Common: add patch to support dynamic I2C bus speed configuration

[S-J-Tang]

Summary

Description

• Add Nuvoton patch 0035 for the NPCM4xx I2C driver (Zephyr tag v2.6.0.0).
• Support independent SCL low/high timing for fast mode (400 kHz) and fast-plus mode (1 MHz).
• Add an i2c speed shell command to change the bus speed at runtime.

Motivation

• The driver only has one scllt/sclht pair, and it is applied to both 400 kHz and 1 MHz.

Design

• Add two optional DTS properties, scllt_fp and sclht_fp, for fast-plus mode.
• i2c_npcm4xx_set_baudrate() selects the timing pair by the requested speed:
  • bus_freq > 400 kHz: scllt_fp / sclht_fp
  • otherwise: scllt / sclht
• Add shell command i2c speed <device> <freq_hz>, which calls i2c_configure() with the matching speed.
• Compatibility: 100 kHz and 400 kHz behavior is unchanged. A 1 MHz bus no longer uses scllt/sclht; it uses scllt_fp/sclht_fp, or the computed value if they are not set. All buses that set scllt/sclht in this repo (sb-el, sb-rb) run at 400 kHz, so no existing platform is affected.

Usage

1. DTS (optional, only needed when 1 MHz requires special timing):

   &i2c1a {
       clock-frequency = <I2C_BITRATE_FAST>;
       scllt = <65>;       /* 400 kHz SCL low time */
       sclht = <60>;       /* 400 kHz SCL high time */
       scllt_fp = <xx>;    /* 1 MHz SCL low time, 5 to 255 */
       sclht_fp = <xx>;    /* 1 MHz SCL high time, 5 to 255 */
   };
   

2. Shell:

   uart:~$ i2c speed <device> <freq_hz>
   e.g.
   uart:~$ i2c speed I2C_0 100000
   uart:~$ i2c speed I2C_0 400000
   uart:~$ i2c speed I2C_0 1000000
   

   • freq_hz <= 100000 selects standard mode, <= 400000 fast mode, <= 1000000 fast-plus mode.
   • A value above 1000000 is rejected with "Unsupported speed".

3. Code:

   i2c_configure(dev, I2C_MODE_MASTER | I2C_SPEED_SET(I2C_SPEED_FAST_PLUS));

Test Plan

• Build code: Pass
• Switch bus speed with the shell command and measure SCL with a scope:
  • 100 kHz: <measured frequency>
  • 400 kHz: <measured frequency / SCL low / SCL high>
  • 1 MHz: <measured frequency / SCL low / SCL high>

[meta-codesync]

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