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

[Laurent Pinchart]

Hi Martin,

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.

> >> I've also added support for i.MX8MM to this driver, but haven't been
> >> able to capture RAW8, RAW10 or YUV successfully. YUV produces the "best
> >> images", but seems to drop 3 out of 4 consecutive pixels. The sensor
> >> driver has been tested successfully on i.MX6 so I don't think it's the
> >> most likely cause of issues, but I can't rule out bugs on that side
> >> either. The i.MX8 reference manuals describe the MIPI_CSI and CSI IP
> >> cores but doesn't tell much about how the two are connected, so I have
> >> lots of unanswered questions about the register fields that control the
> >> interface between those IP cores. I'm pretty sure there are issues in
> >> that area of the drivers, but I've tested all combinations I could think
> >> of, without luck.
> >>
> >>> Now I use said NXP's CSI drivers on mainline without problems with the
> >>> ov5640. For the hi846 (as an example), I want to use a different
> >>> pixelformat and CSI media bus format. Describing, say,
> >>> MEDIA_BUS_FMT_SBGGR10_1X10 in the driver lets mx6s_capture find it; but
> >>> as soon as I try to add a different pixelformat than V4L2_PIX_FMT_UYVY in:
> >>> https://source.codeaurora.org/external/imx/linux-imx/tree/drivers/media/platform/mxc/capture/mx6s_capture.c?h=imx_5.4.0_8dxlphantom_er#n244
> >>> streaming won't start anymore: "not negotiated, -4" and the
> >>> "mx6s_vidioc_enum_framesizes" ioctl is not called anymore. Why so?
> >>
> >> That will likely be the easy part of the problem. The NXP driver doesn't
> >> support RAW10 at all, so you will have to add that, and I don't think it
> >> will be easy.
> 
> the staging driver (imx7-media-csi) sets PIXEL_BIT (cr1) and 
> BIT_MIPI_DATA_FORMAT_RAW10 (cr18) which I hoped to be enough for 
> supporting RAW10. What else do you think is missing?

That I don't know, given that I haven't been able to get RAW10 to work
correctly with the staging driver yet :-)

> >> I'll push my development branch shortly if you're interested in trying
> >> the mainline driver.
> > 
> > 	git://linuxtv.org/pinchartl/media.git imx/csi/imx8
> > 
> > The topmost patches are random debugging tests.
> 
> Thanks a lot. I'll definitely have a look and try running imx7-media-csi 
> once more.
> 
> >>> I didn't find much when comparing strace from "gst-launch-1.0 v4l2src !
> >>> video/x-raw,width=1280,height=720 ! videoconvert ! xvimagesink" (which
> >>> is how I test).
> >>>
> >>> When I simply use V4L2_PIX_FMT_UYVY I *do* get interrupts (in mx6s) but
> >>> only "FIELD0_INT" (and drawing at this point suggests that buffer 1 is
> >>> not yet full and "distorted" in a wrong format, which could explain why
> >>> DMA is never completed in order to create a full frame).
> >>>
> >>> Now this is details, but the hi846 camera uses a 10bit CSI format and
> >>> therefore I need to set PIXEL_BIT in cr1 too, but when I do that for
> >>> example, I don't get "FIELD0_INT" anymore (only SFF_OR_INT and of course
> >>> the "base address switching Change Err").
> >>>
> >>> Do you have experience with using this driver with other cameras and can
> >>> point me in a direction that might help me?
> >>>
> >>> If you want to look at the work-in-progress driver:
> >>> https://source.puri.sm/martin.kepplinger/linux-next/-/blob/hi846/drivers/media/i2c/hi846.c

-- 
Regards,

Laurent Pinchart