Re: Re: Re: hooking Sony 47MPixel sensor to NXP imx8m-mini MIPI CSI2

[Petko Manolov <petko.manolov@konsulko.com>]

On 22-07-07 00:47:21, Laurent Pinchart wrote:
> 
> MEDIA_BUS_FMT_* are media bus formats, they describe the format of data as it
> gets transmitted on buses between entities. The main purposes of those formats
> are configuration of entities in the pipeline (an IP core will need to be
> configured differently if it receives 10-bit raw data or 12-bit raw data for
> instance), and validation of the pipeline configuration (the format on the
> output of an entity must match the format on the input of the next entity).
> 
> V4L2_PIX_FMT_* are pixel formats, and they describe the format of data as
> stored in memory. They're only meaningful for the DMA engines at the end of
> the pipeline, and while they're related to the media bus formats (the DMA
> engine can't write to memory, for instance, V4L2_PIX_FMT_YUYV if it receives
> MEDIA_BUS_FMT_SGRBG10 from the previous entity), there's no fixed 1:1 mapping
> between the two formats. The mapping is device-dependent. For instance, a DMA
> engine that receives YUV 4:2:2 data in the form of MEDIA_BUS_FMT_YUYV8_1X16
> could support writing it in different pixel formats, such as
> V4L2_PIX_FMT_YUYV, V4L2_PIX_FMT_NV12, V4L2_PIX_FMT_NV16, ...

Thanks for these details.

I was wondering why V4L2_PIX_FMT_SGBRG12 would not be used for
MEDIA_BUS_FMT_SGBRG12_1X12 bus formats, but i guess the answer i can extract
from the info above is "device dependent".

> I have work in progress patches that address issues with the imx7-csi-bridge
> driver, once they land we could look into this. I'm afraid I'm a bit slow
> these days due to covid.

Quick recovery!  Looking forward to these patches.

For me, changing VID_MEM_LIMIT to 512MB works OK for the moment.  I am not yet
certain how this constant is related to the global CMA parameter.  In the
default kernel config CMA is 32MB, while VID_MEM_LIMIT is 64MB.  Isn't this
wrong?


		Petko