linux-kernel - Re: [PATCH v2 1/2] dt-bindings: i2c: spacemit: add support for K1 SoC

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Message-ID: <a9f59ffb-23e9-4c83-8d44-4c766e32b3bf@sifive.com>
Date: Wed, 6 Nov 2024 18:29:56 -0600
From: Samuel Holland <samuel.holland@...ive.com>
To: Troy Mitchell <troymitchell988@...il.com>, andi.shyti@...nel.org,
 robh@...nel.org, krzk+dt@...nel.org, conor+dt@...nel.org
Cc: linux-i2c@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org
Subject: Re: [PATCH v2 1/2] dt-bindings: i2c: spacemit: add support for K1 SoC

Hi Troy,

On 2024-11-06 1:58 AM, Troy Mitchell wrote:
> On 2024/11/2 11:48, Samuel Holland wrote:
>> On 2024-10-28 12:32 AM, Troy Mitchell wrote:
>>> The I2C of K1 supports fast-speed-mode and high-speed-mode,
>>> and supports FIFO transmission.
>>>
>>> Signed-off-by: Troy Mitchell <TroyMitchell988@...il.com>
>>> ---
>>>  .../bindings/i2c/spacemit,k1-i2c.yaml         | 51 +++++++++++++++++++
>>>  1 file changed, 51 insertions(+)
>>>  create mode 100644 Documentation/devicetree/bindings/i2c/spacemit,k1-i2c.yaml
>>>
>>> diff --git a/Documentation/devicetree/bindings/i2c/spacemit,k1-i2c.yaml b/Documentation/devicetree/bindings/i2c/spacemit,k1-i2c.yaml
>>> new file mode 100644
>>> index 000000000000..57af66f494e7
>>> --- /dev/null
>>> +++ b/Documentation/devicetree/bindings/i2c/spacemit,k1-i2c.yaml
>>> @@ -0,0 +1,51 @@
>>> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
>>> +%YAML 1.2
>>> +---
>>> +$id: http://devicetree.org/schemas/i2c/spacemit,k1-i2c.yaml#
>>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>>> +
>>> +title: I2C controller embedded in SpacemiT's K1 SoC
>>> +
>>> +maintainers:
>>> +  - Troy Mitchell <troymitchell988@...il.com>
>>> +
>>> +properties:
>>> +  compatible:
>>> +    const: spacemit,k1-i2c
>>> +
>>> +  reg:
>>> +    maxItems: 2
>>> +
>>> +  interrupts:
>>> +    maxItems: 1
>>> +
>>> +  clocks:
>>> +    maxItems: 1
>>
>> Looking at the K1 user manual (9.1.4.77 RCPU I2C0 CLOCK RESET CONTROL
>> REGISTER(RCPU_I2C0_CLK_RST)), I see two clocks (pclk, fclk) and a reset, which
>> looks to be standard across the peripherals in this SoC. Please be sure that the
>> binding covers all resources needed to use this peripheral.
>
> RCPU stands for Real-time CPU, which is typically used for low power consumption
> applications.
> We should be using the APBC_TWSIx_CLK_RST register, but it's not listed in the
> user manual. However, you can find this register referenced in the K1 clock patch:
> https://lore.kernel.org/all/SEYPR01MB4221AA2CA9C91A695FEFA777D7602@SEYPR01MB4221.apcprd01.prod.exchangelabs.com/

Ah, well that driver is missing most of the bus clocks. For example, from a
quick comparison with the manual, the driver includes sdh_axi_aclk, but misses
all of the PWM APB clocks at APBC_PWMx_CLK_RST bit 0.

If the clock gate exists in the hardware, even if it is enabled by default, it
needs to be modeled in the devicetree.

> Also, to see how to enable the I2C clock in the device tree (note that the
> spacemit,apb_clock property is unused in the driver), check out the example here:
> https://gitee.com/bianbu-linux/linux-6.1/blob/bl-v1.0.y/arch/riscv/boot/dts/spacemit/k1-x.dtsi#L1048

The devicetree describes the hardware, irrespective of which features the driver
may or may not use.

>>> +
>>> +  clock-frequency:
>>> +    description:
>>> +      Desired I2C bus clock frequency in Hz. As only fast and high-speed
>>> +      modes are supported by hardware, possible values are 100000 and 400000.
>>> +    enum: [100000, 400000]
>>
>> This looks wrong. In the manual I see:
>>
>> * Supports standard-mode operation up to 100 Kbps
>> * Supports fast-mode operation up to 400Kbps
>> * Supports high-speed mode (HS mode) slave operation up to 3.4Mbps(High-speed
>> I2C only)
>> * Supports high-speed mode (HS mode) master operation up to 3.3 Mbps (High-speed
>> I2C only)
>>
>> So even ignoring HS mode, 100 kHz and 400 kHz are only the maximums, not fixed
>> frequencies.
> okay. I will fix it in next version.
> and should I keep to ignore high-speed mode here?
> if not, how about this:
> 
>   clock-frequency:
>     description:
>       Desired I2C bus clock frequency in Hz.
>       K1 supports standard, fast, high-speed modes, from 1 to 3300000.
>     default: 100000
>     minimum: 1
>     maximum: 3300000

I don't know if high-speed mode should be included, since it requires some extra
negotiation to use. Assuming it should be, that looks reasonable.

Regards,
Samuel

>>
>> Regards,
>> Samuel
>>
>>> +    default: 100000
>>> +
>>> +required:
>>> +  - compatible
>>> +  - reg
>>> +  - interrupts
>>> +  - clocks
>>> +
>>> +unevaluatedProperties: false
>>> +
>>> +examples:
>>> +  - |
>>> +    i2c@...10800 {
>>> +        compatible = "spacemit,k1-i2c";
>>> +        reg = <0x0 0xd4010800 0x0 0x38>;
>>> +        interrupt-parent = <&plic>;
>>> +        interrupts = <36>;
>>> +        clocks = <&ccu 90>;
>>> +        clock-frequency = <100000>;
>>> +    };
>>> +
>>> +...
>>
>