: Enable I2C on the BeagleV-Ahead
> > > > 
> > > >   .../bindings/i2c/snps,designware-i2c.yaml     |  12 ++
> > > >   .../boot/dts/thead/th1520-beaglev-ahead.dts   |  22 ++++
> > > >   arch/riscv/boot/dts/thead/th1520.dtsi         | 120 ++++++++++++++----
> > > >   3 files changed, 127 insertions(+), 27 deletions(-)
> > > > 
> > > > --
> > > > 2.44.0
> > > > 
> > > > 
> > > > 
> > > 
> > > 
> > > My bot found new DTB warnings on the .dts files added or changed in this
> > > series.
> > > 
> > > Some warnings may be from an existing SoC .dtsi. Or perhaps the warnings
> > > are fixed by another series. Ultimately, it is up to the platform
> > > maintainer whether these warnings are acceptable or not. No need to reply
> > > unless the platform maintainer has comments.
> > > 
> > > If you already ran DT checks and didn't see these error(s), then
> > > make sure dt-schema is up to date:
> > > 
> > >    pip3 install dtschema --upgrade
> > > 
> > > 
> > > New warnings running 'make CHECK_DTBS=y thead/th1520-beaglev-ahead.dtb' for 20240425082138.374445-1-thomas.bonnefille@bootlin.com:
> > > 
> > > arch/riscv/boot/dts/thead/th1520-beaglev-ahead.dtb: i2c-clock: clock-frequency:0:0: 50000000 is greater than the maximum of 5000000
> > 
> > The bot is not freaking out here, 50 MHz is indeed more than 5 MHz :)
> 
> 5MHz is the maximum clock-frequency, ie. the I2C bus frequency.
> This is actually set to 100kHz for I2C0 in the DT:
> 
> &i2c0 {
>     status = "okay";
>     clock-frequency = <100000>; <----
> ...
> };
> 
> 50MHz is the "fixed-clock" frequency, that is the clock feeding the I2C
> IP block:
> 
> i2c_ic_clk: i2c-clock {
>     compatible = "fixed-clock";
>     clock-frequency = <50000000>; <-----
>     #clock-cells = <0>;
> };
> 
> My guess is that the bot confused the clock-frequency parameter for the bus
> clock (SCL) with the i2c-ic-clock value for the controller itself during the
> checks.
> 
> Do you agree with this or am I misunderstanding the error ?
> 
> If I lower the fixed-clock frequency to eg. 100kHz, the error is gone. But I
> guess the 5MHz limit should probably not apply to the input clock?

Heh, I know why that's happening - it's your node name.
The pattern for i2c controllers is "^i2c(@.*)?":
https://github.com/devicetree-org/dt-schema/blob/main/dtschema/schemas/i2c/i2c-controller.yaml

Rob co-incidentally (or maybe not) put out a patch for fixed-frequency
clock names, suggesting using clock as a prefix:
https://lore.kernel.org/all/20240425183810.3079069-1-robh@kernel.org/
If we switched to that format, I believe your problem goes away.

Cheers,
Conor.

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