1.. SPDX-License-Identifier: GPL-2.0+
2
3How to port an I2C driver to driver model
4=========================================
5
6Over half of the I2C drivers have been converted as at November 2016. These
7ones remain:
8
9   * adi_i2c
10   * davinci_i2c
11   * fti2c010
12   * ihs_i2c
13   * kona_i2c
14   * lpc32xx_i2c
15   * pca9564_i2c
16   * ppc4xx_i2c
17   * rcar_i2c
18   * sh_i2c
19   * soft_i2c
20   * zynq_i2c
21
22The deadline for this work is the end of June 2017. If no one steps
23forward to convert these, at some point there may come a patch to remove them!
24
25Here is a suggested approach for converting your I2C driver over to driver
26model. Please feel free to update this file with your ideas and suggestions.
27
28- #ifdef out all your own I2C driver code (#if !CONFIG_IS_ENABLED(DM_I2C))
29- Define CONFIG_DM_I2C for your board, vendor or architecture
30- If the board does not already use driver model, you need CONFIG_DM also
31- Your board should then build, but will not work fully since there will be
32  no I2C driver
33- Add the U_BOOT_DRIVER piece at the end (e.g. copy tegra_i2c.c for example)
34- Add a private struct for the driver data - avoid using static variables
35- Implement each of the driver methods, perhaps by calling your old methods
36- You may need to adjust the function parameters so that the old and new
37  implementations can share most of the existing code
38- If you convert all existing users of the driver, remove the pre-driver-model
39  code
40
41In terms of patches a conversion series typically has these patches:
42- clean up / prepare the driver for conversion
43- add driver model code
44- convert at least one existing board to use driver model serial
45- (if no boards remain that don't use driver model) remove the old code
46
47This may be a good time to move your board to use device tree also. Mostly
48this involves these steps:
49
50- define CONFIG_OF_CONTROL and CONFIG_OF_SEPARATE
51- add your device tree files to arch/<arch>/dts
52- update the Makefile there
53- Add stdout-path to your /chosen device tree node if it is not already there
54- build and get u-boot-dtb.bin so you can test it
55- Your drivers can now use device tree
56- For device tree in SPL, define CONFIG_SPL_OF_CONTROL
57