[PATCH v3 21/24] media: imx: Add MIPI CSI-2 Receiver subdev driver

Russell King - ARM Linux linux at armlinux.org.uk
Tue Jan 31 17:13:49 PST 2017

Hi Steve,

On Tue, Jan 31, 2017 at 05:02:40PM -0800, Steve Longerbeam wrote:
> But this also puts a requirement on MIPI sensors that s_power(ON)
> should only place the D_PHY in LP-11, and _not_ start the clock lane.
> But perhaps that is correct behavior anyway.

If the CSI2 DPHY is held in reset state, it shouldn't matter what the
sensor does.  In the case of IMX219, it needs a full setup of the
device, including enabling it to stream (so it starts the clock lane
etc) in order to get it into LP-11 state.  Merely disabling the XCLR
signal leaves the lanes grounded.

I do seem to remember reading in one of the MIPI specs that this is
rather expected behaviour, though I can't point at a paragraph this
late in the night.

So, the only way to satisfy these requirements is this order:

- assert PHY reset signals (so blocking any activity on the CSI lanes)
- initialise the sensor (including allowing it to start streaming and
  then stopping the stream - at that point, the lanes will be in LP-11.)
- deassert the resets as per the iMX6 documentation and follow the
  remaining procedure.

I'll look at your other points tomorrow.


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