[PATCH 0/4] Add I2C support on TH1520

[Thomas Bonnefille]

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 at 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?

Best regards,
Thomas