U5 and display issues

[pll]

We are using the STM32U5A9J-DK with another display from an older development kit (STM32L4R9-DISCO). The display 390x390 is driven with the MIPI-DSI interface in adapted command mode.

After a first full screen refresh, we are refreshing only portions of the screen (5 rectangles with different background colors). The rectangle in the middle is refreshed just after the background.

As you can see on the picture, the inside is wrongly refreshed (double vertical line on the left). If we add a delay (1.5 ms) between changing the LTDC layer registers and the LTDC immediate register reload (LTDC_SRCR.IMR = 1), then the system was working as expected.

We are wondering why we need to add this delay. It is annoying us, because of performance reasons.

Got somebody the same experience? Any advice is welcome?    

buggy resultexpected result

[Mohammad MORADI ESFAHANIASL]

Hello @pll ,

The delay might help due to synchronization reasons. It is pretty hard to say from here what is causing the issue, but I suggest checking out the implementation for the STM32F769I-Discovery kit Board Setup available in the TouchGFX designer since it uses MIPI-DSI display, although, it is in command mode. 
Maybe, try setting the scanline to 0 or 390 and observe how the behavior changes. 

If you couldn't find any clues, please share your project so, we can also examine it.  .

Good luck,