What is worse than no comments? Wrong comments!
The panel-simple driver requires an enable-gpio. But since the used panel has no enable input this pin isn’t used on our carrier board and the pin definition is meaningless. I’m using the same panel-node definition in the device tree for the imx8mm without any problems.
Yes. Since the imx8mm and imx8mp have the same kernel source I’m using the same patch for the panel-simple driver to add the timings and characteristics of our panel.
When I disable the patch the error remains the very same. So I would assume the error happens before the panel-simple driver is even called.
the longer you search for a bug, the smaller the fix is.
The reason for error -19 was a line in the overlay in which I changed the PWM polarity of the backlight. Node pwm1 was used instead of node pwm3. I unfortunately omitted this line in my start post.
But even after correcting this error, the display remained dark. The cause was that the MIPI_DSI_MODE_LPM flag was set in my driver patch for the display.
The GPU driver for the iMX8MM seems to ignore this flag, whereas it is relevant for the iMX8MP.
And as soon as you do it right, it works …
During my tests, however, I noticed that the kernel 5.15.129 of BSP V6.4 shows a different behavior. With version 5.15.77 of V6.3, the display is loaded correctly immediately, but with V6.4 it only works on the second attempt. The first time there is again an error -19 (failed to attach bridge).
To reproduce this behavior, it is sufficient to create a tdx-reference-minimal-image and write this overlay into the overlay.txt: verdin-imx8mp_panel_simple_vvx10f004b00.dts (1.2 KB)
In addition, the tv080wum-nl0 panel from the panel-simple.c driver works with BSP6.3, while error -22 (unsupported dsi mode) occurs with BSP 6.4. With the panel ld070wx3-sl01 it is the other way around.