i.MX8MQ: clarification on MIPI RGB888

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i.MX8MQ: clarification on MIPI RGB888

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gianfranco
Contributor II

Dear Support Team,

I'm working on a custom iMX8MQ board with an image sensor sending RBG888 data over MIPI lanes. After reading the iMX8 reference manual and the NXP Community forum I have some doubts on MIPI-CSI Host Controller and CSI-bridge drivers concerning the RGB888 support. Below you can find a list of questions:

I modified the mx6_capture.c driver to support the RGB888:

CSI_CR18 register: MIPI_DATA_FORMAT bits set to 0x24 (RGB8888), RGB888A_FORMAT_SELECTION bit set to 0 (I want the padding byte at most significant part of image data), PARALLEL24_EN bit set to 1. 

CSI_CR3 register: SENSOR_16BITS set to 0

Added a new internal CSI-bridge format as follows (I used BGR because my camera is sending data in this order, user space app will interpret them accordingly):

        .name = "BGR24",
        .fourcc = V4L2_PIX_FMT_BGR24,
        .pixelformat = V4L2_PIX_FMT_BGR24,
        .mbus_code = MEDIA_BUS_FMT_BGR888_1X24,
        .bpp = 4
 
The first question is: Is it correct to have 4 as byte per pixels (bpp field) ? I read that the iMX8M CSI-Bridge cannot disable the zero byte padding when working in RGB888 mode. For these reason I used 4 bytes per pixel instead of 3. 
 
I modified the MIPI HOST controller driver (mxc_mipi_csi.c) to support the RGB888 as well:
 
I added a new internal format:
 
 { /* Used for RGB888 */
        .code = MEDIA_BUS_FMT_BGR888_1X24,
        .fmt_reg = MIPI_CSIS_ISPCFG_FMT_RGB888,
        .data_alignment = 24, 
 }
 
The question here is: is it right to have 24 as data alignment? 
In my custom board I just use the MIPI HOST CONTROLLER CAM I/F and not the ISP I/F (I'm not sure there is an ISP peripheral on iMX8M board actually) so the fmt_reg and data_alignment settings should be irrelevant in this case. Is it right? 
 
Thanks for your help,
Gianfranco
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AldoG
NXP TechSupport
NXP TechSupport

Hello,

Your changes look correct, are you facing any issues with the changes you have made?
Also, regarding ISP you are correct i.MX8MQ does not have ISP so it should be fine.

Best regards,
Aldo.

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gianfranco
Contributor II

Hello,

thanks for your reply. I'm not experiencing any particular issue so far. I just wanted to double check the correct configuration.

Thanks

Gianfranco

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