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Hi all,

We are working on an i.MX8MM  evk board. We are currently using the example Embedded wizard project (for libdrm and opgengl). We use the imx specific kernel tree (version 6.1.y).

When we boot the device, the Linux boot logo is nicely displayed, and we can write to the framebufer device directly (/dev/fb0 in our case). Then, when we launch the embedded wizard application, the content that we write to the framebuffer device is no longer being displayed. The embedded wizard GUI is shown instead. So far, the board always behaves the same way.

 

When we close the application, the behavior starts to differ. In roughly half of the  cases, the screen turns black and then after a second displays the content of the framebuffer device again. In the other case, the screen also becomes black, but remains black indefinitely. When the framebuffer device is displayed, the screen shows the embedded wizard GUI again when the application is restarted. When the screen remains black, the GUI is not shown when we restart the application.

Using strace, I can see that even when the content is not shown, the application is running. We also cannot see any differences in the called syscalls for the two cases.

 

Has anyone seen similar behavior? Is this expected behavior?

 

Kind regards,

Yoshi Vermeire

1 Answer

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Hi Yoshi,
I never tried to write directly to the framebuffer device on a i.MX8MM environment and how it behaves in combination with a libdrm based application.
However, I could imagine, that a reason for the described behaviour could be, that the Embedded Wizard application changes the graphical mode (drmModeSetCrtc()) but it doesn't restore it to the previous mode on termination.
Maybe for output via a framebuffer device another mode is needed. You could retrieve the previous setting using drmModeGetCrtc() before the mode is changed in gfx_system_drm.c. However, please note, that this is just an assumption.
Did you ever tried with another libdrm based application?

Regards,
Martin

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