Hi Philipp, Thanks a lot for your response.
On Fri, Apr 13, 2018 at 4:18 PM, Philipp Zabel <p.za...@pengutronix.de> wrote: > Hi Ibtsam, > > On Thu, 2018-04-12 at 16:00 +0200, Ibtsam Ul-Haq wrote: >> Greetings everyone, >> I am using Linux 4.14.31 on an IMX6 platform, with an MT9P031 sensor >> attached to the ipu1_csi0 (parallel). >> My Gstreamer version is 1.14.0 and v4l-utils version is 1.14.2. >> The problem is that I am unable to set up a capture pipeline. >> >> Even the simplest capture pipeline such as: >> >> gst-launch-1.0 v4l2src device=/dev/video4 ! fakesink >> >> returns the following error: >> ERROR: from element /GstPipeline:pipeline0/GstV4l2Src:v4l2src0: >> Internal data stream error. >> Additional debug info: >> ../../../../gstreamer-1.14.0/libs/gst/base/gstbasesrc.c(3055): >> gst_base_src_loop (): /GstPipeline:pipeline0/GstV4l2Src:v4l2src0: >> streaming stopped, reason not-negotiated (-4) >> ERROR: pipeline doesn't want to preroll. >> >> I get the same error on any pipeline involving v4l2src. >> >> I have set up the media entity links using: >> media-ctl -l "'mt9p031 0-0048':0 -> 'ipu1_csi0_mux':1" >> media-ctl -l "'ipu1_csi0_mux':2 -> 'ipu1_csi0':0" >> media-ctl -l "'ipu1_csi0':2 -> 'ipu1_csi0 capture':0" >> >> And I configure the pads using: >> media-ctl -V "'mt9p031 0-0048':0 [fmt:SGRBG8/640x480 field:none]" >> media-ctl -V "'ipu1_csi0_mux':2 [fmt:SGRBG8/640x480 field:none]" >> media-ctl -V "'ipu1_csi0':2 [fmt:SGRBG8/640x480 field:none]" > > What is the actual format that all pads are configured to? I found it > helpful to double check the whole pipeline after configuring pads (or > use media-ctl -v): > > media-ctl --get-v4l2 "'mt9p031 0-0048':0" > media-ctl --get-v4l2 "'ipu1_csi0_mux':1" > media-ctl --get-v4l2 "'ipu1_csi0_mux':2" > media-ctl --get-v4l2 "'ipu1_csi0':0" > media-ctl --get-v4l2 "'ipu1_csi0':2" > Here is what I get after I have executed the commands to configure all the pads to SGRBG8/640x480: :~# media-ctl --get-v4l2 "'mt9p031 0-0048':0" [fmt:SGRBG12_1X12/648x486 field:none colorspace:srgb :~# media-ctl --get-v4l2 "'ipu1_csi0_mux':1" [fmt:SGRBG12_1X12/648x486 field:none colorspace:srgb] :~# media-ctl --get-v4l2 "'ipu1_csi0_mux':2" [fmt:SGRBG12_1X12/648x486 field:none colorspace:srgb] :~# media-ctl --get-v4l2 "'ipu1_csi0':0" [fmt:SGRBG12_1X12/656x486@1/30 field:none colorspace:srgb xfer:srgb ycbcr:601 quantization:full-range crop.bounds:(0,0)/656x486 crop:(0,0)/656x486 compose.bounds:(0,0)/656x486 compose:(0,0)/656x486] :~# media-ctl --get-v4l2 "'ipu1_csi0':2" [fmt:SGRBG12_1X12/656x486@1/30 field:none colorspace:srgb xfer:srgb ycbcr:601 quantization:full-range] > I assume that because mt9p031 only supports SGRBG12_1X12, that's what > will be propagated down the pipeline to the CSI, which will then expand > it to SGRBG16. > This indeed looks the case. But then, is 'GR16' the FourCC for 'SGRBG16'? To be honest, I had not seen GR16 as FourCC before. And the Gstreamer debug logs (I used GST_DEBUG=5) also say that they do not know this FourCC: v4l2 gstv4l2object.c:1541:gst_v4l2_object_v4l2fourcc_to_bare_struct: [00m Unsupported fourcc 0x36315247 GR16 Is there a way we can get by this? > I suppose we should allow, at least for parallel input, to let the CSI > 'convert' 12-bit input formats to 8-bit output formats by just ignoring > the LSBs. > Another possibility would be to just allow SGRBG12_1X12 -> SGRBG8_1X8 > mbus codes in link_validate. Actually, does your hardware have 12 data > lines connected between sensor and i.MX6, or just 8 ? > Currently we have 8. Although we can populate extra resistors to connect the remaining 4. The device tree is set for 8 lines currently. >> And I do not get any errors from these commands. > > That's because of the way the V4L2 API works, unsupported formats are > adjusted by the drivers: > > https://linuxtv.org/downloads/v4l-dvb-apis-new/uapi/v4l/vidioc-subdev-g-fmt.html#description > > [...] >> What confuses me here is that the Pixel Format shown by v4l2-ctl is >> 'GR16', which is not what I expected. And it seems like the media-ctl >> pad configuration commands are unable to change the Pixel Format, even >> though they do not return any errors. > > Whenever you media-ctl -V on a source pad, it will also try to set the > connected sink pad to the same format. And for subdevices with sink and > source pads, the source pads usually mirror (or somehow depend on) the > format of the sink pad. Due to the way the V4L2 APIs correct your input > to possible values, calling media-ctl -V on all source pads of the > pipeline in downstream direction essentially propagates the sensor > source pad format. > Thanks for the nice explanation. This is valuable learning for me as I am just a beginner in this stuff. > regards > Philipp Best regards, Ibtsam Haq