i2c_samd0.c burst write not compatible with ssd1306.c

[Tubbles]

Running Zephyr with a SSD1306 compatible OLED screen does not work over I2C

I am running with a seeeduino xiao and its accompanying dev kit which features a SSD1306 compatible 128x64 pixels OLED screen, accessed over the I2C bus.

Comparing with a similar library from the Arduino ecosystem I saw that the I2C packets of Zephyr was incorrectly chopped up into smaller chunks. I tracked it down and it seems that it comes from the usage of i2c_burst_write(), but I don't know what is the supposed behavior of the I2C driver. Is it okay for it to inject STOP conditions between each I2C message? There is a warning in the header file which seems to indicate that it is.

To Reproduce

1. checkout the below zephyr version
2. apply the changes in the below attached patch (except the one for the ssd1306.c file which contains a workaround)
3. unpack blinken.zip below
4. west build -b seeeduino_xiao
5. west flash
6. See error

Expected behavior
A stripey pattern on the display

Impact
Showstopper for any application using this driver combo (and possibly others with the ssd1306?)

Logs and console output
Expected comms:

Actual comms:

Environment (please complete the following information):

• Manjaro Linux
• zephyr-v2.6.0-740-gc32a96af6ade

Additional context
0001-seeduino-xiao-add-i2c-support-fix-ssd1306-burst-writ.patch.txt
blinken.zip

[jfischer-no]

This is not a ssd1306 controller driver issue but i2c_samd0.c driver bug/incompatibility.

[Tubbles]

This is not a ssd1306 controller driver issue but i2c_samd0.c driver bug/incompatibility.

Is there some more specification anywhere on how the API implementer is supposed to handle this situation? If it is a bug, we need to fix the driver; on the other hand, if its an incompatibility, we need to change what API we are using..

[carlescufi]

@Tubbles there is a lengthy discussion regarding i2c burst writes in this PR. If your issue is similar to this maybe you want to weigh in there.

[rustypig91]

This is not a ssd1306 controller driver issue but i2c_samd0.c driver bug/incompatibility.

Stumbled across the same issue with ssd1306 and seeeduino xiao
This is my fix rustypig91@ee7d890

[dstahlke]

@rustypig91 This fix works for me, for both the Adafruit OLED FeatherWing (SH1107) and the common 0.96" OLED breakout board (SSD1306?). Very nice work - it took way too much time to debug this to the point where I found this ticket. Could you submit a pull request for this?

[dstahlke]

i2c_burst_write does have a warning saying it's not portable and doesn't work correctly on some devices. It'd be nice if ssd1306.c could use i2c_transfer instead.

Looking through the code, it appears this would be easy to do for all the command buffers (just prepend the command byte), but for ssd1306_write would not be so easy because the data comes from a user-supplied buffer.