question: CSI on imx8mq with (any) CSI2 camera / experience with mx6s_capture?

[Laurent Pinchart]

Hi Martin,

On Tue, Dec 22, 2020 at 03:06:28PM +0100, Martin Kepplinger wrote:
> On 10.12.20 17:04, Laurent Pinchart wrote:
> > On Thu, Dec 10, 2020 at 02:12:30PM +0100, Martin Kepplinger wrote:
> >> On 10.12.20 13:17, Laurent Pinchart wrote:
> >>> On Thu, Dec 10, 2020 at 11:24:00AM +0200, Laurent Pinchart wrote:
> >>>> On Thu, Dec 10, 2020 at 09:17:48AM +0100, Martin Kepplinger wrote:
> >>>>> hi,
> >>>>>
> >>>>> TL;DR: did you use the NXP "mx6s_capture" csi bridge driver with other
> >>>>> cameras?
> >>>>
> >>>> I've recently worked on camera support for i.MX8MM (whose camera IP
> >>>> cores are, if not identical, very similar to the i.MX8MQ's). The least I
> >>>> can say is that it was painful :-(
> >>>>
> >>>> I'm using an MT9M114 sensor, which can produce RAW8, RAW10 and YUV and
> >>>> has a CSI-2 interface. My first use case is to capture RAW10, which
> >>>> isn't supported by the mx6s_capture driver.
> >>
> >> so did you successfully use the NXP mx6s_capture driver with that sensor
> >> too?
> > 
> > I haven't tried. The mx6s_capture driver and the mainline driver share a
> > similar architecture, as they came from the same code base. They have
> > diverged, with the  mainline driver receiving bug fixes and new
> > features, and my large no-yet-upstreamed patch series adds lots of fixes
> > that are required for the mt9m114 driver to work with the driver. For
> > that reason, I've considered that porting the mt9m114 driver to the NXP
> > mx6s_capture, and fixing the same issues in the mx6s_capture driver than
> > were present in the mainline driver, would require lots of time for
> > likely very little gain.
> > 
> > That being said, I've compared the two drivers, and I haven't seen
> > anything in mx6s_capture that would address the specific issues I'm
> > facing. I've ordered yesterday an i.MX8MM EVK with an OV5640 camera
> > module, and I will test those with the mainline driver. If they don't
> > work, and assuming the NXP kernel driver works on that platform, I'll
> > have two code bases to compare.
> > 
> >>>>> I try to use a CSI2 camera (hi846 I'm writing a driver for) on imx8mq:
> >>>>> Using NXP's CSI bridge driver
> >>>>> https://source.codeaurora.org/external/imx/linux-imx/tree/drivers/media/platform/mxc/capture/mx6s_capture.c?h=imx_5.4.0_8dxlphantom_er
> >>>>> as well as the CSI driver itself:
> >>>>> https://source.codeaurora.org/external/imx/linux-imx/tree/drivers/media/platform/imx8/mxc-mipi-csi2_yav.c?h=imx_5.4.0_8dxlphantom_er
> >>>>> works fine when using the ov5640 camera with this driver:
> >>>>> https://source.codeaurora.org/external/imx/linux-imx/tree/drivers/media/platform/mxc/capture/ov5640_mipi_v2.c?h=imx_5.4.0_8dxlphantom_er
> >>>>>
> >>>>> (I realize there is a CSI bridge driver in staging, but that need more
> >>>>> work to be actually used. Of course after this the goal is to fix and
> >>>>> use it; and mainline a CSI phy driver too.)
> >>>>
> >>>> I have lots of patches for this driver, which I've developed on i.MX7D
> >>>> for a separate project. I'd like to mainline them, but this is blocked
> >>>> by one last issue that I haven't been able to solve yet. In a nutshell,
> >>>> the CSI writes two consecutive frames in each buffer, overflowing the
> >>>> allocated memory. The registers that control the buffer size seem to be
> >>>> programmed correctly as far as I can tell. I've reported this issue to
> >>>> NXP but haven't received any feedback yet.
> >>
> >> that's different from where I am. So you don't get any interrupt (EOF or
> >> other) when only *one* frame is written into one buffer?
> > 
> > I don't get any FB1_DMA_DONE or FB2_DMA_DONE interrupt at least. I
> > haven't checked other interrupts. I thus get half of the frame rate. If
> > I configure the CSI_CSIIMAG_PARA register with half of the actual image
> > height, buffers then contain a single image and the frame rate goes to
> > the expected value. That gives me a workaround, but without
> > understanding the root cause, I'm worried that just halving the height
> > would introduce other breakages.
> 
> Hi Laurent,
> 
> Thanks a lot, exchanging things this way alone is much appreciated. I'll 
> give you detailed feedback on the staging drivers later - I tried 
> running them, they probe but still a (gstreamer) stream would not start. 
> But most all of your addition make a lot of sense.
> 
> Just so you know, to emphasize that once more: I'm still on the nxp 
> drivers (yes, they are very similar) just because the ov56 cam works 
> with them over here.

I've recently bought an i.MX8MM EVK, with the OV5647 camera module, and
when I try to capture images, with the NXP kernel, I just don't get any.
*sigh* I'll have to debug that.

> The main problem I have is that, as soon as I try 
> to use a different pixelformat than V4L2_PIX_FMT_YUYV that basically 
> nothing works anymore. userspace stops to "be interested" pretty soon.
> 
> If I do (wrongly) use that pixelformat, I do get (only) one frame (dma) 
> completed, the usual way.
> 
> And when I break the ov56 by using a wrong pixelformat in mx6s_capture 
> (nxp bridge driver), I get equally get only one frame (dma) completed there.
> 
> How can I make this thing use a different pixelformat (by setting the 
> media bus format in the sensor driver)?

All the components have to support the format you want to capture. This
includes the CSI driver, the MIPI_CSI driver, and the OV5647 driver. The
pixel format only matters in the CSI driver, for the other two it's the
media bus format that matters. To capture raw bayer data, you'll first
need to extend the OV5640 driver to support the corresponding media bus
format (and of course configure the sensor to output that format), then
the MIPI_CSI driver to support that media bus format as well, and
finally the CSI driver.

> thanks again for sharing your code early. have a nice rest of the year,

-- 
Regards,

Laurent Pinchart