imx8mq 1280x800 HDMI support ( non standard mode )

[adrianb_weissma]

Hi,

We are trying to add support for a 1280x800 10" HDMI display.   We have added entries into the drm_display_mod array named edid_cea_modes found in imx-hdp.c (i.e. Tried adding to edid_cea_modes), as well as table 8 and 9 in t28hpc_hdmitx_table.c.   Our goal is to get a 71.1 Mhz Pixel clock frequency using a VCO of 2844000 KHz.

Our changes were made on the git-imx-4.14.98_2.0.0_ga branch.  We have tried a few other branches with the same luck.  In addition, we are building the imx8mqevk.

After making our changes, we see this in the drm debug output:

[ 1.168077] [drm] Pixel clock frequency: 71100 KHz, character clock frequency: 71100, color depth is 8-bit.
[ 1.168108] [drm] Pixel clock frequency (71100 KHz) is supported in this color depth (8-bit). Settings found in row 8
[ 1.168112] [drm] VCO frequency is 2844000
[ 1.168118] [drm] VCO frequency (2844000 KHz) is supported. Settings found in row 27
[ 1.181820] [drm] CDN_API_General_Write_Register_blocking LANES_CONFIG ret = 0
[ 1.257875] dcss-core 32e00000.dcss: Pixel clock set to 71097 kHz instead of 71100 kHz, difference is -2822 Hz

And the display does not display properly.   We see output, and the boot icon, but there are lines through it.  And it's not really crisp.  After reading through the code, I found an interesting note in dcss-dtg.c   There is a "TODO" note.

The note states "Currently, only modes with pixel clock higher or equal to 74250kHz are working.  Limit to these modes until we figure out how to handle the rest of the display modes."

Well, we were focusing on a 71.1Mhz pixel clock frequency.   However, the note states that this does not work, as its below the 74.250 Mhz frequency.  I am writing to get advice.   Should we try different pixel clock frequencies about 74.250 Mhz?   Say 83.5Mhz for the next possible pixel clock the 1280x800 will support ?   Or is this note no longer valid.

Also, for future plans, what HDMI modes is NXP planning on supporting with the IMX8 family.

Thanks, and your advice would be greatly appreciated.

Cheers,

Adrian

Also, here is a small list of a few of the options we tried:

video=disp.screen0_output_mode=EDID:0      <-- Disable EDID use

mxc_hdmi.only_cea=0                                       <-- Allow non cea modes

video=HDMI-A-1:1280x800-16@60,if=RGB24,bpp=8

[igorpadykov]

Hi Adrian

for such case one can try suggestions provided on

iMX8M HDMI · compulab-yokneam/Documentation Wiki · GitHub 

Best regards
igor
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[adrianb_weissma]

HI Igor,

Thanks, we have seen this webpage.  Thanks for pointing it out.  

The direct question I have is does the IMX8 support the 71.1Mhz clock frequency?   And please elaborate on the comment about not supporting a pixel clock frequency below 74.250 Mhz.

Cheers,

Adrian

[igorpadykov]

Hi Adrian

they way the HDMI is configured is used in our BSP requires specific configuration.

The number of resolution supported comes from the documentation. There is not other

frequencies that can be implemented based on the available documentation.

Best regards
igor
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