Am Mittwoch, den 19.10.2016, 15:59 +0300 schrieb Sakari Ailus: > Document the interface between the CSI-2 transmitter and receiver drivers. > > Signed-off-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx> > --- > Hi Philipp, > > Indeed the pixel rate is used by some driver as well. > > How about this one instead? > > The HTML page is available here (without CCS unfortunately): > > <URL:http://www.retiisi.org.uk/v4l2/tmp/csi2.html> > > since v1: > > - Add PIXEL_RATE to the required controls. > > - Document how pixel rate is calculated from the link frequency. > > Documentation/media/kapi/csi2.rst | 59 ++++++++++++++++++++++++++++++++++++++ > Documentation/media/media_kapi.rst | 1 + > 2 files changed, 60 insertions(+) > create mode 100644 Documentation/media/kapi/csi2.rst > > diff --git a/Documentation/media/kapi/csi2.rst b/Documentation/media/kapi/csi2.rst > new file mode 100644 > index 0000000..31f927d > --- /dev/null > +++ b/Documentation/media/kapi/csi2.rst > @@ -0,0 +1,59 @@ > +MIPI CSI-2 > +========== > + > +CSI-2 is a data bus intended for transferring images from cameras to > +the host SoC. It is defined by the `MIPI alliance`_. > + > +.. _`MIPI alliance`: http://www.mipi.org/ > + > +Transmitter drivers > +------------------- > + > +CSI-2 transmitter, such as a sensor or a TV tuner, drivers need to > +provide the CSI-2 receiver with information on the CSI-2 bus > +configuration. These include the V4L2_CID_LINK_FREQ and > +V4L2_CID_PIXEL_RATE controls and > +(:c:type:`v4l2_subdev_video_ops`->s_stream() callback). These > +interface elements must be present on the sub-device represents the > +CSI-2 transmitter. > + > +The V4L2_CID_LINK_FREQ control is used to tell the receiver driver the > +frequency (and not the symbol rate) of the link. The > +V4L2_CID_PIXEL_RATE is may be used by the receiver to obtain the pixel > +rate the transmitter uses. The > +:c:type:`v4l2_subdev_video_ops`->s_stream() callback provides an > +ability to start and stop the stream. > + > +The value of the V4L2_CID_PIXEL_RATE is calculated as follows:: > + > + pixel_rate = link_freq * 2 * nr_of_lanes This is the total bps, which must be divided by the bits per pixel depending on the selected MEDIA_BUS_FMT, for example /16 for MEDIA_BUS_FMT_UYVY8_1X16, or /24 for MEDIA_BUS_FMT_RGB888_1X24, to obtain pixel_rate. > +where > + > +.. list-table:: variables in pixel rate calculation > + :header-rows: 1 > + > + * - variable or constant > + - description > + * - link_freq > + - The value of the V4L2_CID_LINK_FREQ integer64 menu item. > + * - nr_of_lanes > + - Number of data lanes used on the CSI-2 link. This can > + be obtained from the OF endpoint configuration. I suppose the number of lanes should be calculated as nr_of_lanes = DIV_ROUND_UP(pixel_rate * bpp, link_freq * 2) in the receiver driver? Not all lanes configured in the device tree have to be used, depending on the configured link frequencies and bus format. > + * - 2 > + - Two bits are transferred per clock cycle per lane. > + > +The transmitter drivers must configure the CSI-2 transmitter to *LP-11 > +mode* whenever the transmitter is powered on but not active. Some > +transmitters do this automatically but some have to be explicitly > +programmed to do so. > + > +Receiver drivers > +---------------- > + > +Before the receiver driver may enable the CSI-2 transmitter by using > +the :c:type:`v4l2_subdev_video_ops`->s_stream(), it must have powered > +the transmitter up by using the > +:c:type:`v4l2_subdev_core_ops`->s_power() callback. This may take > +place either indirectly by using :c:func:`v4l2_pipeline_pm_use` or > +directly. > diff --git a/Documentation/media/media_kapi.rst b/Documentation/media/media_kapi.rst > index f282ca2..bc06389 100644 > --- a/Documentation/media/media_kapi.rst > +++ b/Documentation/media/media_kapi.rst > @@ -33,3 +33,4 @@ For more details see the file COPYING in the source distribution of Linux. > kapi/rc-core > kapi/mc-core > kapi/cec-core > + kapi/csi2 regards Philipp -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
