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

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Petko,

On Thu, Jul 07, 2022 at 03:17:51PM +0300, Petko Manolov wrote:
> 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".

And I think it's also wrong in the imx7-media-csi driver. I've sent a
pull request ([1]) for v5.20 that should fix this, in particular in
patch "staging: media: imx: imx7-media-csi: Fix list of supported
formats" ([2]).

[1] https://lore.kernel.org/linux-media/YsbEoobPgKoYcZUs@pendragon.ideasonboard.com/
[2] https://lore.kernel.org/linux-media/20220510115859.19777-46-laurent.pinchart@ideasonboard.com/

> > 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.

Thank you. The pull request has been sent, so this should be fixed in
v5.20.

> 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?

There's no real rule about the maximum amount of memory V4L2 driver
can/should allocate. Every driver sets its own limits (and some drivers
don't set a limit at all). 64MB is clearly too little. Feel free to
submit a patch to increase this in the imx7-media-csi driver (on top of
[1] to avoid conflicts).

-- 
Regards,

Laurent Pinchart