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

[Laurent Pinchart]

Hi Martin,

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.
> 
> > 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.
> 
> 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.
> 
> 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.

> > 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