Re: [PATCH 1/2] media: dt-bindings: media: xilinx: Add Xilinx MIPI CSI-2 Rx Subsystem

[Sakari Ailus <sakari.ailus@linux.intel.com>]

Hi Vishal,

On Mon, Jan 14, 2019 at 09:47:41AM +0000, Vishal Sagar wrote:
> Hi Sakari,
> 
> Thanks for reviewing this. 
> 
> > -----Original Message-----
> > From: Sakari Ailus [mailto:sakari.ailus@linux.intel.com]
> > Sent: Tuesday, January 08, 2019 6:35 PM
> > To: Vishal Sagar <vishal.sagar@xilinx.com>
> > Cc: Hyun Kwon <hyunk@xilinx.com>; laurent.pinchart@ideasonboard.com;
> > Michal Simek <michals@xilinx.com>; linux-media@vger.kernel.org;
> > devicetree@vger.kernel.org; hans.verkuil@cisco.com; mchehab@kernel.org;
> > robh+dt@kernel.org; mark.rutland@arm.com; Dinesh Kumar
> > <dineshk@xilinx.com>; linux-arm-kernel@lists.infradead.org; linux-
> > kernel@vger.kernel.org
> > Subject: Re: [PATCH 1/2] media: dt-bindings: media: xilinx: Add Xilinx MIPI CSI-2
> > Rx Subsystem
> > 
> > EXTERNAL EMAIL
> > 
> > Hi Vishal,
> > 
> > The patchset hard escaped me somehow earlier and your reply to Rob made me
> > notice it again. Thanks. :-)
> > 
> > On Wed, May 30, 2018 at 12:24:43AM +0530, Vishal Sagar wrote:
> > > Add bindings documentation for Xilinx MIPI CSI-2 Rx Subsystem.
> > >
> > > The Xilinx MIPI CSI-2 Rx Subsystem consists of a DPHY, CSI-2 Rx, an
> > > optional I2C controller and an optional Video Format Bridge (VFB). The
> > > active lanes can be configured at run time if enabled in the IP. The
> > > DPHY register interface may also be enabled.
> > >
> > > Signed-off-by: Vishal Sagar <vishal.sagar@xilinx.com>
> > > ---
> > >  .../bindings/media/xilinx/xlnx,csi2rxss.txt        | 117
> > +++++++++++++++++++++
> > >  1 file changed, 117 insertions(+)
> > >  create mode 100644
> > Documentation/devicetree/bindings/media/xilinx/xlnx,csi2rxss.txt
> > >
> > > diff --git a/Documentation/devicetree/bindings/media/xilinx/xlnx,csi2rxss.txt
> > b/Documentation/devicetree/bindings/media/xilinx/xlnx,csi2rxss.txt
> > > new file mode 100644
> > > index 0000000..31ed721
> > > --- /dev/null
> > > +++ b/Documentation/devicetree/bindings/media/xilinx/xlnx,csi2rxss.txt
> > > @@ -0,0 +1,117 @@
> > > +
> > 
> > Extra newline.
> > 
> 
> Will remove it in next version. 
> 
> > > +Xilinx MIPI CSI2 Receiver Subsystem Device Tree Bindings
> > > +--------------------------------------------------------
> > > +
> > > +The Xilinx MIPI CSI2 Receiver Subsystem is used to capture MIPI CSI2 traffic
> > > +from compliant camera sensors and send the output as AXI4 Stream video
> > data
> > > +for image processing.
> > > +
> > > +The subsystem consists of a MIPI DPHY in slave mode which captures the
> > > +data packets. This is passed along the MIPI CSI2 Rx IP which extracts the
> > > +packet data. This data is taken in by the Video Format Bridge (VFB),
> > > +if selected, and converted into AXI4 Stream video data at selected
> > > +pixels per clock as per AXI4-Stream Video IP and System Design UG934.
> > > +
> > > +For more details, please refer to PG232 MIPI CSI-2 Receiver Subsystem.
> > >
> > +https://www.xilinx.com/support/documentation/ip_documentation/mipi_csi
> > 2_rx_subsystem/v3_0/pg232-mipi-csi2-rx.pdf
> > > +
> > > +Required properties:
> > > +
> > > +- compatible: Must contain "xlnx,mipi-csi2-rx-subsystem-2.0" or
> > > +  "xlnx,mipi-csi2-rx-subsystem-3.0"
> > > +
> > > +- reg: Physical base address and length of the registers set for the device.
> > > +
> > > +- interrupt-parent: specifies the phandle to the parent interrupt controller
> > > +
> > > +- interrupts: Property with a value describing the interrupt number.
> > > +
> > > +- xlnx,max-lanes: Maximum active lanes in the design.
> > > +
> > > +- xlnx,vc: Virtual Channel, specifies virtual channel number to be filtered.
> > > +  If this is 4 then all virtual channels are allowed.
> > 
> > This seems like something a driver should configure, based on the
> > configuration of the connected device.
> > 
> 
> The filtering of the Virtual channels is property of the hardware IP and is fixed in design. 
> This is not software controlled.

So... you have different IP blocks between which (one of) the difference(s)
is the virtual channel?

> 
> > > +
> > > +- xlnx,csi-pxl-format: This denotes the CSI Data type selected in hw design.
> > > +  Packets other than this data type (except for RAW8 and User defined data
> > > +  types) will be filtered out. Possible values are RAW6, RAW7, RAW8, RAW10,
> > > +  RAW12, RAW14, RGB444, RGB555, RGB565, RGB666, RGB888 and
> > YUV4228bit.
> > 
> > This should be configured at runtime instead through V4L2 sub-device
> > interface; it's not a property of the hardware.
> >
> 
> This too is a property of the hardware IP and is fixed to one data type
> during design to reduce gate count. So for e.g. if RGB888 is selected
> during design, then the hardware will only pass across RGB888 packet data
> to output. (RAW8 packets are also allowed to pass through for all data
> types selected) This is used in the driver to determine the media bus
> format of the connected pads.

If I understand this correctly, RAW8 and user defined data types will
always pass through, plus the other data types listed here. Is that right?

> 
> > > +
> > > +- xlnx,axis-tdata-width: AXI Stream width, This denotes the AXI Stream width.
> > > +  It depends on Data type chosen, Video Format Bridge enabled/disabled and
> > > +  pixels per clock. If VFB is disabled then its value is either 0x20 (32 bit)
> > > +  or 0x40(64 bit) width.
> > > +
> > > +- xlnx,video-format, xlnx,video-width: Video format and width, as defined in
> > > +  video.txt.
> > 
> > Ditto.
> > 
> Again these are fixed values and can't be changed at run time. 
> These are used to determine the media bus format.

What kind of values can the xlnx,video-format property have? How about
xlnx.video-width? Where can video.txt be found?

> 
> > > +
> > > +- port: Video port, using the DT bindings defined in ../video-interfaces.txt.
> > > +  The CSI 2 Rx Subsystem has a two ports, one input port for connecting to
> > > +  camera sensor and other is output port.
> > > +
> > > +- data-lanes: The number of data lanes through which CSI2 Rx Subsystem is
> > > +  connected to the camera sensor as per video-interfaces.txt
> > 
> > This is somewhat different from the documentation in video-interfaces.txt.
> > Could you align the two? I don't think there's a need to document standard
> > properties in device binding files elaborately; rather just the hardware
> > specific bits.
> > 
> 
> Agree. In this current IP there is no way to re-order the lanes which are set at design time.
> So physical and logical lanes are at same index. This could only be used to determine how many lanes are allowed to be programmed.
> For e.g. if design has set the number of lanes as 4 and xlnx,en-active-lanes is present, then the number of lanes 
> can be set from 1 to 4.

Ack.

-- 
Regards,

Sakari Ailus
sakari.ailus@linux.intel.com